Concrete bearing capacity in bolt holes
Concrete bearing capacity in bolt holes
(OP)
Hi, I am designing steel bracket attachment to existing concrete using thru bolts. The bolts will be epoxied in the holes prior to installation. My question: are there recommendations for concrete bearing capacity in such situation?
Thank you all!
Thank you all!






RE: Concrete bearing capacity in bolt holes
RE: Concrete bearing capacity in bolt holes
ACI addresses bearing capacity on concrete, but makes no distinction between bearing due to say a baseplate versus bearing to a bolt or anchor rod. You may find something buried somewhere in Appendix D, but Appendix D does not apply to thru bolts.
I would simply use the bearing strength equation in section 10.14 of ACI 318.
RE: Concrete bearing capacity in bolt holes
As far as I'm concerned, there's functionally no such thing as through bolting. There's appendix D stuff for which I would absolutely grout/adhesive the hole and, if you need better pullout numbers, punching shear can be mobilized via the backside anchor plate if you have one.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Concrete bearing capacity in bolt holes
Professional and Structural Engineer (ME, NH)
American Concrete Industries
www.americanconcrete.com
RE: Concrete bearing capacity in bolt holes
Take a look at something like a mechanical expansion anchor. You drill a hole, insert the anchor and then engage the wedge at the bottom. That gives you an obvious tension load path, but your shear load path is some combination of that tension and shear capacity at the very bottom of the hole along with bearing along the normal anchor material that's been installed in a slightly oversized hole.
Realistically, this is the same situation you'd have in place with a through bolt. You have tension restraint and probably some friction at the bottom, and then bearing along the shaft.
Maybe investigate the technical documentation behind Hilti's Kwik Bolt? Their European technical stuff is more detailed than the North American stuff, maybe they go into their assumptions somewhere in that.
There are situations where I'd likely be comfortable using a through bolt with shear load without epoxying or grouting it. I'd want a large factor of safety on top of conservative assumptions, though, unless I can find good documentation of testing.