Product Technical Guides : US-EN Post-Installed Rebar Guide - Page 29

Post-Installed Reinforcing Bar Guide
6.0 WHAT ’ S THE BACK STORY ?
Equivalent ( uniform ) bond stress values corresponding to development lengths determined in accordance with ACI 318-19 are shown in Figure 45 :
Bar size
Concrete Compressive Strength ( psi )
3000 4000 5000 6000 7000 8000 ≤ # 6 570 658 735 806 870 930 ≥ # 7 456 527 589 645 697 745
Figure 45 — Equivalent bond strengths ( psi ) for uncoated bars developed in accordance with ACI 318-19 Section 25.4.2.4 in normal weight concrete with ( c b
+ K tr )/ d b
= 2.5 .
In the absence of confining reinforcement , the confinement term achieves the limiting value when the ratio of c b to db equals 2.5 . Theoretically , the development length of a reinforcing bar with cover equal to or greater than 2.5d b is no longer controlled by splitting . Since practical considerations often dictate edge distances for post-installed reinforcing bars greater than 2.5d b
, the presence of transverse reinforcement is often not a factor for determining the development length .
6.6 ALTERNATIVE APPROACHES TO ESTABLISHING BAR EMBEDMENT
The development length provisions of the ACI code are predicated on the assumption that bars may be closely spaced and may be placed at cover depth from the concrete surface .
Limited reduction in development length is afforded for bars placed at or greater than 2.5d b away from edges , since it is assumed that pullout should control for these bars ( as opposed to splitting ). Increases in edge distance should permit further reductions in development length ; however , closely spaced bars carrying higher bond stresses could lead to concrete breakout failure , a failure mode not anticipated in the development length formulation .
However , when post-installed reinforcing bars are not lapped with existing reinforcing and are installed sufficiently far from edges , it may be appropriate to employ other design approaches as described in the following sections .
27 2021