Post-Installed Reinforcing Bar Guide

6.0 WHAT ’ S THE BACK STORY ?

ψ _{ec} _{,} _{N}

ψ _{c} _{,} _{N}

ψ _{cp} _{,} _{N}

λ _{a}

k _{c}

h _{ef}

Factor to account for eccentrically-loaded groups Increase factor that accounts for uncracked concrete Factor to account for splitting hoop stresses Lightweight concrete adjustment factor

Efficiency factor for concrete breakout ( characteristic value , cracked concrete ); for adhesive anchors , this value is determined by testing in accordance with ACI 355.4 .

Effective embedment depth in inches

Similarly , in accordance with ACI 318-19 Section 17.6.5.1 , the characteristic bond strength , N _{ag}

, of adhesive anchors in cracked concrete is determined as shown in equation 13 :

N _{ag}

where

A _{Nca}

= ( 2c _{Na}

) ^{2}

A _{Na}

c _{Na}

cr

d _{a}

uncr

= ^{A} Na ANao

Projected influence area based on critical anchor edge distance , c _{Na}

= 10d _{a} ψ _{ed} _{,} _{Na} ψ _{ec} _{,} _{Na} ψ _{cp} _{,} _{Na} uncr

1100

( in ) cr λ _{a} πd _{a} h _{ef}

( lb ) ( Eq . 13 )

Characteristic bond stress in cracked concrete per evaluation in accordance with ACI 355.4

Characteristic bond stress in uncracked concrete per evaluation in accordance with ACI 355.4

Diameter of anchor element ( threaded rod , reinforcing bar )

Other terms are analogous to the expression for concrete breakout .

Strength reduction factors ( ϕ ) given in ACI 318-19 Tables 17.5.3 ( a , b & c ) are applied to the nominal steel , concrete breakout , and bond strengths , and the minimum value is compared to the factored design load N _{ua}

. Additional design checks are made in accordance with ACI 318-19 Section 17.5.2.2 for adhesive anchors subjected to sustained tension loads . Where anchors are used in structures assigned to Seismic Design Categories C , D , E or F , additional requirements in accordance with ACI 318-19 Section 17.10 are placed on the anchor behavior .

According to ACI 318-19 R25.4.2.4 , splitting governs the behavior of reinforcing bars placed at minimum cover with no transverse or other confining reinforcement . Bars placed with increased cover and / or provided with transverse reinforcing are governed by pullout failure , but , it is noted , “… an increase in cover or transverse reinforcement ( beyond that assumed to ensure pullout behavior ) is unlikely to increase the anchorage capacity .” Note that in no case is concrete breakout anticipated , regardless of the density of bars placed in a specific volume of concrete . This assumption is likely predicated on the relatively low bond stresses associated with the development length equation ( see Figure 45 ). For post-installed reinforcing bars designed in accordance with anchor theory , however , the full tested bond strength of the adhesive is utilized and as such evaluation of both the bond and breakout capacities in accordance with ACI 318 is required .

Post-installed reinforcing bars can be designed by recasting the concrete breakout and bond strength expressions in ACI 318 into development length equations ; that is , by equating the strength associated with concrete failure or bond failure with the yield strength of the embedded bar and solving for the embedment . This may be particularly useful where cover ( edge distance ) is large but embedment depth is limited , such as the development of bars into the face of a wall .

Note : For additional information on this approach , see Charney , et al ., “ Recommended Procedures for Development and Splicing of Post-installed Bonded Reinforcing Bars in Concrete Structures ,” ACI Structural Journal , Vol . 110 , No . 3 , May-June 2013 [ 4 ].

Per Charney et al ., when a single post-installed reinforcing bar is installed in normal weight concrete away from edges such that the concrete break out strength is not affected by edge distance , the concrete breakout-associated embedment required to achieve yield in the embedded reinforcing bar may be expressed as shown in equation 14 :

l _{d} _{,} _{breakout}

= 1.2

Similarly , when a single post-installed reinforcing bar is installed away from any edges , the bond-controlled embedment required to achieve yield in the embedded reinforcing bar can be expressed as shown in equation 15 :

l _{d} _{,} _{bond}

=

0.3d _{b} f _{y} cr

A _{b} f _{y} k _{c}

2 / 3

( in ) ( Eq . 15 )

( in ) ( Eq . 14 )

The design development length for this particular case may be taken as the greater of and , l _{d} _{,} _{breakout} and l _{d} _{,} _{breakout}

, as shown in equation 16 :

l _{d} _{,} _{bond}

= max | l _{d} _{,} _{breakout} ; ^{l} d , bond ^{|}

( in ) ( Eq . 16 )

Note : Eq . 14 and Eq . 15 may also be derived using the CSA provision wherey the ratio of the resistance modification factors can conservatively be taken as 1.0 ."

29 2021