Column braced frame base plate to foundation connection
Column braced frame base plate to foundation connection
(OP)
For the base plate to foundation connection at braced frame columns, what order of magnitude for tension do you consider significant enough to warrant a more robust connection than just anchor bolts and shear plates? I'm working on a project that has around 450 kips net uplift (ULT). I'm considering slightly recessing the column into the footing to transfer shear through bearing. For the large uplift I was thinking weld plates from the base plate to an embed plate. The embed plate would have welded rebar with hooks to fully develop the tension. Others in the office think this may require something even more robust. I appreciate your input in advance. Thanks.






RE: Column braced frame base plate to foundation connection
RE: Column braced frame base plate to foundation connection
1) Interior footing condition?
2) Any grade beams connecting your footings to other stuff?
3) Column connection is directly to footing? No pier / pedestal?
4) You're assuming that shear is resisted by friction at the underside of the footing and or passive soil resistance on the side?
5) Wide flange column?
6) What seismic class of braced frame? Special? Intermediate? Ordinary?
A big concern in these situations is uplift punching shear in the footing. If you go with hooked welded rebar, you'll need to give the punching shear force transfer mechanism some serious thought. More on that once we've got a better picture of what's going on.
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: Column braced frame base plate to foundation connection
KootK
1) yes
2) I will use some tie grade beams but this is to engage more dead load to resist sliding through friction.
3) yes
4) I'm assuming sliding is resisted by friction between the footing base and the soil.
5) yes
6) using "steel systems not specifically detailed for seismic resistance" SDC is "B"
RE: Column braced frame base plate to foundation connection
RE: Column braced frame base plate to foundation connection
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: Column braced frame base plate to foundation connection
RE: Column braced frame base plate to foundation connection
1) I should have shown the base plate extended under the gusset plate and welded to it.
2) You either have to separate the anchor bolts and embedded plate such that their failure cones do not over lap OR you have to give some consideration to the fact that the do over lap.
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: Column braced frame base plate to foundation connection
Kootk, thanks I picked up on that.
One point I would like to further discuss is both KootK your detail and mike20793 your NEHRP recommendation both show a plate recessed to the bottom of the footing and basically resisting tension by a punching shear approach. Logically this makes sense to me, but we are basically saying don't worry about ACI Appendix D. If we were to consider Appendix D our capacities would be significantly less. In fact mike20793, for your latest detail that you sent I don't know how you were be able to resist 490 kips tension by Appendix D.
Thanks again gentlemen.
RE: Column braced frame base plate to foundation connection
Definitely throwing out appendix D. Although, with my detail, I suppose it would technically be a hybrid. Appendix D for the embed shear plate and another approach for the tension. I don't feel that appendix D is really a suitable tool for the kind of loads that you're dealing with.
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: Column braced frame base plate to foundation connection