structural design occupancy or use uniform (psf) concentrated (lbs) · 2005-05-12 · occupancy or...

Agricultural Hall and Annex

East Lansing, MI

2005 Senior Thesis

9

Structural Design

Gravity Loads

1- Based on US Standards

Occupancy or Use Uniform (psf) Concentrated (lbs)

Office building

-Office

-Lobbies and first-floor

corridors

-Corridor above first floor

-Partitions

-Superimposed

50

100

80

20

15

2000

2000

2000

2- Based on British Standards

Occupancy or Use Uniform (KN/m2) Concentrated

-General Office

-Partitions

2.5 KN/m2(52.2 psf)

1 KN/ m2(20.5 psf)

2.7 KN ( 607 lbs)

Load Combinations

Based on US Standards

1- U = 1.4(D+F)

2- U = 1.2(D+F+T) + 1.6 (L+H) + 0.5 (Lr or S or R)

3- U = 1.2D + 1.6(Lr or S or R) + (1.0l or 0.8W)

4- U = 1.2D + 1.6W + 1.0L +0.5(Lr or S or R)

5- U = 1.2D + 1.0E+ 1.0L + 0.2S

6- U = 0.9D +1 .6W + 1.6H

7- U = 0.9D + 1.0 E + 1.6 H

Based on British Standards

Condition

Dead + imposed load

( + earth pressure)

1.4 Gk + 1.6 Qk + 1.4 En

Dead + wind load

( + earth pressure)

1.4 ( Gk + Wk + En)

Design

loads

Dead + imposed + wind

load (+ earth pressure)

1.2 ( Gk + Qk + Wk + En)


East Lansing, MI

2005 Senior Thesis

10

Framing Systems

All the gravity systems except the one-way skip joist were designed using

equivalent frame method as it is described below. ADOSS was used to design the flat

slab with drop panels systems and the two-way slab with beams since it uses equivalent

frame method in the design.

Equivalent Frame Method (EFM)

According to ACI 318-02

13.7: The equivalent frame method involves the representation of the three-dimensional

slab system by a series of two-dimensional frames that are then analyzed for loads

acting in the plane of the frames. The negative and positive moments are

determined at the critical sections of the frame and then distributed to the slab

sections: column strips, beams if used, and middle strips. The equivalent frame

consists of three parts: Slab beams, columns, and torsional members.

13.7.2: Equivalent Frame

Each frame contains a row of columns and broad continuous beams. The beams or

slab beam includes the portion of the slab bounded by panel centerline on either

side of the column, together with the column-line beams or drop panel if used.

For the vertical loading, each floor with its columns may be analyzed separately.

It is convenient and sufficiently accurate to assume that the continuous frame is

completely fixed at support when computing the bending moment at the support.

Frames adjacent and parallel to an edge shall be bounded by the edge and the

centerline of adjacent panel.

Each frame can be analyzed separately.

13.7.3: Slab-beams

It is permitted to use the gross area of concrete when computing the moment of

inertia of slab-beams at any cross section outside of joints or column capitals.

Variation in moment of inertia along axis of slab-beams shall be taken into

account.

Moment of inertia of slab-beams from center of column to face of column,

bracket, or capital shall be assumed equal to the moment of inertia of the slab-

beam at face of column, bracket divided by (1-c2/l2)2.

13.7.4: Column

It is permitted to use the gross area of concrete when computing the moment of

inertia of slab-beams at any cross section outside of joints or column capitals

Variation in moment of inertia along axis of slab-beams shall be taken into

account.


East Lansing, MI

2005 Senior Thesis

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Moment of inertia of columns from top to bottom of the slab-beam at a joint shall

be assumed to be infinite.

13.7.5: Torsional Members

Tensional members shall be assumed to have a constant cross section throughout

their length consisting of the largest of: 1- portion of slab having a width equal to

column/capital width, 2- same portion of slab + transverse beam, or 3- transverse

beam.

Equivalent Frame Analysis by Computer

The EFM is oriented toward analysis using the method of moment distribution.

Plane frame analysis programs can be used for slab analysis based on the concepts of the

equivalent frame method, but the frame must be specially modeled. Variable moments of

inertia along the axis of slab-beams and columns require nodal points (continuous joints)

between sections where I is to be considered constant. It is also necessary to compute Kec

for each column, and then to compute the equivalent value of the moment of inertia for

the column. Alternately, a three-dimensional frame analysis maybe used in which the

torsional properties of the transverse supporting beam may be included directly. The third

option is to make used of specially written computer programs. The most widely used

program is Analysis and Design of Reinforced Concrete Slab System, ADOSS,

developed by Portal Cement Association (Nilson, Darwin, and Dolan, 2002). All the

systems for the submission are designed using ADOSS.

ADOSS Analysis

Procedure Steps

1- Enter project name and span ID

2- Choose type of slab and frame location, either exterior of interior

3- Number of spans. Spans are measured from center of column to center of

column. For 3 spans building, number of spans are 5 because ADOSS

considers the projection after column line as cantilever. Also, minimum slab

thickness is entered.

4- Choose material properties: 150 pcf for density, 4 ksi for f’c, and 60 ksi for fy.

5- Enter slab reinforcement data, can either be accepted or changed if desired.

6- Enter slab geometry. For the end span, the length is equal to the ½ column

width.

7- Enter column information, c1, c2, and column height above and below slab.

This is just an initial estimate for column size. All the columns have the same

sizes. Yet, they can be changed if required.

8- Enter the initial size of transverse beams for the end spans or middle spans.

Also the right eccentricity value must be entered so the beams edges coincide

with column and slab edges.


East Lansing, MI

2005 Senior Thesis

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9- Enter LL and DL loads. The dead load is only the superimposed load. Partial

loads can be entered as well if any.

10- Load factors can be changed if desired.

11- Column fixity factor is 100 %

12- Finally, design the system.

13- Check if everything is ok with the design such as shear, and deflection.

14- Redesign the system if necessary such as increasing slab thickness, and drop

panel thickness.

15- Redesign the system

16- Check the system to make sure that everything is ok.

ADOSS load patterns:

1- Full dead and 75 % live on adjacent spans

2- Full dead and 75 % live on odd-numbered spans.

3- Full dead and 75 % live on even-numbered spans

4- Full dead and full live on all spans

Wide-Module Concrete Joist System (Skip Joist System)

Skip Joist System is widely known as Wide-Module Concrete Joist System which

a joist system is having clear spacing between ribs of more than 30”. Skip Joist is

basically designed as T-beams according to ACI 8.10.

Maximum Bar size for single bars in the bottom of a wide-module joist rib

Rib Width at Bottom Stirrup

Style

No. of Bars

6” 7” 8” 9” 10”

2 #6 #9 #11 #14 #14 J

3 - #4 #6 #8 #10

2 #4 #8 #10 #11 #14 U

3 - - #5 #8 #9

Maximum Bar size for 2-bar bundles in the bottom of a wide-module joist rib

Rib Width at Bottom Stirrup

Style

No. of Bars

6” 7” 8” 9” 10”

1 #9 #11 #11 #11 #11 J

2 #3 #5 #6 #8 #9

1 #8 #11 #11 #11 #11 U

2 - #4 #5 #7 #8


East Lansing, MI

2005 Senior Thesis

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Design Consideration

1- ACI 7.7.1: Minimum concrete cover: 1 ½ in to stirrups and main flexural bars.

2- ACI 11.3.1.1: Design shear strength: Vc = 2 f’c bw d

3- ACI 11.5.5.3: Minimum shear reinforcement: Av= 50(bws)/fy

4- Reinforcing steel requirements and recommended details

Figure 3 Figure 4

Figure 5


East Lansing, MI

2005 Senior Thesis

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Figure 6 – Bar cutoff for Wide-Module One way Joist

Openings in Slab Systems

Based on US and British Standards

Since all my openings are large and interrupt the steel reinforcement in the

column strips, beams shall be designed around the openings to meet the design strength

and ductility requirements.

Deflection Check

For each designed system, the deflection was checked to make sure that it does

not exceed the maximum deflection that is set by the US or British Standards. All the

deflections that were obtained are mentioned later in the report. The material and

reinforcement properties are given below. Appendix A has all the maximum deflections

allowed by both US and British Standards.

Material Properties and Reinforcement

CONCRETE FACTORS SLABS BEAMS COLUMNS

DENSITY(pcf ) 150.0 150.0 150.0

TYPE NORMAL WGT NORMAL WGT NORMAL WGT

f'c (ksi) 4.0 4.0 4.0

fct (psi) 423.7 423.7 423.7

fr (psi) 474.3 474.3 474.3

REINFORCEMENT DETAILS: NON-PRESTRESSED

YIELD STRENGTH (flexural) Fy = 60.00 ksi

YIELD STRENGTH (stirrups) Fyv = 60.00 ksi

DISTANCE TO RF CENTER FROM TENSION FACE:

AT SLAB TOP = 1.50 in OUTER LAYER

AT SLAB BOTTOM = 1.50 in OUTER LAYER


East Lansing, MI

2005 Senior Thesis

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AT BEAM TOP = 1.50 in OUTER LAYER

AT BEAM BOTTOM = 1.50 in

FLEXURAL BAR SIZES: MINIMUM | MAXIMUM

AT SLAB TOP = # 4

AT SLAB BOTTOM = # 4

AT BEAM TOP = # 4 #14

IN BEAM BOTTOM = # 4 #14

MINIMUM SPACING:

IN SLAB = 6.00 in

IN BEAM = 1.00 in


East Lansing, MI

2005 Senior Thesis

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Wide Module One-way Joist

The wide module one-way joist system for the Agricultural Hall and Annex is

designed using the CRSI Handbook. There were several trials of wide module joists in

order to match the depth of the girder with the depth of the joist for more economical

system and efficient system. The best joist that matched the girder’s depth is 66” Forms +

6” Ribs @ 72 c.-c, the total depth = 24.5 in (20” Deep Rib + 4.5” Top Slab). All the

girders have the same depth as the joists.

For the End Span

Tabulated Capacity 1002 plf

Top Bars # 4 at 10 in

Bottom Bars 2 # 7

Stirrups Single leg stirrups, # 3 spaced at 11 in for 123 in

For the Interior Span

Tabulated Capacity 1774 plf

Top Bars # 5 at 11 in

Bottom Bars 2 # 7

Stirrups Single leg stirrups, # 3 spaced at 11 in for 125 in

Concrete Quantity = 497 plf = 497/ (72”/12”) = 83 psf

Deflection:

CRSI: the computation of deflection is not required above the horizontal line (thickness

ln/18.5 for end spans, ln/21 for interior spans)


East Lansing, MI

2005 Senior Thesis

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Figure 7


East Lansing, MI

2005 Senior Thesis

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Flat Slab with Drop Panel Design Summary (US Standard)

Flat Slab with Drop Panels (US Standards)

Item Value Comment

Slab thickness 12.5” > Minimum

Drop panel thickness 3.5 > ¼ slab thickness

Drop panel size 10 ft2

Allowable shear stress 252.96 psi

Maximum shear 245.52 psi << Allowable

Maximum joint moment 945’ kip

Maximum joint shear 169 psi

Maximum deflection 0.266 in << Allowable

Figure 8


East Lansing, MI

2005 Senior Thesis

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Figure 9 – E-W Reinforcement for Flat Slab (US Standards)


East Lansing, MI

2005 Senior Thesis

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Figure 10 – N-S Reinforcement for Flat Slab (US Standards)


East Lansing, MI

2005 Senior Thesis

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Two-way Slab with Drop Panels (British Standards)

Two-way Slab with Drop Panels (British Standards)

Item Value Comment

Slab thickness 13.0” > Minimum

Drop panel thickness 3.5” > ¼ slab thickness







Figure 11


East Lansing, MI

2005 Senior Thesis

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Figure 12 – E-W Reinforcement for Flat Slab (British Standards)


East Lansing, MI

2005 Senior Thesis

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Figure 13 – N-S Reinforcement for Flat Slab (British Standards)


East Lansing, MI

2005 Senior Thesis

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Two-way Slab with Beams (British Standards)

Two-way Slab with Beams (Oman)

Item Value Comment

Slab thickness 10.5”

Drop panel thickness 3.5” > ¼ slab thickness







Figure 14


East Lansing, MI

2005 Senior Thesis

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Figure 15


East Lansing, MI

2005 Senior Thesis

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Figure 16 - Two-way Slab with Beams Reinforcement (E-W) (British Standards)


East Lansing, MI

2005 Senior Thesis

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Figure 17- N-S Two-way with Beams Reinforcement (British Standards)

structural design occupancy or use uniform (psf) concentrated (lbs) · 2005-05-12 · occupancy or...

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