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RE: Earthquake force considered in load combination (IBC2000)

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Title: RE: Earthquake force considered in load combination (IBC2000)

        E should be calculated using the full dead weight and possibly a percentage of the live load or snow load as well. I am not an expert on the codes, but I believe Equation 16-11 is essentially a load combination for overturning or uplift. Instead of calculating a factor of safety for overturning, you make sure that the building stays in equilibrium if this equation is used. BOCA used to have a note that said that no more than 2/3 (.67) of the dead load could be used to resist uplift or overturning. IBC just turned that statement into an equation and made it a little more conservative in the process. I think that the code writers want to be sure that engineers don't use a factor of safety for overturning, etc. less than 1.667 (1/.6). Also, when you calculate E the vertical portion (.2*SDS*D) of the seismic force should be opposing gravity loads.

Wesley C. Werner, EIT