Seismic foundation multi-story braced frame

[ugandabob]

thread507-496992

Similar to what was discussed in a previous thread, I am looking for guidance related to the overturning capacity of a steel multi-story braced frame. I'm worried I'm being overly conservative, but looking for a sanity check. My initial interpretation is that the overturning capacity is based on the story forces that allow the braces in each story to achieve their capacity (buckling or tension, depending on the system) at the same time. I do not think this is a realistic scenario, but it still seems like it is technically the capacity of the frame.

I am trying to avoid designing the foundation and anchorage for the forces related to RdRo = 1.3 because they are very large on a current project, so designing for the capacity of the system may be beneficial.

So, is my approach correct? Or would it be more reasonable to base the overturning capacity on the forces required to yield one story only?

I cannot find any papers or literature that address this clearly.

Thank you.

 

[driftLimiter]

This issue is a bit of a conundrum at least with US codes.

The code languages suggest you design the foundation system for a different level of loading than the frame. Common statics suggests that that is ridiculous and equilibrium must be maintained.

Here is an old thread where it was somewhat discussed. Old Thread

Here is a paper with some commentary on it that leans toward designing the foundation for amplified forces. BRBF Paper