Foundation loads for seismic/wind design

[Sanira]

Do we need to consider any amount of minimum seismic load and wind load for gravity only elements? I have a podium building with steel braced frames on the first floor. Do we only consider seismic/wind forces for the foundation design of braced frames or do we need to consider it for other foundations in the building supporting gravity elements only? Furthermore, what are the design loads we need to consider for the design of the foundation?

Thank you.

 

[msquared48]

If your "element" is truly gravity only, then no, but its connections could see some laterally induced forces.

Any element in the foundation that sees lateral loads (earth included) will also potentially see seismic loads. However, wind may control over seismic.

The design loads to consider depend on your occupancy, your location, the height of the building, the topography, the type of lateral resisting system and a whole other host of considerations. There is no one answer here. You have to read the code pertaining to your structure.



Mike McCann, PE, SE (WA, HI)

 

[JAE]

There's this concept in structural design called "deformation compatibility".

If you have a "gravity" column/footing but under wind/seismic forces the entire frame sways sideways, you, as the designing engineer need to ensure that the non-participating column/footing can tolerate those drifts.

Usually for wind, the drifts aren't really significant to worry about but for seismic they can be quite large.

Also, in the US codes for seismic, there is a vertical seismic effect in the load combinations that would be applied also to "gravity" columns.

 

[r13]

Unless your building is exempted for seismic consideration, the "element" is going to experience inertia forces (lateral and vertical) during an earthquake event no matter how it is attached to the building. However, depending on where this element is situated, and details of its joints to the surrounding building components, wind may, or may not affects the foundation design. Finally, a foundation is to be designed for all type of loadings a structure/building is subjected to, including DL, LL, snow load, wind load, seismic effects, static/dynamic soil pressures, and hydraulic forces, if applicable. Now, just for curiosity, can you provide more details of this "gravity only element"?