Retrofit Concrete Anchors
Retrofit Concrete Anchors
(OP)
I've been struggling w/ the design of retrofit concrete anchors using the Simpson and Hilti software packages, and am wondering what the rationale is for why you can't increase the anchor embedment length of the anchor to the point at which you can satisfy the ductility requirements of Appendix D?? If your embedment depth is limited, it forces you to increase the anchor diameter in order to achieve the required adhesive bond strength, which then drives up your required anchorage force due to ductile failure of the anchor itself. Seems like a catch-22, and one that I don't agree with. I could see that if you were specifying a 1/2" dia. anchor that was 8 ft. long you wouldn't necessarily be able to activate the rod at it's very end, but the embedment values that you can specify in the anchor design programs seems to be VERY conservative. Does anyone know what that stems from? Thanks!





RE: Retrofit Concrete Anchors
I don't know the US ACI Appendix D, but from everything I've read it is nothing but trouble for Yank engineers... I would hope that your local building authority will permit an alternate method. Ask them.
RE: Retrofit Concrete Anchors
RE: Retrofit Concrete Anchors
RE: Retrofit Concrete Anchors
I've used the Hilti program quite a bit and have certainly found some instances of them being a bit overly conservative. But, I think for a free program that deals with a some very complex calculations with a very user friendly interface, it's actually a really good program. I've often called technical support and they have often either given me where in the code it states why they are doing something or explained the research that went into it. If I believe their response is overly conservative, I have done hand calcs to prove why I'm doing meets code (there are a few things that are recommendations that Hilti will not permit).
Appendix D is an extremely tough code, however after the Big Dig collapse, ACI (along with the big players in anchorage) needed to specify the required calculations in a more complex way. I've wondered whether Hilti/Simpson had some ulterior motives when they 'helped' aci develop these codes... but I digress
If I were you, I'd call Hilti and ask them about the limit.
RE: Retrofit Concrete Anchors
RE: Retrofit Concrete Anchors
Maybe I am lucky, but Simpson (anchor products) and Hilti have experienced local field engineers who are very responsive end easy to contact. If they don't know the answer, they know who to ask.