2009 IBC 1605.3.1 Exception (2)

[JoshH726]

ASCE 7-05 load combination 2.4.1(6) includes the effects of both E and Lr or S. Given that 2.4.1(6) includes E, you are bounced to Section 12.4.2.3 to use a modifed equation of 2.4.1(6), 12.4.2.3(6) in this case, which is (1.0 + 0.105*SDS)*D + H + F + 0.525*rho*QE + 0.75*L + 0.75*(Lr or S or R).

Now reading 2009 IBC 1605.3.1 Exception (2) - "Flat roof snow loads of 30 psf or less and roof live loads of 30 psf or less need not be combined with seismic loads. Where flat roof snow loads exceed 30 psf, 20 percent shall be combined with seismic loads".

So does this mean that ASCE 7 12.4.2.3(6) becomes (1.0 + 0.105*SDS)*D + H + F + 0.525*rho*QE + 0.75*L ?

 

[msquared48]

What they are talking about is whether or not you include a portion of the snow load as a portion of the dead load of the structure that will have the effect of increasing your seismic force. So, you are just increasing the "D" with the extra 20% of the snow that is required.

Mike McCann
MMC Engineering