seismic story drift - stability coefficient

[peal724]

from ASCE7, the stability coefficient theta has a Px defined as "the total vertical design load at and above Level x; where computing Px, no individual load factor need exceed 1.0."

so, let's say I'm checking a roof only with enough snow that 20% has to be used in the effective seismic weight and I'm using ASD load combos for my building. what is the "total vertical design load" in terms of dead, roof live, snow, etc?

I guess I'm having trouble understanding if this is supposed to be

D+S
D+0.2S
D+0.75S+0.525E

Any thoughts, suggestions?

 

[JoshPlumSE]

If you're using ASD design, you can ignore that portion of the code. It's basically just saying that you can use ASD level vertical loads to calculate the stability coefficient even when you are doing LRFD design.

Personally, I ignore that and just use the LRFD loads. After all, the other codes (AISC, ACI, et cetera) do not allow this liberalization. In fact, the AISC guys tell you that you have to calculate your stability effects at LRFD level loads even when you are using ASD design! So, there is some direct code contradiction here.