R. A. Cook ACI Atlanta 2007 Hot Topic 1 1 University of Florida University of Florida Department of Civil Engineering Department of Civil Engineering ANCHORAGE TO CONCRETE ANCHORAGE TO CONCRETE - SELECTION AND DESIGN SELECTION AND DESIGN Ronald A. Cook, Ph.D., P.E. Professor Department of Civil Engineering University of Florida 2 University of Florida University of Florida Department of Civil Engineering Department of Civil Engineering APPLICATIONS APPLICATIONS • Fasten an Attachment (Concrete, Steel, or Timber Element) to Concrete, e.g. – Precast element to precast element – Roof truss to tilt-up concrete wall – Steel column to concrete footing – Wood frame to concrete – Connections to concrete in general 3 University of Florida University of Florida Department of Civil Engineering Department of Civil Engineering General Types of Anchors General Types of Anchors Undercut Expansion Cast-in-Place Adhesive Grouted Covered by ACI 318-05 Bonded Mechanical Not Covered by ACI 318-05 Screw 4 University of Florida University of Florida Department of Civil Engineering Department of Civil Engineering Overview: Overview: • How today’s codes and standards work together for selection of anchors: – Design – Product Approval • Design and product approval considerations – Cast-in-Place – Post-Installed Mechanical – Bonded 5 University of Florida University of Florida Department of Civil Engineering Department of Civil Engineering What “Design” and “Product Approval” What “Design” and “Product Approval” Mean in Today’s Codes and Standards for Mean in Today’s Codes and Standards for Anchorage to Concrete Anchorage to Concrete • Design: – Based on Strength (LRFD) design concepts – No more “Allowable Load” Tables – Requires the expertise of a Professional Engineer • Product Approval – Must be based on criteria that are “in-sync” with the design provisions 6 University of Florida University of Florida Department of Civil Engineering Department of Civil Engineering How Today’s Codes and Standards Work How Today’s Codes and Standards Work for Selection of Anchors: for Selection of Anchors: Design and Product Approval Design and Product Approval • Cast-in-place anchors • Post-installed mechanical anchors • Screw anchors • Bonded anchors – Adhesive anchors – Grouted anchors
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R. A. Cook ACI Atlanta 2007 Hot Topic
1
1University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
ANCHORAGE TO CONCRETEANCHORAGE TO CONCRETE-- SELECTION AND DESIGNSELECTION AND DESIGN
Ronald A. Cook, Ph.D., P.E.ProfessorDepartment of Civil EngineeringUniversity of Florida
2University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
APPLICATIONSAPPLICATIONS• Fasten an Attachment (Concrete, Steel,
or Timber Element) to Concrete, e.g.– Precast element to precast element– Roof truss to tilt-up concrete wall– Steel column to concrete footing– Wood frame to concrete– Connections to concrete in general
3University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
General Types of AnchorsGeneral Types of Anchors
Undercut ExpansionCast-in-Place
Adhesive Grouted
Covered by ACI 318-05
BondedMechanical
Not Covered by ACI 318-05
Screw4University of FloridaUniversity of Florida
Department of Civil EngineeringDepartment of Civil Engineering
Overview:Overview:• How today’s codes and standards work
together for selection of anchors:– Design– Product Approval
• Design and product approval considerations– Cast-in-Place– Post-Installed Mechanical– Bonded
5University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
What “Design” and “Product Approval” What “Design” and “Product Approval” Mean in Today’s Codes and Standards for Mean in Today’s Codes and Standards for
Anchorage to ConcreteAnchorage to Concrete• Design:
– Based on Strength (LRFD) design concepts– No more “Allowable Load” Tables– Requires the expertise of a Professional
Engineer• Product Approval
– Must be based on criteria that are “in-sync” with the design provisions
6University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
How Today’s Codes and Standards Work How Today’s Codes and Standards Work for Selection of Anchors:for Selection of Anchors:
Design and Product ApprovalDesign and Product Approval
7University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
CastCast--inin--Place AnchorsPlace Anchors
hef = Effective Embedment Depth
hef
8University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Design of CastDesign of Cast--inin--Place AnchorsPlace Anchors
IBC 2006§1912
ACI 318-05§8.1.3
ACI 318-05Appendix D
9University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
IBCIBC––2006 Provisions2006 Provisions
10University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
ACI 318ACI 318--05 Provisions05 Provisions
• Appendices are generally not mandatory• ACI 318 Chapter 8 “Analysis and Design –
General Considerations” §8.1.3 makes Appendix D mandatory:
8.1.3 — Anchors within the scope of Appendix D, Anchoring to Concrete, installed in concrete to transfer loads between connected elements shall be designed using Appendix D.
11University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Product Approval for CastProduct Approval for Cast--inin--Place Place AnchorsAnchors
IBC 2006§1912
ACI 318-05§8.1.3
ACI 318-06Appendix D
§D.2.3
…
12University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Product Approval for CastProduct Approval for Cast--inin--Place Place Anchors Anchors –– ACI 318ACI 318--06 Appendix D06 Appendix D
Lot’s of text but basically any standard headed anchor or hooked anchor will meet these requirements
…
R. A. Cook ACI Atlanta 2007 Hot Topic
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13University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
CastCast--inin--Place Anchors:Place Anchors:Effects of CrackingEffects of Cracking
Headed AnchorsCurves in uncracked and cracked concrete
14University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
17University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Design of PostDesign of Post--Installed Installed Mechanical AnchorsMechanical Anchors
IBC 2006§1912
ACI 318-05§8.1.3
ACI 318-05Appendix D
18University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
IBCIBC––2006 Provisions2006 Provisions
R. A. Cook ACI Atlanta 2007 Hot Topic
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19University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Product Approval for PostProduct Approval for Post--Installed Mechanical AnchorsInstalled Mechanical Anchors
ACI 318-05§3.8.6
IBC 2006§1912
ACI 318-06Appendix D
§D.2.3
D.2.3 — Headed …. Post-installed anchors that meet the assessment requirements of ACI 355.2 are included. The suitability of the post-installed anchor for use in concrete shall have been demonstrated by the ACI 355.2 prequalification tests.
20University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
3.8.6 — “Qualification of Post-Installed Mechanical Anchors in Concrete (ACI 355.2-04)” is declared to be part of this code as if fully set forth herein, for the purpose cited in Appendix D.
21University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Product Approval for PostProduct Approval for Post--Installed Installed Mechanical Anchors:Mechanical Anchors:
ACI 318ACI 318--06 Appendix D06 Appendix DD.2.3 — … Post-installed anchors that meet the assessment requirements of ACI 355.2 are included. The suitability of the post-installed anchor for use in concrete shall have been demonstrated by the ACI 355.2 prequalification tests.
ACI 355.2-04
22University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Product Approval for PostProduct Approval for Post--Installed Mechanical Anchors:Installed Mechanical Anchors:
How this is currently implementedHow this is currently implemented
ICC ES AC193 ACI 355.2-04
ICC ESEvaluation
Report
23University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
“…having an evaluation report does not obligate the AHJ (Authority Having Jurisdiction) to approve the evaluated product. The report is simply technical evidence upon which the AHJ can approve the product if, on the job site, it is used within the report conditions. The approval decision lies with the AHJ.”
Ref.: “Code Approval”; The Basics, The Subtleties, and The Abuses www.icc-es.org
28University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Bonded AnchorsBonded Anchors-- Adhesive and Grouted Adhesive and Grouted (not covered by ACI 318(not covered by ACI 318--05)05)
AdhesiveHole diameter
≤ 1.5 anchor diameter
GroutedUnheaded Headed
Hole diameter > 1.5 times anchor diameter
29University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Design and Product Approval of Design and Product Approval of PostPost--Installed Adhesive AnchorsInstalled Adhesive Anchors
IBC 2006§104.11
IBC-ES AC308Design and Product Approval
30University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Design and Product Approval of Design and Product Approval of PostPost--Installed Grouted AnchorsInstalled Grouted Anchors
§104§104.11
Currently not covered by ICC-ES Acceptance Criteria
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31University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
ACI Consensus Standard StatusACI Consensus Standard Statuson Bonded Anchorson Bonded Anchors
• Adhesive anchor design provisions have been balloted by ACI 318 Sub B
• An adhesive anchor product approval standard is in the ACI 355 balloting process
• Grouted anchors need to be included• The goal is to have ACI consensus
standards issued by 2011.
32University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Design and Product ApprovalDesign and Product ApprovalConsiderationsConsiderations
• Grouted anchors are currently not covered by ICC-ES AC308
Today’s Design and Product Today’s Design and Product Approval of Bonded AnchorsApproval of Bonded Anchors
62University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
• The following presents background information on behavior, design and product approval of bonded anchors
• Specific design requirements for adhesive anchors are now in ICC-ES AC308 and being balloted by ACI 318
• Specific product approval requirements for adhesive anchors are in ICC-ES AC308 and being balloted by ACI 355
• Grouted anchors are currently not covered by ICC-ES AC308
Background on Behavior, Design, and Background on Behavior, Design, and Product Approval of Bonded AnchorsProduct Approval of Bonded Anchors
63University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
How Bonded Anchors Transfer How Bonded Anchors Transfer Tension LoadsTension Loads
hef
NN
Threaded Rod Mortar Concrete
τ τ0
hef
NN
Threaded Rod Mortar Concrete
τ τ0
Eligehausen et. al., 2004
64University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Potential Embedment Failure Potential Embedment Failure Modes of Bonded Anchors Modes of Bonded Anchors
Cook et al, 1998
65University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Bond Failure at Steel/Mortar Interface Bond Failure at Steel/Mortar Interface (Grout or Adhesive)(Grout or Adhesive)
The presence of the shallow cone has been shown to be secondary, the strength is dependent on bond
66University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Bond Strength of Single Bonded AnchorBond Strength of Single Bonded AnchorUniform Bond Stress ModelUniform Bond Stress Model
bond efN d hτ π=τ
Nbond
hef
d
R. A. Cook ACI Atlanta 2007 Hot Topic
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67University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Comparison of loads with the uniform bond modelComparison of loads with the uniform bond model(data set average bond stress normalized to 10 (data set average bond stress normalized to 10 MPaMPa))
0
100
200
300
400
500
600
0 10000 20000 30000 40000 50000 60000
Load
(KN
)
measured loadsmean - uniform bond model5% fractile - uniform bond model
Bond Area (A b ) (mm2)
Only 17 of 891 data points below 5% fractile (1.9%)
Cook et al, 1998
68University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
• For adhesive anchors (d≤1.5d0), the bond strength can be based the nominal bond stress relative to the anchor diameter (τ)
• For grouted anchors (d>1.5d0), the bonsstrength needs to consider both the nominal bond stress at the anchor/grout interface (τ) and at the grout/concrete interface (τ0)
71University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Design of Bonded AnchorsDesign of Bonded Anchors
• Bond strength can be based on the uniform bond stress model up to hef/d of ~20.
• Strength is limited to the concrete breakout strength as provided in ACI 318-05 Appendix D
72University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Behavior of Bonded AnchorsBehavior of Bonded Anchors
Anchor diameter (d)
Tens
ion
Load
' 1.5c efN k f h=
efN d hτ π=
Bond failure Concrete breakout failure
R. A. Cook ACI Atlanta 2007 Hot Topic
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73University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Critical Spacing and Edge Distance Critical Spacing and Edge Distance for Bonded Anchorsfor Bonded Anchors
0.5 scrs1
s2
ca1
ca2
AN = (ca1 + s1 + 0.5 scr)(ca2 + s2 + 0.5 scr)if ca1 and ca2 < 0.5 scrand s1 and s2 < scr
0.5 scr
0.5
s cr
0.5
s cr
2cr0N sA =
0.5
s cr
0.5 scr
a) Single anchor away from edges and other anchors
b) Four anchor group with close spacing and located near a corner
0.5 scrs1
s2
ca1
ca2
AN = (ca1 + s1 + 0.5 scr)(ca2 + s2 + 0.5 scr)if ca1 and ca2 < 0.5 scrand s1 and s2 < scr
0.5 scr
0.5
s cr
0.5
s cr
2cr0N sA =
0.5
s cr
0.5 scr
a) Single anchor away from edges and other anchors
b) Four anchor group with close spacing and located near a corner
74University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Critical spacing and edge distanceCritical spacing and edge distance
Cast-in-place and post-installed mechanical anchors:
Bonded anchors:
2 3.0cr cr efs c h= =
Why the difference?
0.5
2 201450cr crs c d τ⎛ ⎞= = ⎜ ⎟⎝ ⎠
Eligehausen et al 2006
ACI 318-05 Appendix D
75University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
For bond failure, embedment length For bond failure, embedment length does not have the same effect as that does not have the same effect as that for postfor post--installed mechanical anchors installed mechanical anchors
N
N
hef =20d
hef=10d
Appl and Eligehausen 2005
76University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
For bond failure, bond strength has a For bond failure, bond strength has a significant influence on critical spacingsignificant influence on critical spacing
1390 psi [9.9 MPa]τ =
2850 psi [19.6 MPa]τ =
Appl and Eligehausen 2005
77University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering
Strength of Bonded Anchors:Strength of Bonded Anchors:
, , ,0
Ncbond group ec N g N bond
Nc
AN NA
ψ ψ=
bond efN d hτ π=0.5
2 201450cr crs c d τ⎛ ⎞= = ⎜ ⎟⎝ ⎠
But not greater than the concrete breakout strength calculated by ACI 318-05 Appendix D Eq. (D-5)
Eligehausen et al 2006
78University of FloridaUniversity of FloridaDepartment of Civil EngineeringDepartment of Civil Engineering