The American Concrete Institute (ACI) standard titled Building Code Requirements for Structural Concrete (ACI 318) includes provisions for reinforced concrete design. ACI 318-19 Section 22.9 is titled Shear friction. This paper will discuss the provisions given in ACI 318-19 Section 22.9 with respect to shear transfer across an interface between an existing concrete surface and a new concrete surface. The design premise is that reinforcing bars designed to yield on each side of this interface will clamp the two concretes together, thereby permitting shear transfer across the interface.         

Section 22.9 provisions are written for the design of cast-in reinforcing bars; however, "post-installed" reinforcing bars can also be designed with these provisions. This is done by using an adhesive product capable of achieving bar "development," i.e., embedding a bar deep enough to "develop" the yield strength without splitting failure occurring. "Splitting failure" refers to cracking and splitting in the concrete around bars in tension. "Post-installing" a reinforcing bar consists of (1) drilling a hole into existing concrete, (2) injecting an adhesive product into the hole, and (3) inserting the bar into the adhesive-filled hole. An adhesive product capable of achieving bar development must be suitable for injection into holes having an embedment deep enough to develop the bar's yield strength without splitting failure. These products must also exhibit stiffness characteristics that permit bar development versus concrete breakout failure or bond failure. For an adhesive product to be used to post-install reinforcing bars designed per ACI 318 development provisions, the adhesive "system" must be evaluated to determine if it performs equivalently to cast-in reinforcing bars designed for development. Hilti adhesive products are evaluated as a system consisting of the adhesive product, the anchor element being used (e.g., threaded rod, reinforcing bar, etc.), and the installation method (e.g., hammer drilling, hole cleaning procedure, etc.). Hilti adhesive anchor systems are evaluated per the International Code Council Evaluation Service (ICC-ES) acceptance criteria, Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete Elements (AC308). The evaluation is done to (a) demonstrate compliance with the International Building Code (IBC) and (b) obtain data for designing the adhesive anchor system using ACI 318 provisions. Adhesive products that satisfy the provisions of the test program outlined in AC308 Table 3.8 can be used to post-install reinforcing bars designed per ACI 318 development and splice provisions. Since ACI 318 shear friction provisions are also predicated on bar development,  Hilti adhesive products that have been evaluated per AC308 Table 3.8 can be designed for shear friction per the provisions given in ACI 318-19 Section 22.9.    

Summary

The shear friction provisions in ACI 318-19 Section 22.9 can be used to design reinforcing bars post-installed with an adhesive product. The adhesive, reinforcing bar, and installation procedure must be evaluated as an overall system to determine if performance equivalent to cast-in reinforcing bars designed for development can be achieved. Hilti adhesive systems that have been evaluated per the test programs given in the ICC-ES acceptance criteria AC308 Table 3.8 can be used to design post-installed reinforcing bars with ACI 318-19 shear friction provisions. The attached file shows the post-installed reinforcing bar design per the shear friction provisions given in ACI 318-19 Section 22.9.

You can learn more about Post-Installed Reinforcing Bar design by referencing the following:

Hilti Post-Installed Reinforcing Bar Design Guide

Click on this link to access Post-installed Reinforcing Bar Design Guide

Hilti Design Software

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Open the Anchoring-to-Concrete module for design using ACI 318 anchoring-to-concrete provisions.

Open the Concrete-to-Concrete module for design using ACI 318 reinforcing bar development provisions.

Hilti Post-Installed Rebar White Papers

* Post-installed Reinforcing Bar Design Options: An Overview

* Shear Friction Design using the Hilti Method for Post-installed Rebar Design

* Design for Yield using Anchoring-to-Concrete Provisions for Post-installed Reinforcing Bar Design
* Extension Design using ACI 318-19 Provisions for Post-installed Reinforcing Bar
* Structural Joint Design using ACI 318-19 Provisions for Post-installed Reinforcing Bar
* Shear Friction using ACI 318-19 Anchoring-to-Concrete Provisions for Post-installed Reinforcing Bar Design
* Shear Friction using ACI 318-19 Provisions for Post-installed Reinforcing Bar Design