huangyhg

seismic loads for wood structure on steel frame
well, here's my situation:
i have a five story building. the upper three levels are to be wood framed w/ plywood shearwalls and the lower two levels are to be steel x-braced frames with concrete slab diaphragms.
my question is in determining seismic loads, would i look at the three story wood framed portion separately (with and r value of 6.5), then add these loads to the two-story steel frame structure and add the lower level loads with an appropriate r factor for the steel frames?
any opinions?
thanks
ice
check out our whitepaper library.
per asce 7 12.2.3.1,
"r,cd and ^o for vertical combinations"
"the value of the response modification coefficient, r, used for design at any story shall not exceed the lowest value of r that is used in the same direction at any story above that story. likewise the deflection amplification factor, cd, ... over strength factor, ^o, ... shall not be less than largest value at any story above..."
so, in short, yes. design the three upper floors with the appropriate r, then apply those loads to the lower two floors using the r=3.25 (i'm guessing) for those analyses.

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