Combining flexible and rigid diaphragms in same system

[pyseng]

I'm currently working on a 4-story wood framed structure on a 1-story steel moment frame podium. I have no problem with the Two Stage Analysis Procedure and all those provision. However, I'm a bit stuck on the applicable lateral load cases. The issue centers around the idea that I have flexible diaphragms in my wood structure, and a rigid diaphragm on my steel podium. I have looked everywhere for some guidance on how to analyze a structure that contains both rigid and flexible diaphragms, but have found nothing.

The issue becomes the lateral load cases, in particular, the eccentric lateral load cases. There are a number of provisions that allow one to ignore the torsional/eccentric load cases in structures with flexible diaphragms. Ideally, I would like to be able to ignore the torsional wind load cases by amplifying the wind load on the wood structure by 1.5 as given in ASCE 7-10 Appendix D. But if the podium structure requires the torsional load cases, how do I include the wood structure's wind loads (same applies to the accidental eccentricity in the seismic loads)? Feels like I'm trying to fit a square peg into a round hole.

Thank you!

 

[r13]

I would not amplify the wind for either case, but to amplify the forces in the members affected by the rigid diaphragm to achieve code requirement on strength.

 

[jittles]

If you're doing the two-stage analysis procedure, you design the two portions separately so you can simply apply the appropriate provisions for each structure.

However, this begs a question - how on earth are you justifying the two-stage analysis for a steel moment frame podium with wood on top? I can't fathom economically achieving the 10x stiffness requirement.