Seismic Design Category

[wallerdf]

I have a 1 story wood framed building. I have calculated SDs and SD1.

SDs is .260 which is in SDC B.
SD1 is .137 which is barely in SDC C.

I'm trying to use the alternate determination of IBC 1613.5.6.1 to use SDs alone to determine my SDC. #1 I have figured my approximate period based on ASCE 12.8.2.1 and it is less than .8Ta. I'm getting hung up on #2. I can't find where the fundamental period enters into the drift equation. I'm looking at the NDS for the deflection equation of a shear and don't see it. I meet the requirements of #3 and #4.

I see in ASCE they say to use the seismic design forces based on the computed fundamental period when determining the drift (12.8.6.2). The period has an affect on the maximum Cs which is in the seimic base shear calculation. Is that what they are refering to.

It just seems to me that #1 and #2 are basically the same.

Any help understanding would be appreciated.

 

[DST148]

Seismic Drift calculations - For strength design of members the code imposes an upper limit on the time period to be used for evaluating the base shear. For drift calculations there is no such limit. You may have to perform another analysis for base shear using the computed fundamental period of the structure and check story drift limits.