PostInstalled Reinforcing Bar Guide
6.0 WHAT ’ S THE BACK STORY ?
6.6.1 DESIGN OF POSTINSTALLED REINFORCING BARS USING ANCHOR DESIGN CONCEPTS ^{17}
The use of anchor design concepts for determining the embedment of postinstalled reinforcing bars is discussed in the literature and is appropriate for systems that have also been qualified under anchor qualification provisions ( e . g ., ACI 355.4 , AC308 ). The use of anchor design concepts is relatively straight forward , but appropriate assumptions are required with respect to the embedment . For example , is achievement of bar yield required ? If so , should over strength be applied to the nominal bar yield stress ? The answers to these and other questions are situation dependent .
This approach can be subdivided into two categories :
Category 1 — Bars installed far away from edges in the face of walls , slabs , and foundations . In this case , postinstalled reinforcing bars are assumed to be located sufficiently far from any edge to preclude splitting failure . Concrete breakout and bond resistances are likewise assumed to be unaffected by edge conditions .
Category 2 — Bars installed away from edges but still potentially affected by edge distance when determining the concrete breakout strength . The use of anchor design concepts is still possible in such cases , but is complicated by the edge proximity and requires iteration to find an optimal solution .
ACI 31819 Section 17.5.1.2 specifies that the design strength for adhesive anchors in tension be taken as the minimum value of the steel , concrete breakout and bond strengths as determined for a given bar diameter and anchorage length ( embedment depth ), including the appropriate strength reduction factors , and limits the uniform bond model that is the basis for the design provisions to embedment depths between 4 and 20 anchor diameters . Beyond 20 diameters ,
120 the nonlinearity of the bond stress distribution can lead to a reduction in the usable bond stress at failure that must be assessed with engineering judgment .
The nominal steel strength in tension , N _{sa}
, of a single anchor element ( e . g ., threaded rod or reinforcing dowel ) is determined per Eq . ( 17.6.1.2 ) of ACI 31819 as the product of the tensile stress area of the anchor element and the anchor element nominal ultimate strength . ACI 318 notes that the ultimate strength is used because many anchor elements do not exhibit welldefined yield plateaus . As such , a limit of 1.9f _{y} is placed on the value of the nominal ultimate stress that can be used in Eq . ( 17.6.1.2 ) in order to avoid yielding of the anchor element at service load levels . In the case of reinforcing bars , the nominal yield strength is not generally well controlled . Generally speaking , yield strengths may exceed specified values by 25 %. ASTM A706 Grade 60 bars are controlled such that the actual tested yield cannot exceed 78 ksi , and the tested ultimate cannot be less than 125 % of the actual yield . ^{18}
In accordance with ACI 31819 Section 17.6.2.1 , the nominal concrete breakout strength in tension of headed anchors is obtained as shown in equation 12 :
N _{cbg}
where f ' _{c}
120
Concrete compressive strength in pounds per square inch ( psi )
A _{Nco}
9 ( h _{ef}
) ^{2}
A _{Nc}
ψ _{ed} _{,} _{N}
= ^{A} Nc ANco ψ _{ed} _{,} _{N} ψ _{ec} _{,} _{N} ψ _{c} _{,} _{N} ψ _{cp} _{,} _{N} k _{c} λ _{a}
( h _{ef}
) ^{1} ^{.} ^{5}
( lb ) ( Eq . 12 )
Projected area of theoretical breakout body based on critical anchor spacing of 3h _{ef} and anchor edge distance of 1.5h _{ef}
Factor that accounts for nearedge anchors that reflects the disturbed stress state caused by the presence of an edge
100 100
Stress [ ksi ] 
80
60

# 3 bar 
Stress [ ksi ] 
80
60

# 5 bar 

40 


40 


20 


20 

0 0 0.01 0.02 0 . 03 0.04 0.05 0 . 06 0.07 0 . 08 0.09 0.1 Strain [ in / in .]
Figure 46 — Stress strain curves for # 3 and # 5 ASTM A706 Gr . 60 reinforcing bars . ^{19}
0 0 0.01 0.02 0 . 03 0.04 0.05 0 . 06 0.07 0 . 08 0.09
Strain [ in / in .]
17 ) Charney , F ., et al ., “ Recommended Procedures for Development and Splicing of Postinstalled Bonded Reinforcing Bars in Concrete Structures ,” ACI Structural Journal [ 4 ]. 18 ) ASTM Standard A706 / A706M , 2014 , “ Standard Specification for Deformed and Plain LowAlloy Steel Bars for Concrete Reinforcement ,” ASTM International , West Conshohocken , PA ,
2003 , DOI : 10.1520 / A0706 _ A0706M , www . astm . org . 19 ) Publication No . FHWAHIF13038 , “ Laboratory Tests of ColumntoDrilled Shaft Socket Connections ,” Federal Highway Administration , June 2013 , p . 11 .
28 2021