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?

 

[hokie66]

I always wonder how they get rebar to develop with a thin skin of adhesive in a much shorter distance than in the concrete. I don't buy it.

 

[Archie264]

Hokie66, out of curiosity, have the Australian codes imposed something similar to the notorious Appendix D that the haynewp mentioned? Just curious, that's all.

 

[hokie66]

No, not to my knowledge.

 

[Archie264]

Ah, thanks for the info. I was trying to get a feel for state of the industry, whether everyone's going down that road, or what the situation might be. That particular appendix is a lot to deal with but I'm willing to accept it if it really is an improvement, justified, or needs to be that complicated...that type of thing. When I hear that others are getting along just fine without it, well, it makes me sigh.

 

[hokie66]

This investigation report supports my intuitive reasoning that adhesive anchorage of reinforcement should be at least as long as when cast in. Not sure of the date.

http://129.69.59.201/bibliothek/festschr/eligeh.pdf

 

[haynewp]

Requiring full concrete bond would eliminate Hilti and Simpson adhesives and all their testing. That's a large statement.

 

[TXStructural]

hokie, I keep telling people this, but they always say "the manufacturer says..." The other side of the equation is how the force in the bar gets into the next length of reinforcement. Since these are presumably tension forces, they have to be put into other tension ties or compression struts, either of which would require full development length (or possibly an Ldh as with a headed anchorage.)

 

[msquared48]

I think that it points to a basic difference between a mechanical bond (straight embedment with air voids in the concrete) and a chemical bond (where there are no air voids). Same force in less embedment length. That would have to mean that the shear cone would be critical in a chemical bond, not the bond itself.

Just a thought...

Mike McCann
MMC Engineering

 

[hokie66]

But Mike, read the report of this investigation. The critical testing in haynewp's case is with the concrete restrained by a plate, therefore no cone is possible. And as the authors stated, there is much more room for error with chemically anchored bars than there is with those which are built in.

Haynewp, I don't eliminate chemical anchors, especially for shear. But I think their marketing has been based on half truths, and I don't mind making that "large statement".

 

[rowingengineer]

I agree with Hokie, I can't understand how this can be. sounds like black magic, use this stuff and all your problems disappear.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[haynewp]

I think they have to show test data based on ACI requirements in order to get ICC approval for their chemicals and what they are stating for lengths required to develop a bar. Without ICC approval they may not be legitimate for a certain mfr's product and maybe some are not being honest. It seems like they would say more length is required instead of less so they could sell more epoxy but I don't know.

But anyway, assuming the epoxy is correctly installed and inspected, and does actually develop the bar, it still seems to me like blowouts by Appendix D could occur for short embedment lengths. But then I can't find where there are any minimum edge distances to preclude blowouts under the shear friction section which doesn't seem right either even when you are using the longer concrete bond development lengths.

 

[hokie66]

This manufacturer says some of its competitors give misleading advice. Admittedly, its researchers are the same ones who did the report referenced above.

http://www.fischer.sg/PortalData/1/...s/connectit/_documents/04-connectit-01-en.pdf

 

[msquared48]

Hokie:

It is nowhere near as apparent to me as it is to you. I will print out the paper though on Monday and read it in depth as I have time.

That being said though, this would be an excellent opportunity for you to write a paper and submit it to Ron's new site for further peer discussion. Just a thought.

Cheers. Have a good weekend.

Mike McCann
MMC Engineering

 

[wannabeSE]

I am confused. I thought appendix D is needed to calculate the capacity of reinforcing embedded in epoxy/adhesive. Do any reputable manufactures have other methods that ignore the concrete failure modes in Appendix D? If I am not mistaken ACI 355.4, Qualification of Post-Installed Adhesive Anchors in Concrete, is coordinated with Appendix D. Is there another ACI standard for adhesive embedded reinforcing? Is anyone disputing the capacity of epoxy embedded reinforcing when Appendix D is used?

For the original question concerning shear friction with epoxy embedded reinforcing, I assume the equation used is V_n = A_vff_yμ. Wouldn't one use Appendix D and the manufactures evaluation reports to determine the tension capacity for the A_vff_y used in the shear friction equation.

 

[hokie66]

There is a recent paper about the subject, proposing a design method for users of the ACI Code. I haven't accessed it or read it, but perhaps someone (TXStructural?) can give us a capsule summary.

http://www.concrete.org/PUBS/JOURNALS/AbstractDetails.asp?ID=51685601

 

[haynewp]

Prior to IBC 2012 (which I was not using for this project), adhesive anchors were excluded from Appendix D. Reinforcing used for embedment was required to be designed by "other parts of this Code" per ACI Appendix D, D2.2. By that abstract link above, epoxied reinforcing is still not part of Appendix D.

 

[hokie66]

Which to me means that there is no difference between reinforcement embedment requirements with or without epoxy...by your current Code.

 

[DaveAtkins]

I have always looked at this like TXStructural. Yes, epoxy can develop a bar with a short embedment length into existing concrete, but the problem is the bars in the existing concrete are not developed.

DaveAtkins

 

[UcfSE]

That the bars in the existing concrete are not developed is no mystery, and nothing new. If you need those bars, then you need to develop them such that force can transfer from the new bar to the existing bar. Typically that means much greater embedment depths for the new bar. Then you meet the depth to develop the new bar, and you have the development to get the existing bar as well. It's not the manufacturer's fault that many people overlook this.