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mixed seismic site class

mixed seismic site class

mixed seismic site class

Does anyone have any experience with sites which are justified with the assignement of several site class designations....(A through F as noted in IBC Table 1613.5.2). Say you have a site with N-values or other that would support both a Site Class C and a Site Class D.

Specifically, I am interested to know if it is justifiable to average the Fa and Fv values from each site class; and use this average result as the basis for determining SDs and SD1.

Intuitively, I would think taking the most conservative site class designation would be okay; however, I would think it would also be more costly in all situations.

RE: mixed seismic site class

See Chapter 20 of ASCE 7-05.

RE: mixed seismic site class

ASCE 7-05, Chapter 20 does not address the condition where you may two 'justifiable' site class conditions under one building area.

I was curious if adjusting/averaging the Fa and Fv values for the two site class conditions that were ascertained was justifiable.

Say for example you had very shallow rock under 1/2 of the building, then deep under the remainder.

RE: mixed seismic site class

You need to use the more conservative values. I would not use an average.

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