Seismic Base Shear and load combinations
Seismic Base Shear and load combinations
(OP)
I am using the Equivalent lateral force procedure for my seismic loads. I calculate V (seismic base shear) per 12.8.1. I then want to look at my diaphragm, chords, etc. and design them accordingly. Section 12.10 gives a min and max of forces for this condition. First question: do I compare the V value with the max and min given in 12.10 and use the larger of V and Fpx max? Or just use Fpx max? Second question, before designing my members and connections, I would assume I would take the seismic base shear V and use this value in the load combinations in section12.4.2.3 (I'm using allowable stress design). Does my V then become my Qe? I would think so from section 12.4.2.1 and the definition given for Qe. Just want to make sure I am okay in using the 0.7 factor on my V. And to check if my Fpx max (from 12.10.1.1) is smaller than my V from 12.8.1, I still need to use V. Thanks and have a great day.






RE: Seismic Base Shear and load combinations
1) Determine V, accounting for min/max provisions. Stick with this V in everything that follows.
1) Use your V to get your Fp story shear values at each floor. These values are used for the design of your vertical lateral load resisting system.
2) Use the Fp values to get your Fpx diaphragm shear values at every floor. These are normally higher than the story shear values.
3) Compare Fpx to Fpx min/max and use the value that governs for your diaphragm and chord design. At this stage, you no longer care about V or Fp in your load combinations. Your seismic load is just Fpx.
This is the general procedure for buildings with any number of stories. For a single story buildings, V = Fp by mathematical definition.
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