Moment frame foundation design 3

[333OnlyHalfEvil]

When designing a moment frame what is the procedure for doing the foundation? I’ve seen people do a “rolling” (idk how to describe it) calc where they have a triangular pressure for the soil bearing. Do you know what I’m referring to? Is this the right way? Thoughts? Can someone point me in the direction of a good resource regarding moment frame design/calcs? Thanks.

 

[phamENG]

Depends on how you're restraining the moment frame. Fixed base or pin? Single footing or one for each column?

Individual footings are straightforward - so I'm assuming that's not what you have.

Single footing is a bit more complicated. I know what you mean by the 'rolling' foundation - where you just put the moment from the moment frame on the footing and call it good. For very small moment frames resisting wind in a single story house, sure...it might work well enough...but anything larger/more consequential I wouldn't do it that way. For that to work, the stiffness of the foundation would have to be pretty incredible. So for a really short moment frame, it can be plausible. But you'd need to look at flexure in the concrete as well as uplift loading and down-loading from gravity loads and the frame action resisting the lateral loads. Look into beams on elastic foundations - there are some relatively simple numerical approximations you can use.

If you have a single footing with pinned bases, you'll just have shear and vertical loading. For that I might try superposition with a more traditional footing analysis. Look at the loading from each column separately and apply them to the foundation. Then superimpose them to see what the actual bending moment and shear diagrams look like for the footing, as well as bearing pressures.

 

[HTURKAK]

I will suggest you to look section ( 5.5 BASE FIXITY ) of the following document.

https://www.steelconstruction.info/images/4/44/SCI_P252.pdf