Rebar Knowledge Center Design as an “Anchor” or “Reinforcement”?

POST-INSTALLED REBAR: DESIGN AS AN “ANCHOR” OR
“REINFORCEMENT”?
The difference between designing post-installed rebar using anchoring-to-concrete
provisions and using reinforcement development provisions.
Adhesive anchors have been extensively used in construction since the mid-1970s. In the United States,
building code provisions governing adhesive anchor systems are regulated by the American Concrete
Institute (ACI) codes and standards, including ACI 318 and ACI 355.4. Canada is regulated by the Canadian
Standards Association standard CSA A23.3. Adhesive anchor systems in the United States are also
evaluated according to acceptance criteria issued by the International Code Council Evaluation Service (ICCES). Adhesive systems for concrete base materials typically have employed threaded steel rod or rebar as
an anchor element for design using the anchoring-to-concrete provisions of ACI 318. Recent revisions to the
ICC-ES Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete Elements (AC308) have made it
possible for an adhesive system to be approved for post-installing reinforcing bars per the development and
splice provisions of ACI 318. Therefore, adhesive systems qualified per the provisions of AC308 can now be
used with post-installed reinforcing bars that are designed per the anchoring-to-concrete provisions of ACI
318 and per the development and splice provisions of ACI 318.

Design Methodology
So, what is the difference between designing post-installed rebar using anchoring-to-concrete provisions
versus using reinforcement development provisions? The methodology for designing post-installed
reinforcing bars using the anchoring-to-concrete provisions of ACI 318 is different than the methodology for
designing post-installed reinforcing bars using the development and splice provisions of ACI 318. When postinstalled reinforcing bars are designed using ACI 318 anchoring-to-concrete provisions, design strengths (φN n
or φV n ) corresponding to possible tension or shear failure modes are calculated and checked against factored
tension or shear loads (N ua or V ua ) acting on the bars. When post-installed reinforcing bars are designed
using ACI 318 development and splice provisions, they are designed for development, i.e. designed to yield.
Bars designed to yield must be embedded deep enough to preclude splitting failure. The test program
outlined in Table 3.8 of AC308 includes assessment of an adhesive system for post-installing reinforcing bars
to an embedment as deep as 60d bar . Post-installed reinforcing bars can be developed at this embedment.
Compare this embedment to the maximum embedment of 20d bar permitted in ACI 318 anchoring-to-concrete
provisions. Post-installed reinforcing bars typically must be installed at an embedment greater than this in
order to be developed. In addition, post-installed bars embedded deep enough to be developed are capable
of transferring a tension or compression force acting on the bar to an existing bar via a lap splice. Anchoringto-concrete provisions do not consider lap splices.
Therefore, if your design intent is to ignore bar development and design the bar as an adhesive “anchor”, you
would typically design using the anchoring-to-concrete provisions of ACI 318; e.g. ACI 318-11 Appendix D or
ACI 318-14 Chapter 17. On the other hand, if your design intent is to develop the bar or to design a lap splice
for transferring loads to existing reinforcement, you would typically design using the development and splice
provisions of ACI 318; e.g. ACI 318-11 Chapter 12 or ACI 318-14 Chapter 25. Adhesive systems qualified
per AC308 receive recognition under the International Building Code (IBC) via an ICC-ES evaluation service
report (ESR). Since the IBC references ACI 318, an adhesive system having an ESR resulting from
qualification per AC308 can then also be used to design post-installed reinforcing bars with ACI 318
provisions for anchoring-to-concrete and for development/splicing.
Adhesive systems qualified per AC308 Table 3.8 can be used to design a post-installed reinforcing bar for
development per the development and splice provisions of ACI 318. Bars can de designed for either tension
or compression development at embedments up to 60d bar . Adhesive systems qualified per AC308 Table 3.2
can be used to design a post-installed reinforcing bar as an anchor element per the anchoring-to-concrete
provisions of ACI 318. Note that anchoring-to-concrete design permits consideration of both a tension load as
well as a direct shear load acting on a bar, but the maximum embedment depth is limited to 20d bar .