mixed seismic site class

[nbr1]

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.

 

[jdgengineer]

See Chapter 20 of ASCE 7-05.

 

[nbr1]

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.

 

[moe333]

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