ICH Anchorage to Concrete Seminar Santiago, Chile 19 – 20 Marzo 2015 March 2015 1 Buenos días! 2 www.sgh.com Anchorage to Concrete ACI 318-11 Appendix D ACI 318-14 Chapter 17 Neal S. Anderson, P.E., S.E. Staff Consultant Simpson Gumpertz & Heger, Chicago, Illinois [email protected]Member ACI 318 – Structural Concrete Bldg. Code Chair 318B – Anchorage & Reinforcement Seminar Materials Seminar slides handout Other good reference material • ACI 318-11, Chapter 2 and Appendix D • ACI 355.2-07 Qualification of Post-installed Mechanical Anchors in Concrete and Commentary • ACI 355.4-11, qualification of Post-installed Adhesive Anchors in Concrete and Commentary • ACI SP-17, ACI Design Handbook, Vol. 2 • SP-283, Understanding Adhesive Anchors: Behavior, Materials, Installation, Design • Code justification technical references 4 Seminar Handout 5 6
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ICH Anchorage to Concrete Seminar Santiago, Chile
19 – 20 Marzo 2015
March 2015 1
Buenos días!2
www.sgh.com
Anchorage to ConcreteACI 318-11 Appendix DACI 318-14 Chapter 17
Powder actuated - installed by shooting anchor into concrete
Expanding lead shield
Bonded Anchors
Adhesive anchors Grouted anchors Of the two bonded anchor types, ACI 318-11
currently provides design rules for only Adhesive Anchors
So, what is the difference?
28
Grouted Anchors Hole diameter > 1.5 x bar diameter
• Cementitious or polymer binders with filler• Generally vertical installations (although
some firms like AMBEX have developed horizontal)
• Typically headed anchor rods or reinforcing bars used
29
Zamora, N. A., Cook, R. A., Konz, R., and Consolazio, G. R., Behavior and Design of Single, Headed and Unheaded, Grouted Anchors, ACI Structural Journal, American Concrete Institute, V. 100, No. 2, March-April 2003, pp. 222-230.
Cook, R. A., Burtz, J. L., Design Guidelines and Specifications for Engineered Grouts used in Anchorages and Pile Splice ApplicationsReport No. BC 354 RPWO #48 Florida Department of Transportation , Tallahassee, FL, August 2003, 119 pp.
Adhesive Anchors Hole diameter < 1.5 x bar diameter
• Frequently used • Covered by ACI 318-11• Typically polymer binders but cementitious
fillers mixed with polymer available
30
ICH Anchorage to Concrete Seminar Santiago, Chile
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Adhesive Anchor Materials
31
Adhesive Anchor Materials Epoxy Acrylates
• Resins – Part A; Curing agent – Part B• Almost no shrinkage during curing
Polyesters• Short shelf life; Degrade with exposure to
sunlight; can polymerize without catalysis Vinyl esters
• Faster curing than epoxies slower than polyesters Hybrid systems
• Cement improves stiffness at high temperature• Negligible material shrinkage
32
33
Relative Bond Stress ComparisonAdhesive and Grouted
1800
2342
1659
2259
1780
2850
2663
447
793
1631
2227
1450
2314
1627
2480
2013
2564
334
1656
2104
3055
3040
2306
2579
2872
2586
2901
2946
1063
0
1000
2000
3000
4000
A B C D E F G H I J K L M N O P Q R S T 1 2 3 4 5 6 7 8 9
Product
Ave
rag
e U
nif
orm
Bo
nd
Str
es
s, [
ps
i]
Adhesive uncr mean = 1850 psi [12.7 MPa]
Grouted uncr mean = 2590 psi [17.9 MPa]
Adhesive Grouted
BACKGROUNDHistory of code anchorage design
34
35
History – Early Concrete Breakout Model – Circa 1961
Courtois ACI SP - 22
Concrete Breakout Models
36
45o about 35o
45o cone model 35o cone modelConcrete Capacity Design Model
Concretefracturesurface
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37
Differences Between Models
CCD
45o Failure Angle 35 o Failure Angle
45o Cone
Nc = kc,45 fc’ hef2 Nc = kc,CCD fc’ hef
1.5
38
45o Cone Breakout Prediction
0
1
2
3
4
5
0 50 100 150 200
Effective Embedment , mm
Obs
erve
d /
Pre
dict
ed
Mean = 1.642COV = 0.338
45o cone method
Single anchor behavior
39
CCD Breakout Prediction
0
1
2
3
4
5
0 50 100 150 200
Effective Embedment, mm
Obs
erve
d /
Pre
dict
ed
Mean = 0.994COV = 0.196
CCD method
Single anchor behavior
40
Failure Angle
0
10
20
30
40
50
0 100 200 300 400 500Embedment length ( mm )
Fai
lure
ang
le (
degr
ees)
n = 11n = 9 n = 6
hef
hef
Failure angle
45o cone
41
History of ACI Anchorage Design ACI 318 Appendix D
Prior to 2002• Model codes (UBC), ACI 349 (Nuclear Structures) • Industry guidelines – PCI Design Handbook• Considered only cast-in-place anchors in uncracked
concrete• Only steel failure and concrete breakout considered
breakout based on 45 – degree cone model
2002 : ACI 318-02 Appendix D published• Cast – in and post – installed mechanical anchors• CCD Method (35 - degree pyramid model)• Cracked concrete
History of ACI 318 Appendix D
2011: ACI 318-11 Appendix D • Includes bonded anchors but only adhesive
D.5.2.1 - Concrete Breakout Strength of Anchor Group (Tension)
Accounts for post - installed anchor (splitting)
Accounts for cracking
Accounts for edge effects
Accounts for eccentricity
Accounts for projected area of failure surface Basic single anchor strength
Applies to only anchors in tension
Ncbg = (ANc /ANco ) ec,N ed,N c,N cp,N Nb (D-4)
124
D.5.2.2 - Basic Single Anchor Breakout Strength
Single anchor in tension in cracked concrete
Nb = kc a (fc’)1/2 (hef )3/2 (D – 6)
kc = 10 for cast - in anchors
kc = 7 for post - installed anchors
a = Lightweight concrete modification factor
Note: an adhesive anchor should be considered like a post-installed anchor even though there are no wedging forces developed at embedded end for concrete breakout
125
User Friendly CCD Design Model for Concrete Breakout – Projected Area ANco
hef
1.5hef
1.5hef
1.5hef
Plan ViewElevation
ANco = 9hef
1.5hef
Nn
1.5hef 1.5hef
2
350
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Concrete Breakout with Groups and Edges - Projected Area ANc
ca1 s1 1.5hef
1.5hef
Ca2
s2
ef1 h0.3s
efa2 h5.1c ef2 h0.3s
efa1 h5.1c
Limit
127
Corner
ANc ≤ nANco
128
D.5.2.6 – No Cracking Influence
Uncracked Concrete (ft < fr at service load)• Cast-in anchors: c,N = 1.25
• Post-installed anchors: c,N = 1.40 where kc = 7 in Eq. (D - 6)
• When product evaluation testing is based on ACI 355.2 or 355.4 and the anchors are used in cracked and uncracked concrete, then : kc and c,N are determined from the evaluation report
• When product evaluation testing is used to determine kc,uncr then: c,N = 1.00
D.5.5.1- Bond Strength of Adhesive Anchor Adhesive Group
Nag = (ANa /ANao) ec,Na ed,Na cp,Na Nba (D-19)
Tension failure = Bond failure < Concrete failure
129
Accounts for splitting
Accounts for edge effects
Accounts for eccentricity
Accounts for projected area of influence areaBasic single anchor bond strength
D.5.5.2. - Basic Bond Strength
Single anchor in cracked concrete
Nba = a cr da hef (D-22)
cr = 5% fractile result in cracked concrete from ACI 355.4
a = Lightweight concrete modification factor for adhesive anchors
a,lightweight = 0.6 normal [0.6 factor not applicable for normal-weight concrete]
130
h ef-
incr
easi
ng
s -
cons
tant
h ef-
cons
tant
s
–de
crea
sing
da
hef
hef
da
da
hef
s
da
s
da
s
da
Adhesive Anchor Group Failure
131
s
s
s
Influence Area for Single Adhesive Anchor
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Critical Spacing and Edge Distance
Cast-in-place and post-installed mechanical anchors• ACI 318-11
Use hef in code equations containing hef equal to the larger of :
• ca,max / 1.5, and• (1 / 3) maximum spacing between anchors
where ca,max = maximum distance from anchor to edge
141
Determine Fictitious Embedment Depth, hef'
Fictitiously move the actual concrete breakout surface toward the free surface of concrete until it first contacts the free surface
Consider a square concrete pier :
hef
hef'
Actual concrete breakout surface
Fictitious concrete breakout surface,by § D.5.2.3
142
Reason for Fictitious Embedment Depth, hef’
In the equation for calculating ANco, hef appears in the denominators of the single and group design equations for concrete breakout strength, and the denominator increases as a function of hef
2
In the basic single anchor concrete breakout strength, hef
appears in the numerators of the single and group equations and the numerator increases as a function of hef
1.5
If hef' is not determined in accordance with § D.5.2.3, the result is an overly conservative prediction for concrete breakout strength
143
AssumedFailure Surface
4 in.
Expected Failure Surface
Nn
9 in.
6 in.
5.5 in.
5 in.
Point A
Expected Failure Surface Assumed Failure Surface
5.5 in.h’
ef
h’ef
Fictitious h’ef Larger of
ca,max/1.5 = 6/1.5 = 4 in.
s/3 = 9/3 = 3 in.
Fictitious Embedment, hef’
144
D.5.2.7 – Post-installed Anchors in Uncracked Concrete Without
For post - installed expansion and undercut anchors , Np cannot be calculated using generic formulas Np must be based on results of tests
performed and evaluated per ACI 355.2
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D.5.3.6 – Pullout Strength Cracking Modifiers
Uncracked Concrete c,p = 1.4• (ft < fr at Service Load)
Cracked Concrete c,p = 1.0
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D.1 - Definitions
Side - Face Blowout Strength
The strength of fasteners with deeper embedment but thinner side cover corresponding to concrete spalling on the side face around the embedded head while no major breakout occurs at the top concrete surface
Applies to cast-in-place anchors only
Side–face Blowout Failure
Local side-face blowout caused by bearing pressure (stress) of head on concrete (should be ~8fc’) producing lateral force
Nsb = 1/ Nb
• Lateral force (Nsb) a function of the tension force on anchor
• depends on the bearing pressure beneath the head
153
D.5.4.1 – Side-face Blowout
Single headed anchor with deep embedment , close to edge ( ca1 < 0.4 hef )
Nsb = 13 (ca1) (Ab)0.5 (fc’)0.5 (D-16)
If perpendicular edge distance ca2 < 3 ca1 , modify Nsb by :
( 1 + ca2 / ca1 ) / 4
where 1.0 ca2 / ca1 3.0154
D.5.4.2 – Side-face Blowout
For multiple headed anchors with deep embedment , close to edge (hef > 2.5 ca1) or (ca1 < 0.4 hef) and s < 6 ca1
Nsbg = [1 +s / (6ca1)] Nsb (D-17)
where
s = distance between outer anchors along edge
Nsb is from Eq. (D - 16) without modification for perpendicular edge distance (ca2)
155
D.8.6 – Critical Edge Distance, cac
Post-installed Anchors
Without tension test data from ACI 355.2 or ACI 355.4:
Note: No special code clauses for the shear design of adhesive anchors
161
D.6.1 – Steel Failure ( Shear )
Concretecrushing
Void
Shear force
Vn
Steel Failure - Shear
Void behind the anchor
163
D.6.1.2 – Steel Strength (Shear)
(b) Cast-in headed and hooked anchor bolts, and post-installed anchors (including adhesive anchors) without sleeves extending through shear plane
Vsa = (0.6 )Ase,V futa (D - 29)
where futa 1.9 fya
890 MPa- With built-up grout pads, use 0.8 Vsa
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164
D.6.2 – Concrete Breakout (Shear)
Edge distance
Vn
Concrete Breakout (Shear)
Concrete Breakout (Shear)
167
D.6.2.2 – Basic Single Anchor Concrete Breakout (Shear)
Single anchor in shear in cracked concrete
e = hef for anchors with uniform stiffness over hef
e 8 da
e = 2 da for torque - controlled expansion anchors with a distance sleeve separated from expansion sleeve
Expansion sleeve
Distance sleeve
Vb = 0.6a (e / da)0.2 da
0.5 fc’ 0.5 (ca1)
1.5 (D -33)
D.6.2.2 – Basic Single Anchor Concrete Breakout (Shear)
Single anchor in shear in cracked concrete
Vb = 3.7 a (fc’)0.5 (ca1)
1.5 (D - 34)
Use the smaller of D-33 or D-34
168
Shear Breakout Test Database(no limit on anchor diameter)
169
Data point with new equation
Fit of new ACI 318-11provisions
Data point with old equation Fit of old provisions
Diameter da (in)
Vte
st/
Vp
red
icte
d
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170
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
(D-32)
Projected Area for Single-Anchor Shear Breakout
171
D.6.2.1(b) – Concrete Breakout Strength of Anchor Group (Shear)
Vcbg = (AVc / AVco) ec,V ed,V c,V h,V Vb (D-31)
Accounts for projected area of failure surface
Accounts for eccentricity
Accounts for edge effects
Accounts for cracking
Accounts for thickness
Basic single anchor strength
172
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)
173
ca1ha
AVc
If ha < 1.5ca1
AVc = (2 x 1.5ca1) x ha
Vn /2
Vn /2
1.5ca1 1.5ca1
Projected Area for Shear Breakout (Groups)
174
ca1
AVc
1.5ca1 1.5ca1
Vn
ha
If ha < 1.5ca1
AVc = (2 x 1.5ca1)ha
Projected Area for Shear Breakout (Groups)
175
D.6.2.4 – Anchors Close to 3 or 4 Edges
Where 3 or more edge distances 1.5 ca1 Effective ca1 used in Eq. (D - 30) through (D - 39) must not exceed the largest of :• ca2 / 1.5• ha / 1.5• ( 1 / 3 ) maximum spacing between anchors
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176
D.6.2.4 – Anchors Close to 3 or 4 Edges
c’a1
9 in. 8 in.
Vn
Point A
5 in. 7 in.
Assumed Failure Surface for Limiting ca1
ca1 =12 in.
Expected Failure Surface
Shear Parallel to Free Edge
Concrete breakout
ca2 = 4da
178
D.6.2.1(c)-(d) – Shear Parallel to Edge
Vn perp
2Vn perp
Actual Compute
Compute shear strength perpendicular to edge, Vn perp
Based on testing, shear strength parallel to edge = 2 Vn perp
For shear force parallel to edge (ed,V = 1 )• Vcb = 2 [ Vcb per Eq. (D-30)]• Vcbg = 2 [ Vcbg per Eq. (D-31)]
At corner, use smaller of :• Shear strength perpendicular to edge• Shear strength parallel to edge
D.6.2.5 – Eccentricity Effect
180
Edge of concrete
ca1
D.6.2.5 – Eccentricity Effect
For anchor groups
consider only anchors resisting shear in direction of load, that is, shear perpendicular or shear parallel to free edge
181
ec,V = 1 / (1+ 2ev’ / 3ca1) (D-36)
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182
D.6.2.6 Side-Edge Effect
ca1
Vn
1.5ca1ca2
D.6.2.6 – Side-edge Effect
If ca2 1.5 ca1
ed,V = 1.0 ( D - 37 )
If ca2 < 1.5 ca1
183
( D - 38 )ed,V = 0.7 + 0.3 ( ca2 / 1.5 ca1)
184
For uncracked concrete (ft < fr ) at service load c,V = 1.4
For Cracked Concrete
• c,V = 1.0 No reinforcement * or < No. 12 bar
• c,V = 1.2 With reinforcement * No. 12 bar
• c,V = 1.4 With reinforcement * No. 12 bar
( enclosed within stirrups w / spacing 100 mm)
* Edge or Supplementary Reinforcement
D.6.2.7 – No Cracking Effect
185
D.6.2.7 – No Cracking Effect
c,V = 1.0
c,V = 1.2
c,V = 1.4
D.6.2.8 – Correction for Thickness
Testing fact – concrete breakout strength in shear not linear with member thickness as breakout model would predict and can provide higher capacities
If ha < 1.5 ca1 , that is, when the breakout projects to the bottom of the slab, then an addition correction is needed
h,V = ( 1.5 ca1 / ha ) 0.5 (D – 39)
186 187
D.6.3 – Concrete Pryout
Vn
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Concrete Pryout - Shear
189
D.1 - Definitions
Concrete Pryout Strength
The strength corresponding to formation of a concrete spall behind a short , stiff anchor with an embedded base that is displaced in the direction opposite to the applied shear force
190
D.6.3 – Concrete Pryout
Single Anchor Vcp = kcp Ncp (D - 40) Group of Anchors Vcpg = kcp Ncpg (D - 41)
where:
• kcp = 1.0 for hef < 64 mm.
• kcp = 2.0 for hef 64 mm
• Ncp = Na computed from Eq. (D - 18)
• Ncpg smaller of Nag [Eq. D - 19] and Ncbg [Eq. D - 4]
Concrete breakout and adhesive bond failure• Shear loads, Condition A = 0.75• Shear loads, Condition B = 0.70
191
193
D.7 - Tension / Shear Interaction
Nu
Nn
0.2 Nn
0.2 Vn Vn
Vu
[Nua /Nn ] 5/3 + [Vua /Vn ]
5/3 = 1.0
[Nua /Nn ] + [Vua /Vn ] = 1.2
(D – 42)
D.7 – Tension / Shear Interaction The values used in the denominator of the
interaction equation are the required strengths determined in § D.4.1.1 or § D.3.3.3 (seismic)
194
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D.7 – Tension / Shear Interaction
What happens if anchor reinforcement is used?
This means that if you design anchor reinforcement for either tension or shear, or both, the interaction equation does not have to be checked
195
SPLITTING FAILURES
196
197
Concrete Splitting Failure – Prescriptive
NnNn
NnNn
Design Method for Splitting Failure Mode of Adhesive Anchors, ACI SP-283 Paper No. 6 by Jorg Asmus
Concrete Splitting Failure
199
D.8 – Preclude Splitting Failure
At design stage, specific products may not be known
In absence of supplementary reinforcement for crack control, Section D.8 sets minimum requirements for cover, spacings, member thickness
Lesser values are permitted per ACI 355.2 and ACI 355.4
200
D.8.3 – Edge Distance
Post - Installed Anchors
Edge distance must exceed the largest of :
Cover per Section 7.7 Twice the maximum aggregate size Minimum edge distance for product per
ACI 355.2 and ACI 355.4
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201
D.8.3 – Minimum Edge Distance
Post-installed Anchors
Without product – specific information from ACI 355.2 or ACI 355.4:
- Adhesive anchors ≥ 6da
- Undercut anchors ≥ 6da
- Torque – controlled anchors ≥ 8 da
- Displacement – controlled anchors ≥ 10 da
D.8.5 – Minimum Thickness
Expansion & Undercut Anchors
Without product - specific information from ACI 355.2 :
• hef must not exceed the larger of
2 / 3 member thickness
member thickness minus 4 in.
202
203
D.8.6 – Critical Edge Distance, cac
Post-installed Anchors
Without tension test data from ACI 355.2 and ACI 355.4 and without supplementary reinforcement to control splitting :
- Adhesive anchors ≥ 2 hef
- Undercut anchors ≥ 2.5 hef
- Torque-controlled anchors ≥ 4 hef
- Displacement-controlled anchors ≥ 4 hef
204
D.9 – Anchor Installation and Inspection
§ D.9.1• Anchors to be installed by qualified personnel• Installation in accordance with Manufacturer’s
Printed Installation Instructions (MPII) § D.9.2
• Extensive installation, inspection, and proof load requirements
SEISMIC CONSIDERATIONS
Chilean Earthquake February 27, 2010 - 8.8 magnitude
205
D.3.3 - Seismic Design Requirements
Seismic load effects covered • Applicable to Seismic Design Categories
(SDC) C, D, E, and F § D.3.3.2 – Anchors in plastic hinge zones
excluded § D.3.3.3 - Post-Installed Anchors shall be
qualified for earthquake loading per ACI 355.2 or ACI 355.4 Simulated Seismic Tests
206
ICH Anchorage to Concrete Seminar Santiago, Chile
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Simulated Seismic Tests
Tension Shear
207
50%75%
Neq = 0.5 No,mean Veq = 0.5 Vo,mean
50%75%
208
D.3.3 – Seismic Design Requirements (Tension)
§ D.3.3.4.2 – Anchors carrying tension in structures assigned to SDC C, D, E, or F• If
The tensile component of the strength-level earthquake force is equal to or less than 20% of the total factored anchor tensile force associated with same load combination
• Then
Design using the normal design procedure in § D.5 and § D.4.1.1
209
D.3.3 – Seismic Design Requirements (Tension)
D.3.3.4.2 - Anchors carrying tension in structures assigned to SDC C, D, E, or F• If
The tensile component of the strength-level earthquake force is exceeds 20% of the total factored anchor tensile force associated with same load combination
• Then
Design using rules in § D.3.3.4.3 and anchor design tensile strength is determined by § D.3.3.4.4
210
D.3.3 – Seismic Design Requirements (Tension)
§ D.3.3.4.3 - Anchors carrying tension and their attachments shall satisfy one of the options (a) through (d)
(a) Ensure anchor ductility, that is, use 1.2 times the nominal steel strength, provide a stretch length
(b) Anchor designed for tension force associated with expected strength of the metal attachment
(i) Anchor design by § D.3.3.4.4
(c) Design for maximum tension which can be transmitted by a non-yielding attachment
(i) Anchor design by § D.3.3.4.4
(d) Design for maximum tension obtained from load combination with E, but with E increased by o
(i) Anchor design by § D.3.3.4.4
(ii) Recommended o about 2.5
211
D.1 - Stretch Length
212
D.3.3 – Seismic Design Requirements (Tension)
§ D.3.3.4.4 - Anchor Design Tensile Strength
a) 0.75Ncb or 0.75Ncbg (need not be calculated if anchor reinforcement is used)
b) 0.75Npn
c) Nsa for single anchor or most highly stressed
d) 0.75Nsb or 0.75Nsbg
e) 0.75Na or 0.75Nag
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D.3.3 – Seismic Design Requirements (Shear)
§ D.3.3.5.1 – Anchors carrying shear in structures assigned to SDC C, D, E, or F• If
The shear component of the strength-level earthquake force is equal to or less than 20% of the total factored anchor shear force associated with same load combination
• Then
Design by § D.6 and § D.4.1.1
214
D.3.3 – Seismic Design Requirements (Shear)
§ D.3.3.5.2 - Anchors carrying shear in structures assigned to SDC C, D, E, or F• If
The shear component of the strength-level earthquake force is exceeds 20% of the total factored anchor shear force associated with same load combination
• Then
Design by § D.3.3.5.3 and anchor design shear strength is determined by § D.6
D.3.3 – Seismic Design Requirements (Shear)
§ D.3.3.5.3 – Anchors carrying shear and their attachments shall be design using one of the options (a) through (c)
(a) Ensure ductile yielding mechanism in attachment
(b) Design for the maximum shear that can be transmitted by non-yielding attachment
(c) Design for maximum shear obtained from load combination with E, but with E increased by o
(i) Anchor design by § D.4.1.1
(ii) Recommended o about 2.5
215 216
D.3.3.7 – Seismic Anchor Reinforcement
Anchors in structures assigned to SDC C, D, E, or F• Use deformed bar reinforcement
• ASTM A615 Grades 280 and 420 satisfying 21.1.5.2(a)(b) (Grades 520 and 550 not permitted)
• ASTM A706 Grade 420 (Grade 550 not permitted)
Tension
Shear
DESIGN FOR MOMENT (ECCENTRIC SHEAR)
217
Photograph courtesy of Hilti AG
218
Using ACI 318-11 Appendix D for Designs Involving Moment (Eccentric shear)
Effect of baseplate flexibility on:• Design tensile anchor forces in connections with
multiple rows of anchors
• Design moments in baseplates
Effect of friction on design shear forces in anchors
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Base Plate Flexibility Plane sections do not remain plane – beam
theory is not exactly correct, but close enough
For design purposes, bound the solution
• To size the anchors for tension, assume a flexible baseplate. This gives the smallest internal lever arm, and the largest design axial forces in the anchors
• To size the baseplate, assume a rigid baseplate. This gives the largest distance from the assumed location of the compression reaction to the critical point on the baseplate
220
Flexible Base Plate . . .
x = 0 (conservative for anchor tension)x = plate thickness (a reasonable assumption)x = Mp / C (reality for a flexible baseplate)
221
. . . Rigid Base Plate
This assumption is conservative for computing the design moment in the baseplate, because it places the compressive reaction at the tip of the baseplate
222
Effect of Friction on Design Shear Forces in Anchors
Regardless of baseplate flexibility, most shear resistance is provided by friction
ACI 318 - 11 conservatively neglects friction
If friction is neglected, assume that the shear is transferred by the anchors closest to the nearest free edge
If friction is assumed to exist, use = 0.4 and assume that the shear is transferred to the anchors closest to the compression resultant
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Multiple Rows of Anchors Load Distribution :
Loads in anchors are distributed according to stiffness (elastic design) or strength (plastic design)
Kinematics :Deformations of each anchor must be consistent with the deformations of the attachment
with distance from axis of rotation; capacity governed by critical anchor
Plastic approach: anchor forces are limited by anchor capacity; redistribution among anchors is possible if anchors are ductile; sufficient embedment is required to develop anchor capacity
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19 – 20 Marzo 2015
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ACI QUALIFICATION TESTING STANDARDS
ACI 355.2 :Qualification of Post-Installed Mechanical Anchors in Concrete and Commentary
ACI 355.4 :Qualification of Post-Installed Adhesive Anchors in Concrete and Commentary
226 227
Scope of ACI 355.2 and ACI 355.4 355.2 Post-installed mechanical anchors
Determine basic data required to predict the performance of anchors under service conditions• Verify full concrete capacity in a corner with
edges located 1.5 hef away• Establish minimum spacing and edge distances
to preclude splitting on during installation (torqueing) and tension loading
• Seismic tension• Establish shear capacity of anchor steel (may be
calculated)
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19 – 20 Marzo 2015
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Additional ACI 355.4 Service-Condition Tests
Verify anchor behavior under• Elevated temperature installation• Curing time at low temperatures • Resistance to alkalinity• Resistance to sulfur
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Influence of Temperature
245
ACI 355.2 and 355.4 Evaluation Report
Independent Testing and Evaluation Agency • Evaluates test results• Issues a report classifying the anchor for use
with ACI 318 Appendix D Bond Stress in the Evaluation Report is the
5% fractile including effects of all variables
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Evaluation Report Data
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INSTALLERCERTIFICATION
ACI 318-11 D.9.2
248
Courtesy of Hilti AG
Adhesive Anchor Installer Certification
A New ACI 318-11 Requirement
249
D9.2.2, D9.2.3, and D.9.2.4
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19 – 20 Marzo 2015
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How Did We Get Here (Part 1)?
Adhesive anchors • Versatile connection in the engineer’s toolbox• Installation to follow Manufacturer’s
instructions Design parameters now codified
• Structural design• Material performance
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How Did We Get Here (Part 2)?
2006 Boston experience revealed many issues . . . . • Manufacturer’s instructions vary• Structural design procedures had not been
formulated • Material performance consistency was somewhat
established in International Code Council-Engineering Service – Acceptance Criteria 58 (ICCC-ES AC58)
• Installation is not easy NTSB Report – misses real and primary
cause251
“use its building codes, forums, educational materials, and
publications to inform design and construction agencies of the potential
for gradual deformation in anchor adhesives under sustained tensile-
load applications”
NTSB Recommendation to ACI How Did We Get Here (Part 3)?
To get approval of adhesive anchors by ACI Committee 318, certification was imperative • Critical connections• Installation can be plagued with errors• On par with structural welding
Many factors are installer dependent – Certification necessary
ACI’s Response to NTSB
ACI 318-11 Building Code, addresses adhesive anchors
ACI has a standard for adhesive anchors (ACI 355.4) “Acceptance Criteria for Qualification of Post-Installed Adhesive Anchors in Concrete and Commentary”
Partnered with the Concrete Reinforcing Steel Institute (CRSI) to identify criteria for an Adhesive Anchor Installer (AAI) and develop a certification program
ICH Anchorage to Concrete Seminar Santiago, Chile
19 – 20 Marzo 2015
March 2015 43
Appendix D, Section D.9.2.2
D.9.2.2 — Installation of adhesive anchors horizontally or upwardly inclined to support sustained tension loads shall be performed by personnel certified by an applicable certification program. Certification shall include written and performance tests in accordance with the ACI / CRSI Adhesive Anchor Installer Certification program, or equivalent.
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Façade Attachment(sustained tension in downhand application)
257
MHinge or hard
welded connection
Appendix D, Section D.9.2.3
D.9.2.3 — The acceptability of certification other than the ACI / CRSI Adhesive Anchor Installer Certification shall be the responsibility of the licensed design professional.
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Summary
259
Ap
pen
dix
D -
Des
ign
Adhesive Anchor Installer Certification
Objective: Get classroom and practical training Show minimum level of competencyBe tested and certified by a trade association
And you ask, “Why do we need Certification?”
Actual hidden camera on a jobsite
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19 – 20 Marzo 2015
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Adhesive Systems
Nozzle mixing
• Zigzag type of nozzle tube
Capsule
• Insert in hole, break packaging, and mix
Bulk mixed
• Component A
• Component BNot included in program
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Quickly, Program Consists of: Training
• Classroom instruction
• Exposure to equipment and practice
75 question written examination• Closed book, 90 minutes
2 x allowable service load ~ 0.7 characteristic bond strength ~ 0.5 average ultimate bond strength
• Note that the allowable service load is used, not the calculated service load
80 percent of the rod steel yield strength
Obviously use whichever is smaller
Short-term loadingSilva, J. and Mattis, L. [2011], Special Inspection Guidelines for Post-installed Anchors, Concrete Anchor Manufacturers Association (CAMA), St. Charles, Missouri, June, 13 pp. (available from the CAMA website)