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Cs Calcualtion

Cs Calcualtion

Cs Calcualtion

(OP)
In most of the structures I design, I have always had a hard time with the seismic loads. I always end up with very large loads. Today I was going through a structure that another engineering firm designed on a site where I also did a building and I decided to compare notes. To my surprise, their Cs is much much lower than the one I used. Now, there are a few differences in the structures but I was amazed at how low their value was.

I have attached a snapshot of their seismic criteria from their note sheet. I am wondering how they ended up with a Cs of 0.027 in this structure. The only item I don't know is the period they used for the structure (which isn't required to be given by the code). The structure is two stories with top of roof for this building is 33'-6" with an equipment platform at 48'-6". In order to use a Cs this low your period would need to be 0.901. Does the Cs seem right to others?

RE: Cs Calcualtion

Perhaps the 0.027 value is a typo. Using the parameters provided and ASCE 7-05, I get Cs = 0.067.

RE: Cs Calcualtion

(OP)
Didn't think about a typo. 4500 kips for a two story structure weight does seem large. I would try to calculate it myself but the structural drawings do not have dimensions on them and there are 25 tightly spaced grids in one direction and 16 in the other direction. If the value was 0.067 then the structure weight would be about 1800 kips.

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