PCI 6th EditionPCI 6th Edition

Fabrication Design

Presentation OutlinePresentation Outline

bull Planning Discussionbull Stripping Process Design and Analysisbull Prestress Post Tension Effectsbull Handling Devicesbull Stripping Stress Examplesbull Storage Discussionbull Transportation Discussionbull Erection Discussion

IntroductionIntroduction

bull The loads and forces on precast and prestressed concrete members during production transportation or erection will frequently require a separate analysis

bull Concrete strengths are lowerbull Support points and orientation are usually

different from members in their final position

Pre-Planning Piece SizePre-Planning Piece Size

The most economical piece size for a project is usually the largest considering the following factors

bull Stability and stresses on the element during handling

bull Transportation size and weight regulations and equipment restrictions

Pre-Planning Piece SizePre-Planning Piece Size

bull Available crane capacity at both the plant and the project site

bull Position of the crane must be considered since capacity is a function of reach

bull Storage space truck turning radius and other site restrictions

Planning and SetupPlanning and Setup

bull Once a piece has been fabricated it is necessary to remove it from the mold without being damaged

bull Positive drafts or breakaway forms should be used to allow a member to lift away from the casting bed without becoming wedged within the form

bull Adequate draft also serves to reduce trapped air bubbles

Planning and SetupPlanning and Setup

bull Lifting points must be located to keep member stresses within limits and to ensure proper alignment of the piece as it is being lifted

bull Members with unsymmetrical geometry or projecting sections may require supplemental lifting points and auxiliary lifting lines to achieve even support during handling

bull ldquoCome-alongsrdquo or ldquochain-fallsrdquo are frequently used for these auxiliary lines

Planning and SetupPlanning and Setup

bull When the member has areas of small cross section or large cantilevers it may be necessary to add a structural steel ldquostrongbackrdquo to the piece to provide added strength

Planning and SetupPlanning and Setup

bull Members that require a secondary process prior to shipment such as sandblasting or attachment of haunches may need to be rotated at the production facility In these cases it may be necessary to cast in extra lifting devices to facilitate these maneuvers

Planning and SetupPlanning and Setup

bull When developing member shapes the designer should consider the extra costs associated with special rigging or forming and pieces requiring multiple handling

Stripping GeneralStripping General

bull Orientation of members during storage shipping and final in-place position is critical in determining stripping requirements

bull They can be horizontal vertical or some angle in betweenbull The number and location of lifting devices are chosen to keep stresses within

the allowable limits which depends on whether the ldquono crackingrdquo or ldquocontrolled crackingrdquo criteria is to be used

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Presentation OutlinePresentation Outline

bull Planning Discussionbull Stripping Process Design and Analysisbull Prestress Post Tension Effectsbull Handling Devicesbull Stripping Stress Examplesbull Storage Discussionbull Transportation Discussionbull Erection Discussion

IntroductionIntroduction

bull The loads and forces on precast and prestressed concrete members during production transportation or erection will frequently require a separate analysis

bull Concrete strengths are lowerbull Support points and orientation are usually

different from members in their final position

Pre-Planning Piece SizePre-Planning Piece Size

The most economical piece size for a project is usually the largest considering the following factors

bull Stability and stresses on the element during handling

bull Transportation size and weight regulations and equipment restrictions

Pre-Planning Piece SizePre-Planning Piece Size

bull Available crane capacity at both the plant and the project site

bull Position of the crane must be considered since capacity is a function of reach

bull Storage space truck turning radius and other site restrictions

Planning and SetupPlanning and Setup

bull Once a piece has been fabricated it is necessary to remove it from the mold without being damaged

bull Positive drafts or breakaway forms should be used to allow a member to lift away from the casting bed without becoming wedged within the form

bull Adequate draft also serves to reduce trapped air bubbles

Planning and SetupPlanning and Setup

bull Lifting points must be located to keep member stresses within limits and to ensure proper alignment of the piece as it is being lifted

bull Members with unsymmetrical geometry or projecting sections may require supplemental lifting points and auxiliary lifting lines to achieve even support during handling

bull ldquoCome-alongsrdquo or ldquochain-fallsrdquo are frequently used for these auxiliary lines

Planning and SetupPlanning and Setup

bull When the member has areas of small cross section or large cantilevers it may be necessary to add a structural steel ldquostrongbackrdquo to the piece to provide added strength

Planning and SetupPlanning and Setup

bull Members that require a secondary process prior to shipment such as sandblasting or attachment of haunches may need to be rotated at the production facility In these cases it may be necessary to cast in extra lifting devices to facilitate these maneuvers

Planning and SetupPlanning and Setup

bull When developing member shapes the designer should consider the extra costs associated with special rigging or forming and pieces requiring multiple handling

Stripping GeneralStripping General

bull Orientation of members during storage shipping and final in-place position is critical in determining stripping requirements

bull They can be horizontal vertical or some angle in betweenbull The number and location of lifting devices are chosen to keep stresses within

the allowable limits which depends on whether the ldquono crackingrdquo or ldquocontrolled crackingrdquo criteria is to be used

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

IntroductionIntroduction

bull The loads and forces on precast and prestressed concrete members during production transportation or erection will frequently require a separate analysis

bull Concrete strengths are lowerbull Support points and orientation are usually

different from members in their final position

Pre-Planning Piece SizePre-Planning Piece Size

The most economical piece size for a project is usually the largest considering the following factors

bull Stability and stresses on the element during handling

bull Transportation size and weight regulations and equipment restrictions

Pre-Planning Piece SizePre-Planning Piece Size

bull Available crane capacity at both the plant and the project site

bull Position of the crane must be considered since capacity is a function of reach

bull Storage space truck turning radius and other site restrictions

Planning and SetupPlanning and Setup

bull Once a piece has been fabricated it is necessary to remove it from the mold without being damaged

bull Positive drafts or breakaway forms should be used to allow a member to lift away from the casting bed without becoming wedged within the form

bull Adequate draft also serves to reduce trapped air bubbles

Planning and SetupPlanning and Setup

bull Lifting points must be located to keep member stresses within limits and to ensure proper alignment of the piece as it is being lifted

bull Members with unsymmetrical geometry or projecting sections may require supplemental lifting points and auxiliary lifting lines to achieve even support during handling

bull ldquoCome-alongsrdquo or ldquochain-fallsrdquo are frequently used for these auxiliary lines

Planning and SetupPlanning and Setup

bull When the member has areas of small cross section or large cantilevers it may be necessary to add a structural steel ldquostrongbackrdquo to the piece to provide added strength

Planning and SetupPlanning and Setup

bull Members that require a secondary process prior to shipment such as sandblasting or attachment of haunches may need to be rotated at the production facility In these cases it may be necessary to cast in extra lifting devices to facilitate these maneuvers

Planning and SetupPlanning and Setup

bull When developing member shapes the designer should consider the extra costs associated with special rigging or forming and pieces requiring multiple handling

Stripping GeneralStripping General

bull Orientation of members during storage shipping and final in-place position is critical in determining stripping requirements

bull They can be horizontal vertical or some angle in betweenbull The number and location of lifting devices are chosen to keep stresses within

the allowable limits which depends on whether the ldquono crackingrdquo or ldquocontrolled crackingrdquo criteria is to be used

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Pre-Planning Piece SizePre-Planning Piece Size

The most economical piece size for a project is usually the largest considering the following factors

bull Stability and stresses on the element during handling

bull Transportation size and weight regulations and equipment restrictions

Pre-Planning Piece SizePre-Planning Piece Size

bull Available crane capacity at both the plant and the project site

bull Position of the crane must be considered since capacity is a function of reach

bull Storage space truck turning radius and other site restrictions

Planning and SetupPlanning and Setup

bull Once a piece has been fabricated it is necessary to remove it from the mold without being damaged

bull Positive drafts or breakaway forms should be used to allow a member to lift away from the casting bed without becoming wedged within the form

bull Adequate draft also serves to reduce trapped air bubbles

Planning and SetupPlanning and Setup

bull Lifting points must be located to keep member stresses within limits and to ensure proper alignment of the piece as it is being lifted

bull Members with unsymmetrical geometry or projecting sections may require supplemental lifting points and auxiliary lifting lines to achieve even support during handling

bull ldquoCome-alongsrdquo or ldquochain-fallsrdquo are frequently used for these auxiliary lines

Planning and SetupPlanning and Setup

bull When the member has areas of small cross section or large cantilevers it may be necessary to add a structural steel ldquostrongbackrdquo to the piece to provide added strength

Planning and SetupPlanning and Setup

bull Members that require a secondary process prior to shipment such as sandblasting or attachment of haunches may need to be rotated at the production facility In these cases it may be necessary to cast in extra lifting devices to facilitate these maneuvers

Planning and SetupPlanning and Setup

bull When developing member shapes the designer should consider the extra costs associated with special rigging or forming and pieces requiring multiple handling

Stripping GeneralStripping General

bull Orientation of members during storage shipping and final in-place position is critical in determining stripping requirements

bull They can be horizontal vertical or some angle in betweenbull The number and location of lifting devices are chosen to keep stresses within

the allowable limits which depends on whether the ldquono crackingrdquo or ldquocontrolled crackingrdquo criteria is to be used

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Pre-Planning Piece SizePre-Planning Piece Size

bull Available crane capacity at both the plant and the project site

bull Position of the crane must be considered since capacity is a function of reach

bull Storage space truck turning radius and other site restrictions

Planning and SetupPlanning and Setup

bull Once a piece has been fabricated it is necessary to remove it from the mold without being damaged

bull Positive drafts or breakaway forms should be used to allow a member to lift away from the casting bed without becoming wedged within the form

bull Adequate draft also serves to reduce trapped air bubbles

Planning and SetupPlanning and Setup

bull Lifting points must be located to keep member stresses within limits and to ensure proper alignment of the piece as it is being lifted

bull Members with unsymmetrical geometry or projecting sections may require supplemental lifting points and auxiliary lifting lines to achieve even support during handling

bull ldquoCome-alongsrdquo or ldquochain-fallsrdquo are frequently used for these auxiliary lines

Planning and SetupPlanning and Setup

bull When the member has areas of small cross section or large cantilevers it may be necessary to add a structural steel ldquostrongbackrdquo to the piece to provide added strength

Planning and SetupPlanning and Setup

bull Members that require a secondary process prior to shipment such as sandblasting or attachment of haunches may need to be rotated at the production facility In these cases it may be necessary to cast in extra lifting devices to facilitate these maneuvers

Planning and SetupPlanning and Setup

bull When developing member shapes the designer should consider the extra costs associated with special rigging or forming and pieces requiring multiple handling

Stripping GeneralStripping General

bull Orientation of members during storage shipping and final in-place position is critical in determining stripping requirements

bull They can be horizontal vertical or some angle in betweenbull The number and location of lifting devices are chosen to keep stresses within

the allowable limits which depends on whether the ldquono crackingrdquo or ldquocontrolled crackingrdquo criteria is to be used

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Planning and SetupPlanning and Setup

bull Once a piece has been fabricated it is necessary to remove it from the mold without being damaged

bull Positive drafts or breakaway forms should be used to allow a member to lift away from the casting bed without becoming wedged within the form

bull Adequate draft also serves to reduce trapped air bubbles

Planning and SetupPlanning and Setup

bull Lifting points must be located to keep member stresses within limits and to ensure proper alignment of the piece as it is being lifted

bull Members with unsymmetrical geometry or projecting sections may require supplemental lifting points and auxiliary lifting lines to achieve even support during handling

bull ldquoCome-alongsrdquo or ldquochain-fallsrdquo are frequently used for these auxiliary lines

Planning and SetupPlanning and Setup

bull When the member has areas of small cross section or large cantilevers it may be necessary to add a structural steel ldquostrongbackrdquo to the piece to provide added strength

Planning and SetupPlanning and Setup

bull Members that require a secondary process prior to shipment such as sandblasting or attachment of haunches may need to be rotated at the production facility In these cases it may be necessary to cast in extra lifting devices to facilitate these maneuvers

Planning and SetupPlanning and Setup

bull When developing member shapes the designer should consider the extra costs associated with special rigging or forming and pieces requiring multiple handling

Stripping GeneralStripping General

bull Orientation of members during storage shipping and final in-place position is critical in determining stripping requirements

bull They can be horizontal vertical or some angle in betweenbull The number and location of lifting devices are chosen to keep stresses within

the allowable limits which depends on whether the ldquono crackingrdquo or ldquocontrolled crackingrdquo criteria is to be used

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Planning and SetupPlanning and Setup

bull Lifting points must be located to keep member stresses within limits and to ensure proper alignment of the piece as it is being lifted

bull Members with unsymmetrical geometry or projecting sections may require supplemental lifting points and auxiliary lifting lines to achieve even support during handling

bull ldquoCome-alongsrdquo or ldquochain-fallsrdquo are frequently used for these auxiliary lines

Planning and SetupPlanning and Setup

bull When the member has areas of small cross section or large cantilevers it may be necessary to add a structural steel ldquostrongbackrdquo to the piece to provide added strength

Planning and SetupPlanning and Setup

bull Members that require a secondary process prior to shipment such as sandblasting or attachment of haunches may need to be rotated at the production facility In these cases it may be necessary to cast in extra lifting devices to facilitate these maneuvers

Planning and SetupPlanning and Setup

bull When developing member shapes the designer should consider the extra costs associated with special rigging or forming and pieces requiring multiple handling

Stripping GeneralStripping General

bull Orientation of members during storage shipping and final in-place position is critical in determining stripping requirements

bull They can be horizontal vertical or some angle in betweenbull The number and location of lifting devices are chosen to keep stresses within

the allowable limits which depends on whether the ldquono crackingrdquo or ldquocontrolled crackingrdquo criteria is to be used

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Planning and SetupPlanning and Setup

bull When the member has areas of small cross section or large cantilevers it may be necessary to add a structural steel ldquostrongbackrdquo to the piece to provide added strength

Planning and SetupPlanning and Setup

bull Members that require a secondary process prior to shipment such as sandblasting or attachment of haunches may need to be rotated at the production facility In these cases it may be necessary to cast in extra lifting devices to facilitate these maneuvers

Planning and SetupPlanning and Setup

bull When developing member shapes the designer should consider the extra costs associated with special rigging or forming and pieces requiring multiple handling

Stripping GeneralStripping General

bull Orientation of members during storage shipping and final in-place position is critical in determining stripping requirements

bull They can be horizontal vertical or some angle in betweenbull The number and location of lifting devices are chosen to keep stresses within

the allowable limits which depends on whether the ldquono crackingrdquo or ldquocontrolled crackingrdquo criteria is to be used

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Planning and SetupPlanning and Setup

bull Members that require a secondary process prior to shipment such as sandblasting or attachment of haunches may need to be rotated at the production facility In these cases it may be necessary to cast in extra lifting devices to facilitate these maneuvers

Planning and SetupPlanning and Setup

bull When developing member shapes the designer should consider the extra costs associated with special rigging or forming and pieces requiring multiple handling

Stripping GeneralStripping General

bull Orientation of members during storage shipping and final in-place position is critical in determining stripping requirements

bull They can be horizontal vertical or some angle in betweenbull The number and location of lifting devices are chosen to keep stresses within

the allowable limits which depends on whether the ldquono crackingrdquo or ldquocontrolled crackingrdquo criteria is to be used

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Planning and SetupPlanning and Setup

bull When developing member shapes the designer should consider the extra costs associated with special rigging or forming and pieces requiring multiple handling

Stripping GeneralStripping General

bull Orientation of members during storage shipping and final in-place position is critical in determining stripping requirements

bull They can be horizontal vertical or some angle in betweenbull The number and location of lifting devices are chosen to keep stresses within

the allowable limits which depends on whether the ldquono crackingrdquo or ldquocontrolled crackingrdquo criteria is to be used

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stripping GeneralStripping General

bull Orientation of members during storage shipping and final in-place position is critical in determining stripping requirements

bull They can be horizontal vertical or some angle in betweenbull The number and location of lifting devices are chosen to keep stresses within

the allowable limits which depends on whether the ldquono crackingrdquo or ldquocontrolled crackingrdquo criteria is to be used

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stripping GeneralStripping General

bull It is desirable to use the same lifting devices for both stripping and erection however additional devices may be required to rotate the member to its final position

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stripping GeneralStripping General

bull Panels that are stripped by rotating about one edge with lifting devices at the opposite edge will develop moments as shown

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stripping GeneralStripping General

bull When panels are stripped this way care should be taken to prevent spalling of the edge along which the rotation occurs

bull A compressible material or sand bed will help protect this edge

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stripping GeneralStripping General

bull Members that are stripped flat from the mold will develop the moments shown

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stripping GeneralStripping General

bull In some plants tilt tables or turning rigs are used to reduce stripping stresses

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stripping GeneralStripping General

bull Since the section modulus with respect to the top and bottom faces may not be the same the designer must select the controlling design limitationbull Tensile stresses on both faces to be less than that which

would cause crackingbull Tensile stress on one face to be less than that which would

cause cracking with controlled cracking permitted on the unexposed face

bull Controlled cracking permitted on both faces

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stripping GeneralStripping General

bull If only one of the faces is exposed to view the exposed face will generally control the stripping method

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Rigging ConfigurationsRigging Configurations

bull Stresses and forces occurring during handling are also influenced by the type of rigging used to hook up to the member

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Rigging ConfigurationsRigging Configurations

bull Lift line forces for a two-point lift using inclined lines are shown

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Rigging ConfigurationsRigging Configurations

bull When the sling angle is small the components of force parallel to the longitudinal axis of the member may generate a significant moment due to secondary effects

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Rigging ConfigurationsRigging Configurations

bull While this effect can and should be accounted for it is not recommended that it be allowed to dominate design moments

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Rigging ConfigurationsRigging Configurations

bull Consideration should be given to using spreader beams two cranes or other mechanisms to increase the sling angle

bull Any such special handling required by the design should be clearly shown on drawings

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Rigging ConfigurationsRigging Configurations

bull Using a spreader beam can also eliminate the use of rolling blocks

bull Note that the spreader beam must be sufficiently stiffer than the concrete panel to limit panel deflections and cracking

bull Lifting hook locations hook heights and sling lengths are critical to ensure even lifting of the member

bull For analysis the panel acts as a continuous beam over multiple supports

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stripping DesignStripping Design

bull To account for the forces on the member caused by form suction and impact it is common practice to apply a multiplier to the member weight and treat the resulting force as an equivalent static service load

bull The multipliers cannot be quantitatively derived so they are based on experience

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stripping DesignStripping Design

bull PCI provides a table of typical values

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Factor of SafetyFactor of Safety

bull When designing for stripping and handling the following safety factors are recommendedndash Use embedded inserts and erection devices with a

pullout strength at least equal to four (4) times the calculated load on the device

ndash For members designed ldquowithout crackingrdquo the modulus of rupture (MOR) is divided by a safety factor of 15

75sdotλ sdot f c

15=5 sdotλ sdot f

c

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Stress limits for prestressed members during production are discussed in Section 4222 of the the PCI Handbook

bull ACI 318-02 does not restrict stresses on non-prestressed members but does specify minimum reinforcement spacing as discussed in Section 4221 (PCI chapter 4 member design)

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Stress Limits amp Crack ControlStress Limits amp Crack Control

bull Members which are exposed to view will generally be designed for the ldquono discernible cracking criteriardquo (see Eq 4222) which limits the stress to

bull In the case of stripping stresses fprimeci should be substituted for fprimec

bull Whether or not the members are exposed to view the strength design and crack control requirements of ACI 318-02 as discussed in Chapter 4 of this Handbook must be followed

5sdotλ sdot f

c

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Benefits of PrestressingBenefits of Prestressing

bull Panels can be prestressed using either pretensioning or post-tensioning

bull Design is based on Chapter 18 of ACI 318-02 as described in Chapter 4 of this Handbook Further tensile stresses should be restricted to less than must be followed

5sdotλ sdot f c

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Benefits of PrestressingBenefits of Prestressing

bull It is recommended that the average stress due to prestressing after losses be within a range of 125 to 800 psi

bull The prestressing force should be concentric with the effective cross section in order to minimize camber although some manufacturers prefer to have a slight inward bow in the in-place position to counteract thermal bow

bull It should be noted that concentrically prestressed members do not camber hence the form adhesion may be larger than with members that do camber

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Strand RecomendationStrand Recomendation

bull In order to minimize the possibility of splitting cracks in thin pretensioned members the strand diameter should not exceed that shown in the table below

bull Additional light transverse reinforcement may be required to control longitudinal cracking

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Strand RecommendationsStrand Recommendations

bull When wall panels are post-tensioned care must be taken to ensure proper transfer of force at the anchorage and protection of anchors and tendons against corrosion

bull Straight strands or bars may be used or to reduce the number of anchors the method shown may be used

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Strand RecommendationStrand Recommendation

bull It should be noted that if an unbonded tendon is cut the prestress is lost This can sometimes happen if an unplanned opening is cut in at a later date

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Handling DevicesHandling Devices

bull Since lifting devices are subject to dynamic loads ductility of the material is a requirement

bull Deformed reinforcing bars should not be used as the deformations result in stress concentrations from the shackle pin

bull Also reinforcing bars may be hard grade or re-rolled rail steel with little ductility and low impact strength at cold temperatures

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Handling DevicesHandling Devices

bull Strain hardening from bending may cause embrittlement

bull Smooth bars of a known steel grade may be used if adequate embedment or mechanical anchorage is provided

bull The diameter must be such that localized failure will not occur by bearing on the shackle pin

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Aircraft Cable LoopsAircraft Cable Loops

bull For smaller precast members aircraft cable can be used for stripping and erection purposes

bull Aircraft cable comes in several sizes with different capacities

bull The flexible cable is easier to handle and will not leave rust stains on precast concrete

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Aircraft Cable LoopsAircraft Cable Loops

bull For some small precast members such as coping the flexible loops can be cast in ends of members and tucked back in the joints after erection

bull Aircraft cable loops should not be used as multiple loops in a single location as even pull on multiple cables in a single hook is extremely difficult to achieve

bull User should ensure that the cable is clean and that each leg of the loop is embedded a minimum of 48 in

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Prestressing Strand LoopsPrestressing Strand Loops

bull Prestressing strand both new and used may be used for lifting loops

bull The capacity of a lifting loop embedded in concrete is dependent upon the strength of the strand length of embedment the condition of the strand the diameter of the loop and the strength of the concrete

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Prestressing Strand LoopsPrestressing Strand Loops

bull As a result of observations of lift loop behavior during the past few years it is important that certain procedures be followed to prevent both strand slippage and strand failure

bull Precast producersrsquo tests andor experience offer the best guidelines for the load capacity to use

bull A safety factor of 4 against slippage or breakage should be used

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Strand Loops RecommendationsStrand Loops Recommendations

bull In lieu of test data the recommendations listed below should be considered when using strand as lifting loopsndash Minimum embedment for each leg of the loop

should be 24 inndash The strand surface must be free of contaminants

such as form oil grease mud or loose rust which could reduce the bond of the strand to the concrete

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Strand Loops RecommendationsStrand Loops Recommendations

bull Continuedndash The diameter of the hook or fitting around

which the strand lifting eye will be placed should be at least four times the diameter of the strand being used

ndash Do not use heavily corroded strand or strand of unknown size and strength

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Strand Loops RecommendationsStrand Loops Recommendations

bull In the absence of test or experience it is recommended that the safe load on a single 12 in diameter 270 ksi strand loop satisfying the above recommendations not exceed 8 kips

bull The safe working load of multiple loops may be conservatively obtained by multiplying the safe load for one loop by 17 for double loops and 22 for triple loops

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Strand Loops RecommendationsStrand Loops Recommendations

bull To avoid overstress in one loop when using multiple loops care should be taken in the fabrication to ensure that all strands are bent the same

bull Thin wall conduit over the strands in the region of the bend has been used to reduce the potential for overstress

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Strand Loops RecommendationsStrand Loops Recommendations

bull When using double or triple loops the embedded ends may need to be spread apart for concrete consolidation around embedded ends without voids being formed by bundled strand

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Threaded InsertsThreaded Inserts

bull Threaded inserts can have NC (National Course) or coil threads

bull Anchorage is provided by loop strut or reinforcing bar

bull Inserts must be placed accurately because their safe working load decreases sharply if they are not perpendicular to the bearing surface or if they are not in a straight line with the applied force

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Threaded InsertsThreaded Inserts

bull Embedment of inserts close to an edge will greatly reduce the effective area of the resisting concrete shear cone and thus reduce the tension safe working load of the embedded insert

bull When properly designed for both insert and concrete capacities threaded inserts have many advantages

bull However correct usage is sometimes difficult to inspect during handling operations

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Threaded InsertsThreaded Inserts

bull In order to ensure that an embedded insert acts primarily in tension a swivel plate as indicated in should be used

bull It is extremely important that sufficient threads be engaged to develop the strength of the bolt

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Threaded InsertsThreaded Inserts

bull For straight tension loads only eye bolts or wire rope loops provide a fast method for handling precast members

bull Do not use either device if shear loading conditions exist

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Proprietary DevicesProprietary Devices

bull A variety of castings or stock steel devices machined to accept specialized lifting assemblies are used in the precast industry

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Proprietary DevicesProprietary Devices

bull These proprietary devices are usually recessed (using a ldquopocket formerrdquo) to provide access to the lifting unit The recess allows one panel to be placed against another without cutting off the lifting device and also helps prevent spalling around the device

bull Longer devices are used for edge lifting or deep precast concrete members

bull Shallow devices are available for thin precast concrete members

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Proprietary DevicesProprietary Devices

bull The longer devices usually engage a reinforcing bar to provide greater pullout capacity and often have holes for the bar to pass through as shown to the left

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Proprietary DevicesProprietary Devices

bull These units have a rated capacity as high as 22 tons with reductions for thin panels or close edge distances

bull Supplemental reinforcement may be required to achieve these values

bull Shallow units usually have a spread foot or base to increase pullout capacity

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Proprietary DevicesProprietary Devices

bull Reinforcing bars are required in two directions over the base to fully develop the lifting unit as shown in Figure below

bull These inserts are rated up to 8 tons

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Proprietary DevicesProprietary Devices

bull Some lifting eyes do not swivel so rotation may be a concern

bull In all cases manufacturer recommendations should be rigorously followed when using any of these devices

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Wall Panel ExampleWall Panel Example

bull This example and others in Chapter 5 illustrate the use of many of the recommendations in this chapter

bull They are intended to be illustrative and general onlybull Each manufacturer will have its own preferred

methods of handling

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Wall Panel ExampleWall Panel Example

GivenA flat panel used as a loadbearing wall on a two-story structure as shown on next slideSection properties (nominal dimensions are used for design)

Solid panel Panel with openingsA = 960 in2 A = 480 in2

Sb = St = 1280 in3 Sb = St = 640 in3

Ix = 5120 in4 Ix = 2560 4 in4

Unit weight 150 pcf = 100 psf = 0100 ksf Total weight = 352 kips (solid panel)

= 292 kips (panel w openings)

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Wall Panel ExampleWall Panel Example

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Wall Panel ExampleWall Panel Example

bull Stripping methodndash Inside crane height prevents panel from being

turned on edge directly in mold therefore strip flat

bull Handling multipliersndash Exposed flat surface has a smooth form finish with

false joints Side rails are removable Use multiplier of 14

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Wall Panel ExampleWall Panel Example

bull fprimeci at stripping = 3000 psibull Allowable tensile stresses at stripping and lifting

ProblemCheck critical stresses involved with stripping Limit stresses to 0274 ksi

Compare Simple Solution to Mechanics Solution

5sdotλ sdot f

c=5 sdot(10) sdot 3000psi

1000=0274ksi

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Solution StepsSolution Steps

Step 1 ndash Determine section propertiesStep 2 ndash Select number of pick points and

determine maximum stressStep 3 ndash Determine stress from mechanic

approachStep 4 ndash Check panel with openingStep 5 ndash Check rolling block solutionStep 6 ndash Check transverse bendingStep 7 ndash Check secondary effects

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 1 ndash Determine Section PropertiesStep 1 ndash Determine Section Properties

Solid panel dimensionsa = 10 ft b = 352 ft a2 = 5 ft = 60 in

S for resisting section (half of panel width)

bsdoth2

6=60 insdot(8 in)2

6=640 in3

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 2 ndash 4-point pickStep 2 ndash 4-point pick

Figure 53611(a) (page 5-5)

My=00107 sdotwsdotasdotb2

=00107 010( ) 10( ) 352ft( )212( ) 14( ) =223kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 2 ndash Check StressesStep 2 ndash Check Stresses

4 Point Stresses

Not Good try 8 point pick

ft=f

b=223 kipminusin

640 in3=0348 ksi gt 0274 ksi

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 2 ndash 8 Point PickStep 2 ndash 8 Point Pick

Figure 5311(b) (Page 5-5)

My=00027 sdotwsdotasdotb2

=00027 010( ) 10( ) 352ft( )212( ) 14( ) =562kip in

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 2 ndash Check StressesStep 2 ndash Check Stresses

8 Point Stresses

ft=f

b=562 kipminusin

640 in3=0088 ksi lt 0274 ksi

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 3 ndash Mechanics of MaterialsStep 3 ndash Mechanics of Materials

minusMmax

=wsdotl 2

2=minus10 sdot 365( )

2

2 =minus67ft minuskip

+Mmax

=area under shear diagram

=minus67 +12

515( )103ft

2 =+67kipsdotft

ft=67 14( ) 12( )

1280=0088 ksi lt 0274 ksi

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 4 ndash Panel With OpeningsStep 4 ndash Panel With Openings

ft=68 14( ) 12( )

1280=0089ksi

or ft=59 14( ) 12( )

640in3

=0155 ksi lt 0274 ksi OK

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 5 ndash Rolling BlocksStep 5 ndash Rolling Blocks

bull If using a rolling block for handling as shown below the panel cannot be analyzed with the previous method

bull Each leg of continuous cable over a rolling block must carries equal load

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 5 ndash Rolling BlockStep 5 ndash Rolling Block

w =292kips

RL=292 84( )

93 + 84=139 kips

R1=R

2=1392

=70 kips

RR=292 minus139 =153 kips

R1=R

2=1532

=76 kips

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

bull Consider lower portion of panel with openingsbull Note that Figure Without the concrete in the area of the

opening the weight is reduced and unevenly distributed Also the resisting section is limited to a width of 47 ft

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 6 ndash Transverse BendingStep 6 ndash Transverse Bending

Section through lifters

From continuous beam analysis load carried by bottom two anchors is 72 kips therefore

w

2= 47( ) 067( ) 015( ) =047 kips

ft

w1=72 minus 047( ) 5( )

2 25( )=097 kips

ft

Mmax

=21 ft minuskips =252 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Check added moment due to sling angle

Using recessed proprietary lifting anchor

e = 35 in

sling angle φ =60o

P =72 kips

2=36 kips

Mz=36 sdot

35tan60o

⎛

⎝⎜⎞

⎠⎟=73 kips

Mtotal

=253 + 73 =325 inminuskips

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 7 ndash Secondary EffectsStep 7 ndash Secondary Effects

Resisting Section

Therefore Section is OK

S =bsdott2

6=56 8( )

2

6=597in3

f =M

totalsdothandling mult( )

S=

325( ) 14( )

597in3

=008 ksi lt 0274 ksi

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Prestressed Wall ExamplePrestressed Wall Example

Given

Same wallpanel as previousexample

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Prestressed Wall ExamplePrestressed Wall Example

Problem

Determine required number of 12 in diameter 270 ksi strands pulled to 289 kips to prevent cracking in window panel Assume 10 loss of prestressFrom previous example tensile stress is 0431 ksi The desired level of tensile stress is or 0274 ksi5 3000 psisdot

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Solution StepsSolution Steps

Step 1 ndash Determine additional compressive Required

Step 2 ndash Determine the number of strands required based on stress

Step 3 ndash Calculate the number of strands

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 1 ndash Additional CompressiveStep 1 ndash Additional Compressive

Compressive stress required 0431 ndash 0274 = 0157 ksi

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 2 ndash Of Strands Based On StressStep 2 ndash Of Strands Based On Stress

From previous the max momentstress occurs at lifting points (-M) This results in tensile stresses on the top face

A = 2( ) 30( ) 725( ) =435 in2

St=

2( ) 30( ) 725( )2

6=526 in3

P

A=

no of strand( ) 289( ) 090( )

435in2=0060 no of strand( ) ksi( )

M

S=

no of strand( ) 289( ) 090( )7252

minus4⎛

⎝⎜⎞

⎠⎟

526 =0019 no of strand( ) ksi( )

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Step 3 ndash Number of StrandsStep 3 ndash Number of Strands

0060(no of strands) ndash 0019(no of strands) = 0157 ksi

No of strands = 38

Add four strands to panel (two on each side of opening)

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

StorageStorage

bull Wherever possible a member should be stored on points of support located at or near those used for stripping and handling

bull Where points other than those used for stripping or handling are used for storage the storage condition must be checked

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

StorageStorage

bull If support is provided at more than two points and the design is based on more than two supports precautions must be taken so that the element does not bridge over one of the supports due to differential support settlement

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

StorageStorage

bull Warpage in storage may be caused byndash temperature or shrinkage differential between

surfacesndash creep ndash storage conditions

bull Warpage can only be minimized by providingbull Where feasible the member should be

oriented in the yard so that the sun does not overheat one side

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

StorageStorage

bull By superposition the total instantaneous deflection ymax at the maximum point can be estimated by

y

max=1875 w( ) sdotsinθ

Eci

sdota4

Ic

+l 4

Ib

⎡

⎣⎢⎢

⎤

⎦⎥⎥

Ic Ib = moment of inertia of uncracked section in the respective directions for 1 in width of panel

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

StorageStorage

bull This instantaneous deflection should be modified by a factor to account for the time dependent effects of creep and shrinkage

bull ACI 318-02 suggests the total deformation yt at any time can be estimated as

y

t=y

maxtimes 1 + λ( )

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

StorageStorage

bull λ = amplification due to creep and shrinkage as a function of primeρ (reinforcement ratio for non-prestressed compressionreinforcementAsbt)

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

TransportationTransportation

bull The method used for transport can affect the structural design because of size and weight limitations and the dynamic

bull Except for long prestressed deck members most products are transported on either flatbed or low-boy trailers

bull Trailers deform during hauling bull Size and weight limitations vary from one state

to state bull Loads are further restricted on secondary roadsbull The common payload for standard trailers

without special permits is 20 tons

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

TransportationTransportation

bull Low-boy trailers permit the height to be increased to about 10 to 12 ft bull However they have a have a shorter bed length bull This height may require special routing to avoid low overpasses and overhead wires

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

TransportationTransportation

bull Erection is simplified when members are transported in the same orientation they will have in the structure

bull For example single-story wall panels can be transported on A-frames with the panels uprightbull A-frames also provide good lateral support and the desired two points of vertical support

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

TransportationTransportation

bull Longer units can be transported on their sides to take advantage of the increased stiffness compared with flat shipment

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

TransportationTransportation

bull In all cases the panel support locations should be consistent with the panel designbull Panels with large openings sometimes require strongbacks braces or ties to keep

stresses within the design values

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

TransportationTransportation

bull For members not symmetrical with respect to the bending axis the following expressions can be used for determining the location of supports to give equal tensile stresses for positive and negative bending moments

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

TransportationTransportation

bull For one end cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =12

1 +y

b

yt

minus 1 +y

b

yt

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

TransportationTransportation

bull For two ends cantileveredhellip

Whereyb = distance from the bending axis to the bottom fiber

yt = distance from the bending axis to the top fiber

x =1

2 sdot 1 + 1 +y

t

yb

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

ErectionErection

bull Precast concrete members frequently must be reoriented from the position used to transport to its final construction position

bull The analysis for this ldquotrippingrdquo (rotating) operation is similar to that used during other handling stages

bull In chapter 5 in the PCI handbook maximum moments for several commonly used tripping techniques are illustrated

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Tripping Design GuideTripping Design Guide

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

ErectionErection

bull When using two crane lines the center of gravity must be between them in order to prevent a sudden shifting of the load while it is being rotated

bull To ensure that this is avoided the stability condition shown must be met

e gt

l

2minus

l 2 minusb2

2minusa

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

ErectionErection

bull The capacities of lifting devices must be checked for the forces imposed during the tripping operation since the directions vary

bull When rotating a panel with two crane lines the pick points should be located to prevent the panel from an uncontrolled roll on the roller blocks can be done by slightly offsetting the pick point locations to shift the weight toward the upper crane line lift points or by using chain drags on the rolling block

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erecting Wall Panels ExampleErecting Wall Panels Example

GivenThe wall panels with openings used on previous examples

ProblemDetermine appropriate procedures for erecting the wall panels with openings panel will be shipped flat

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erecting Wall Panels ExampleErecting Wall Panels Example

Assumptionsbull Limit stresses to (0354 ksi)bull Crane has main and auxiliary linesbull A telescoping man lift is available on site

Solutionbull Try three-point rotation up using stripping inserts and

rolling block To simplify conservatively use solid panel (no openings) to determine moments

5 f

c

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erecting Wall Panels ExampleErecting Wall Panels Example

W =10kips ft

RB=

3517( ) 1( )35172

⎛

⎝⎜⎞

⎠⎟

3517 0604 +02922

⎛

⎝⎜⎞

⎠⎟

=234 kips

RB1

=RB2

=117 kips

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erecting Wall Panels ExampleErecting Wall Panels Example

In Horizontal Position

Therefore 3 point pick not adequate

R

T= 3517( ) 1( ) minus234kips =118kips

MMAX

=696kipsdotft =8352kipsdotin

f =12(8352kipsdotin)

635=158 ksi gt 0354 ksi

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Knowing from the stripping analysis that a four-point pick can be used the configurations shown here may be used

bull However this rigging may become unstable at some point during tripping ie continued rotation without tension in Line A

bull Therefore the lower end of the panel must stay within inches of the ground to maintain control

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erecting Wall Panels ExampleErecting Wall Panels Example

bull Because the previous configuration requires six rolling blocks and can be cumbersome the method shown on the following slide may be an alternative

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erecting Wall Panels ExampleErecting Wall Panels Example

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erection Bracing IntroductionErection Bracing Introduction

bull This section deals with the temporary bracing which may be necessary to maintain structural stability of a precast structure during construction

bull When possible the final connections should be used to provide at least part of the erection bracing but additional bracing apparatus is sometimes required to resist all of the temporary loads

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erection Bracing IntroductionErection Bracing Introduction

bull These temporary loads may include wind seismic eccentric dead loads including construction loads unbalanced conditions due to erection sequence and incomplete connections Due to the low probability of design loads occurring during erection engineering judgment should be used to establish a reasonable design load

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull Proper planning of the construction process is essential for efficient and safe erection

bull Sequence of erection must be established early and the effects accounted for in the bracing analysis and the preparation of shop drawings

bull The responsibility for the erection of precast concrete may vary as followsndash (see also ACI 318-02 Section 103)

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The precast concrete manufacturer supplies the product erected either with his own forces or by an independent erector

bull The manufacturer is responsible only for supplying the product FOB plant or jobsite

bull Erection is done either by the general contractor or by an independent erector under a separate agreement

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The products are purchased by an independent erector who has a contract to furnish the complete precast concrete package

bull Responsibility for stability during erection must be clearly understood

bull Design for erection conditions must be in accordance with all local state and federal regulations It is desirable that this design be directed or approved by a Professional Engineer

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structurebull The erection drawings should also address the stability of

the structure during construction and include temporary connections

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

bull It is desirable that this design be directed or approved by a Professional Engineer

bull Erection drawings define the procedurebull on how to assemble the components into the final

structure

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull The erection drawings should also address the stability of the structure during construction and include temporary connections

bull When necessary special drawings may be required to include shoring guying bracing and specific erection sequences

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Erection Bracing ResponsibilitiesErection Bracing Responsibilities

bull For large andor complex projects a pre-job conference prior to the preparation of erection drawings may be warranted in order to discuss erection methods and to coordinate with other trades

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Handling EquipmentHandling Equipment

bull The type of jobsite handling equipment selected may influence the erection sequence and hence affect the temporary bracing requirements

bull Several types of erection equipment are available including truck-mounted and crawler mobile cranes hydraulic cranes tower cranes monorail systems derricks and others

bull The PCI Recommended Practice for Erection of Precast Concrete provides more information on the uses of each

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Surveying and LayoutSurveying and Layout

bull Before products are shipped to the jobsite a field check of the project is recommended to ensure that prior construction is suitable to accept the precast units

bull This check should include location line and grade of bearing surfaces notches blockouts anchor bolts cast-in hardware and dimensional deviations

bull Site conditions such as access ramps overhead electrical lines truck access etc should also be checked

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Surveying and LayoutSurveying and Layout

bull Any discrepancies between actual conditions and those shown on drawings should be addressed before erection is started

bull Surveys should be required before during and after erectionndash Before so that the starting point is clearly established and any potential difficulties with the support structure are determined earlyndash During to maintain alignmentndash After to ensure that the products have been erected within tolerances

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Loads on StructureLoads on Structure

bull The publication Design Loads on Structures During Construction (SEIASCE 37-02) provides minimum design loads including wind earthquake and construction loads and load combinations for partially completed structures and structures used during construction

bull In addition to working stress or strength design using loads from the above publication the designer must consider the effect of temporary loading on stability and bracing design

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Temporary Loading ExamplesTemporary Loading Examples

bull Columns with eccentric loads from other framing members produce sidesway which means the columns lean out of plumb

bull A similar condition can exist whencladding panels are erected on oneside of a multistory structure

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Temporary Loading ExamplesTemporary Loading Examples

bull Unbalanced loads due to partially complete erection may result in beam rotation

bull The erection drawings should address these Conditions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Temporary Loading ExamplesTemporary Loading Examples

bull Some solutions arendash Install wood wedges

between flange of tee and top of beam

ndash Use connection to columns that prevent rotation

ndash Erect tees on both sides of beam

ndash Prop tees to level below

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Temporary Loading ExamplesTemporary Loading Examples

bull Rotations and deflections of framing members may be caused by cladding panels This may result in alignment problems and require connections that allow for alignment adjustment after all panels are erected

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Temporary Loading ExamplesTemporary Loading Examples

bull If construction equipment such as concrete buggies man-lifts etc are to be used information such as wheel loads and spacing should be conveyed to the designer of the precast members and the designer of the erection bracing

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Factors of SafetyFactors of Safety

bull Suggested safety factors are shown

Bracing inserts cast into precast members 3

Reusable hardware 5

Lifting inserts 4

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Bracing Equipment and MaterialsBracing Equipment and Materials

bull For most one-story and two-story high components that require bracing steel pipe braces similar to those shown are used

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Proper anchoring of the braces to the precast members and deadmen must be considered

bull When the pipe braces are in tension there may be significant shear and tension loads applied to the deadmen

bull Properly designed deadmen are a requirement for safe bracing

bull Cable guys with turnbuckles are normally used for taller structures

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

Bracing Equipment and MaterialsBracing Equipment and Materials

bull Since wire rope used in cable guys can resist only tension they are usually used in combination with other cable guys in an opposite direction

bull Compression struts which may be the precast concrete components are needed to complete truss action of the bracing system

bull A number of wire rope types are availablebull Note that capacity of these systems is often

governed by the turnbuckle capacity

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

General ConsiderationsGeneral Considerations

bull Careful planning of the erection sequence is importantbull This plan is usually developed by a coordinated effort

involving the general contractor precast erector precaster production and shipping departments and a structural engineer

bull A properly planned erection sequence can reduce bracing requirements

bull For example with wall panel systems a corner can first be erected so that immediate stability can be achieved

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

General ConsiderationsGeneral Considerations

bull Similar considerations for shear wall structures can also reduce bracing requirements

bull All parties should be made aware of the necessity of closely following erection with the welded diaphragm connections

bull This includes the diaphragm to shear wall connections

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

General ConsiderationsGeneral Considerations

bull In order for precast erection to flow smoothlyndash The site access and preparation must be readyndash The to-be-erected products must be readyndash Precast shipping must be plannedndash The erection equipment must be readyndash Bracing equipment and deadmen must be ready

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions

QuestionsQuestions

• PCI 6th Edition
• Presentation Outline
• Introduction
• Pre-Planning Piece Size
• Slide 5
• Planning and Setup
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Stripping General
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Rigging Configurations
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Stripping Design
• Slide 26
• Factor of Safety
• Stress Limits amp Crack Control
• Slide 29
• Benefits of Prestressing
• Slide 31
• Strand Recomendation
• Strand Recommendations
• Strand Recommendation
• Handling Devices
• Slide 36
• Aircraft Cable Loops
• Slide 38
• Prestressing Strand Loops
• Slide 40
• Strand Loops Recommendations
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Threaded Inserts
• Slide 47
• Slide 48
• Slide 49
• Proprietary Devices
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Wall Panel Example
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Solution Steps
• Step 1 ndash Determine Section Properties
• Step 2 ndash 4-point pick
• Step 2 ndash Check Stresses
• Step 2 ndash 8 Point Pick
• Slide 66
• Step 3 ndash Mechanics of Materials
• Step 4 ndash Panel With Openings
• Step 5 ndash Rolling Blocks
• Step 5 ndash Rolling Block
• Step 6 ndash Transverse Bending
• Slide 72
• Step 7 ndash Secondary Effects
• Slide 74
• Prestressed Wall Example
• Slide 76
• Slide 77
• Step 1 ndash Additional Compressive
• Step 2 ndash Of Strands Based On Stress
• Step 3 ndash Number of Strands
• Storage
• Slide 82
• Slide 83
• Slide 84
• Slide 85
• Slide 86
• Transportation
• Slide 88
• Slide 89
• Slide 90
• Slide 91
• Slide 92
• Slide 93
• Slide 94
• Erection
• Tripping Design Guide
• Slide 97
• Slide 98
• Erecting Wall Panels Example
• Slide 100
• Slide 101
• Slide 102
• Slide 103
• Slide 104
• Slide 105
• Erection Bracing Introduction
• Slide 107
• Erection Bracing Responsibilities
• Slide 109
• Slide 110
• Slide 111
• Slide 112
• Slide 113
• Slide 114
• Handling Equipment
• Surveying and Layout
• Slide 117
• Loads on Structure
• Temporary Loading Examples
• Slide 120
• Slide 121
• Slide 122
• Slide 123
• Factors of Safety
• Bracing Equipment and Materials
• Slide 126
• Slide 127
• General Considerations
• Slide 129
• Slide 130
• Questions