haynewp
Structural
- Dec 13, 2000
- 2,327
The special seismic combination is to be "delete without substitution" according to the 2007 IBC supplement on page 119:
The section seemed a little strange to me anyway, it reads as if you are supposed to apply the same 2 combinations whether you are using allowable stress or strength design and doesn't mention a reduction for allowable stress (as if the 1.2D applies either way):
1.2D+ f1L +Em (Equation 16-22)
0.9D+Em (Equation 16-23)
The way ASCE has it makes sense (section 12.4.3.2), even though they don't call them "special seismic combinations" they reduce the combinations for allowable design. I am not sure why it was removed in the 2007 IBC supplement without any mention of what should replace it. Are we supposed to just use ASCE's version of the combinations with "Em" now?
The section seemed a little strange to me anyway, it reads as if you are supposed to apply the same 2 combinations whether you are using allowable stress or strength design and doesn't mention a reduction for allowable stress (as if the 1.2D applies either way):
1.2D+ f1L +Em (Equation 16-22)
0.9D+Em (Equation 16-23)
The way ASCE has it makes sense (section 12.4.3.2), even though they don't call them "special seismic combinations" they reduce the combinations for allowable design. I am not sure why it was removed in the 2007 IBC supplement without any mention of what should replace it. Are we supposed to just use ASCE's version of the combinations with "Em" now?
