Site Response Analysis for Site Class F - Catch-22?

[Timbanjo]

Hi All,
I have done a shear wave study of a site that gives a 1-D profile with V100 that puts it in site class D. However, there is a layer of organic material in one boring that would put the site automatically in class F, and require a site response analysis. So, in the site response analysis, I need to use a Shear wave velocity profile (got it...see above), but it is a class D profile. Question - can I do a probabilistic analysis (e.g. USGS data), or do I need to do a specific one (e.g. SHAKE)? If I do SHAKE, the input Vs profile (as measured on the site) will be a class D profile, so why can I not just do a probabilistic analysis assuming class D? A bit of a logic loop...or am I missing something.
Thanks for any advice.
Tim

 

[moe333]

I assume you are working in accordance with IBC 2009? You should generally be able to do the probabilistic option of the site specific analysis as outlined in ASCE 7-05 (if these codes are applicible to your project). Some projects require the determinsitic analysis (SHAKE, etc.) and I believe the criteria for using deterministic vs. prob. is discussed in ASCE 7-05. You would use the site specific SWV you obtained in the attenuation relationships for the probabilistic analysis. There is an outlined procedure for the analysis in ASCE 7-05.