Epoxy dowel & shear friction 1

[haynewp]

If rebar is developed on either side of the shear plane, one side being with epoxy that develops the rebar with the epoxy but not long enough to develop the rebar if it was in bond with concrete only, should you be able to use shear friction by ACI or be forced to the concrete breakout checks in Appendix D?

 

[haynewp]

I'm just trying to create a shear connection, not develop any existing bars.

 

[TXStructural]

You cannot use shear friction unless the bar is fully developed on both sides of the shear plane, as you alluded to in your original post. The 318-11 11.6.8 language is "...shall be anchored to develop fy on both sides by embedment, hooks, or welding to special devices." The commentary says, in part, "Anchorage may be developed by bond...", which is slightly different from embedment. The mechanism required by 318-11 11.6.8 is tension in the reinforcement, without mention of direct shear transfer.

Appendix D offers a method to determine how well a post-installed anchor will resist forces. If the design considers all parts of the system and the load path is continuous and sufficient, the design would comply with the code.

 

[haynewp]

I guess the question that has come up after my original question, since we have found out that expoxied rebar is not included in Appendix D, is this:

Are the short rebar embed lengths (as what is being provided by adhesive manufacturers) using epoxy to develop the bars accepted by Code through testing?

 

[haynewp]

I think the answer is "yes" if it goes through the ICC testing:

http://www.icc-es.org/News/news-ac.shtml

Here are 2 reports that include rebar, oddly enough they appear to use Appendix D as part of the reports:

http://www.icc-es.org/Reports/pdf_files/ESR-2508.pdf

http://www.icc-es.org/Reports/pdf_files/ESR-2322.pdf

 

[TXStructural]

The short answer is "no". The length of embedment that is required to bond bar to concrete is not the length required to comply with either Appendix D (which considers everything EXCEPT adhesive bond), or anchor the bar sufficiently to other reinforcement using development length. The method for determining adequate anchorage is Appendix D. If the adhesive (which is usually acrylic rather than epoxy) is tested to develop full bar yield strength along a length, AND the tables or software ALSO consider the Appendix D computations, then it should be good.

That said, short embedments using chemical anchors are MINIMUMS. There is no reason to adhere unreasonably to a minimum when life safety and structural integrity are on the line. You do not want to be excessive, but think the entire anchorage through carefully - it is the job of an engineer to use engineering judgement, not just get away with a minimum number published by a manufacturer. Look at supporting data and testing, understand the issues, and make an engineering decision. There is very little economy in minimal design, when a slightly deeper embedment of a limited number of bars eliminates all concern. We frequently spend lots of hours researching and discussing, when a more robust design solves the problem and costs less.