IBC 2003 Seismic Design Category

[sginal]

Section 1616.3 of IBC 2003 (it is also in IBC 2006) has an exception that allows you to determine your seismic design category based only on the short-period response acceleration (Table 1616.3(1)) if certain criteria are met. One of the criteria is that your seismic response coefficient, Cs must be calculated using an equation from ASCE 7. My question(s) is as follows. If using this exception allows you to be in design category A rather than a higher category, do you still need to use the equation from ASCE 7 to calculate Cs or can you use the minimum lateral force rocedure whereby Cs is equal to 0.01 (or 1%)?

 

[middletimer]

Good question. Several weeks ago I sent the same questions to ASCE and have not yet received a response. This will have a significant impact on certain building designs in the borderline seismic locations.

 

[UcfSE]

I would say you are using ASCE 7 within the IBC section 1616.3 to find if you can take exception. Once you get your information and find out if you qualify for the exception, you step out of the ASCE and back into the IBC with your now-found SDC, and proceed from there.

I would make double sure you calc'd everything right since it's a big change you're talking about. Note, this is all my opinion.