cast in place and mechanical - american concrete institute

Bogota ACI Seminar August 13, 2014

Meinheit Anchorage to Concrete Presentation ‐ Part 1 1

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Cast‐in‐Place and Mechanical Anchors

ACI Seminar ‐ Bogota August 13, 2014

Review ACI history of anchoring to concrete Review failure modes for cast‐in‐place and expansion anchors Review basic design models Review relationship between ACI 318 and anchor qualification requirements

2

Learning Objectives



3

Definitions

Embedment

Attachment Anchor

Cast‐in‐place anchors Mechanical expansion anchors Bonded anchors

Anchor Types

4



Background

Page 5

Cast‐in‐Place Anchors

hef

hef

hef

Headed bolts Welded headed studs

J and L bolts

6



Mechanical expansion anchors Torque‐controlled Displacement‐controlled Undercut

7

Post ‐ Installed Expansion

8


Torque-Controlled Expansion Anchor

Heavy Duty Wedge Fastener Sleeve FastenerSleeve Fastener



9


Displacement-Controlled Expansion Anchor

Drop-In Fastener Self-Drilling Fastener Stud Fastener


Undercut Anchor

Pre-Drilled Undercut Cone Anchor Sleeve Creates lateral and bearing forces on concrete, concreteloaded in bearing not friction

10



2002 ACI 318 adopts provisions for anchorage design Provisions based on CCD method

– Cast‐in‐place anchor provisions– Mechanical expansion provisions

2011 ACI 318 includes provisions for adhesive anchors 2018 or 2020 will include concrete screws and grouted anchors and other updates on several design issues

Recent History and Near Future

11

Loading types Direct tension Direct shear Interaction of tension and shear Eccentric shear Seismic

Key: Understand potential failure modes

Fundamentals of Anchorage Design

12



13

Code Design Methodology

Load

Resistance

Load and Resistance

Pro

bab

ility

Limit probability

of failure

ACI 318 Strength Requirements

Nua ≤ NnVua ≤ Vn

Lowest Nn and Vn from applicable failure modes Resistance based on 5 % fractile of basic individual anchor strength 90% confidence that 95% of actual strengths will exceed nominal strength

14



Lower‐Bound Design Approach

5 % Fractile

Average (Mean) Strength Statistical parameters

Average (mean)

Standard deviation

Coefficient of variation

Number of samples

Test Capacity

Fre

qu

ency

15

ACI Code ProvisionsDesign for Tension, Shear, or Combinations of Tenson and Shear

Page 16



Tension Behavior – Failure Modes

Steel strength Concrete breakout strength Concrete side‐face blowout strength Pullout / pull‐through strength

Lowest value controls design

Concrete splitting strength

17

Tension ‐ Steel Failure

Ultimate tensile strength of steel material Effective cross‐sectional area

Nsa = Ase ( futa )

Nsa = Ase futa

futa < 1.9 fyfuta < 860 MPa

18



The strength corresponding to a volume of concrete surrounding the anchor or group of anchors separating from the member.

Concrete Breakout Strength

19

Tension – Concrete Breakout

20



Spacing and Edges

Spacing > 3hef

Edge distance >1.5 hef

Single anchor not near an edge

Single anchor near an edge

21

Edge effects Group effects Eccentricity Cracked vs. uncracked concrete Supplementary and/or anchor reinforcement intersecting potential concrete failure prism

Factors Affecting Tension Strength

22



Single Anchor Breakout Capacity

5% fractile capacity ‐ tension Cracked concrete

–Cast‐in‐place anchorsNb = 10 √fc’ (hef)

1.5

–Post‐installed anchorsNb = 7 √fc’ (hef)

1.5

These are the ACI 318 Code design equations for cracked concrete

23

24

User Friendly Breakout Model ‐Tension

35 hef

Plan View

ANco = 9 hef2

Single Anchor

Elevation

1.5hef 1.5hef1.5hef

1.5hef

1.5hef 1.5hef

~ 35o



User Friendly Anchor Group Breakout Model ‐Tension

ca1 s1 1.5hef

1.5hef

ca2

s2

NcoNc n AA

efa1 h5.1c

efa2 h5.1c

Multiple Anchor Group ‐ Near Two Edges

Free edge

Free edge

ANc = (ca1 + s1+ 1.5hef) (ca2 + s2+ 1.5hef)

Corner 25

26

Group Concrete Breakout Strength

Anchors in Tension

Ncbg = (ANc / ANco) ed,N

ec,N

c,N

cp,N

Nb



T1 T2 T3

e’N Resultant TensionLoad (T1 + T2 +T3 )

Centroid of Anchors Loaded in Tension

Nn

Eccentricity Effect –ec,N

27

Edge Effect – ed,N

hef

ca1

28



Cracking Effect – c,N

For Uncracked Concrete (ft < fr at Service Load) cast‐in anchors: c,N = 1.25 post‐installed anchors: c,N = 1.40

For cracked concrete: c,N = 1.00

29

30

Cracking Influence

Headed Studs

Load–displacement curves for uncracked and cracked concrete



Cracking Influence

Drop-in Anchors

Load–displacement curves of fully and partially expanded anchors in uncracked and cracked concrete

31

32

Cracking Influence

Sleeve anchors Load-displacemnt curves for designed to work in uncrackedconcrete but anchored in a line crack

Nn



Cracking Influence

0.7

Expansion anchors

Ratio is of concrete breakout loads

(Ncr [line cracks] /Nuncr)

33

Cracking Influence

Undercut and Headed Fasteners

Ratio is of concrete breakout loads (Ncr [line cracks] / N uncr)

34



Side‐Face Blowout

35

Side‐Face Blowout ‐Tension

Nn

'cbsb fAca113N

Single Headed Fastener with Deep Embedment, Close to Edge (ca1 ≤ 0.4 hef)

hef

ca1

So

36



Pullout / Pull‐through Failure

37

L-bolt straightenedout

Pullout/Pull‐through

For post‐installed expansion and undercut anchors Pullout/pull‐through strength (Np ) cannot be calculated using generic formulas

Np must be based on results of tests performed and evaluated per ACI 355.2

38



Headed Stud/BoltNp = 8 fc’ Abrg

J‐Bolt or L‐BoltNp = 0.9fc’ehda

where 3da eh 4.5da

Pullout Strength

Npn

39

Phi Factors ‐Tension

Steel failures Ductile steel = 0.75 Brittle steel = 0.65

Concrete breakout and adhesive bond failures Condition A Condition B

Category 1 0.75 0.65



Condition A – Supplemental steel Condition B – Plain concrete

40



Steel strength Concrete breakout strength Concrete pryout strength Concrete splitting strength

Lowest value controls design

Shear Behavior – Failure Modes

41

Welded headed stud anchors

Steel Failure ‐ Shear

42



Post‐installed sleeve anchor

Steel Failure ‐ Steel

43

Shear – Steel Strength

Vn

Vn = n Ase ()(futa)

44



Ultimate tensile strength of steel material Effective cross‐sectional area

Shear ‐ Steel Strength

Cast-in-place welded headed studsVsa = n Ase futa

Cast-in-place headed bolts, hooked bolts, post-installed anchorsVsa = n Ase (0.6 futa)

45

Similar to tension breakout Cracked volume about ½ of tension breakout

Occurs near free edges Shear toward front edge Shear toward side edge

Capacity dictated by critical fastener Welded headed stud attachment Bolted attachment

Shear – Concrete Breakout

46



Concrete Breakout ‐ Shear

47

5% fractile capacity ‐ shear

Cracked concrete

Vb = 0.6 a (e /da)0.2 √da √fc’ (ca1)

1.5

e = hef for anchors with uniform stiffness over hef

e 8da

e = 2da for torque‐controlled expansion anchors with a distance sleeve separated from expansion sleeve

Single Anchor Concrete BreakoutShear

Expansion sleeve

Distance sleeve

48



Single Anchor Concrete Breakout (Shear)

Single anchor in shear in cracked concrete

Vb = 3.7 a (fc’)0.5 (ca1)

1.5

Use the smaller of the two equations

4949

Edge effects Group effects Eccentricity Cracked vs. uncracked concrete Supplementary and/or anchor reinforcement intersecting potential concrete failure prism

Factors Affecting Strength

50



51

Front view

Vn

Edge of concrete

Plan view

Vn

hef

Side section

ca1

35o

1.5ca1 1.5ca1

1.5ca1

1.5ca1

1.5ca1AVco

AVco = 2 (1.5ca1) (1.5ca1)= 4.5(ca1)2

Projected Area for Single Anchor ‐Shear Breakout

51

52

AVcca1

1.5ca1 1.5ca1s1

Vn

ha

AVc = (2 x 1.5ca1 + s1)ha

If ha < 1.5ca1 and s1 < 3ca1

Projected Area for Shear Breakout ‐(Groups)

52



53

Projected Area for Shear Breakout ‐(Groups)

53

ca1ha

AVc

If ha < 1.5ca1

AVc = (2 x 1.5ca1) x ha Vn /2

Vn /2

1.5ca1 1.5ca1

54

Projected Area for Shear Breakout –(Groups)

54

ca1

AVc

1.5ca1 1.5ca1

Vn

ha

If ha < 1.5ca1

AVc = (2 x 1.5ca1)ha



55

Group Concrete Breakout Strength

Anchors in Shear

Vcgb = (AVo/AVco) ed,V

ec,V

c,V

h,VV

b

Edge Effect – ed,V

ca1

Vn

1.5ca1ca2

56



Eccentricity Effect –ec,V

Vn ev’s/2

s/2

Edge of Concrete

57

For Uncracked Concrete (ft< f

r) at Service

Load c,V

= 1.4 For Cracked Concrete

c,V= 1.0 No Reinf.* or < No. 4 Bar

c,V

= 1.2 With Reinf.* No. 4 Bar

c,V= 1.4 With Reinf.* No. 4 Bar (enclosed

within stirrups w / spacing 4 in.)

* Edge or Supplementary Reinforcement

Cracking Effect ‐c,V

58



Concrete Pryout ‐ Shear

59

Concrete Pryout ‐ Shear

Vcpg = kcpNcbg

where:

• kcp = 1.0 for hef < 2.5 in.

• kcp = 2.0 for hef > 2.5 in.

• Ncb Computed from Basic Tension Breakout

Vn

Applies to short, stocky anchors

60



Concrete Splitting Failure

NnNn

NnNn

61

62

Concrete Splitting Failure



Edge Distance: Preclude Splitting

Post‐Installed Anchors

Without Product‐Specific 355.2 Information:‐ undercut anchors ≥ 6da

‐ torque‐controlled anchors ≥ 8da

‐ displacement‐controlled anchors ≥ 10da

Cast‐in‐place Headed Anchors Untorqued: ≥ cover per Section 7.7 Torqued: ≥ 6da

63

Anchor Spacing: Preclude Splitting

Center‐to‐Center

Untorqued Cast‐in ≥ 4da

Torqued Cast‐in ≥ 6da

Post‐Installed ≥ 6da

64



Tension ‐ Shear Interaction

Nu

Nn

0.2Nn

0.2Vn VnVu

VV 3

0N

u 31

N5

n

u

5

n

.

2.1VV

NN

n

u

n

u

Simplification

65

ACI 355.2Qualification of Post‐Installed Mechanical Anchors in Concrete

66



Four types of tests: Identification tests Reference tests Reliability tests Service condition tests

ACI 355.2 Standard

67

Establish baseline performance of anchors for comparison with Reliability and Service‐Condition tests Establish primary characteristic anchor data

ACI 355.2 Reference Tests

68



Verify anchor capability for safe and effective behavior under normal and adverse conditions: During installation In service

Test conditions vary by anchor type and installation method

ACI 355.2 Reliability Tests

69

Determine performance under service conditions Minimum edge distance Minimum spacing distance Seismic Shear

ACI 355.2 Service Condition Tests

70



Cracked Concrete Testing

71

Independent Testing and Evaluation Agency Evaluates test results Issues a report classifying the anchor for use with ACI 318 Appendix D

ACI 355.2 Evaluation Report

72



Evaluation Report Data

7373

Questions and Answers

74

cast in place and mechanical - american concrete institute

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