ASCE 7-10 Site Class F

[SteelPE]

I recently turned down a project that I was exactly sure how to solve. The project would have required me to design a pile foundation system for a metal building. I was given the architectural drawings and the soils report to look at prior to turning down the project.

One particular issue contained within the soils report was the soils classification. The report listed the site class as a F. My question is in regards to this classification, who is responsible for determining the MCE’s for this soil? Is that the responsibility of the geotechnical engineer or the structural engineer?

 

[Okiryu]

For site class F, the project will require to to do a site-specific seismic analysis to get the response spectrum. I work in geotech and this task is normally given to us which I think is good because the site-specific seismic analysis involves geotechnical site investigations (Vs measurements) and soil analysis.

 

[SteelPE]

Okiryu,

That is interesting. I was given a full geotechnical report and they attempted to calculate Sds and Sd1 but just stated that they couldn't be calculated. After some thought I figured they either A) didn't know how to do it or B) didn't care to do it. It seemed like something that was over my head, and was a small part of why I declined the project (I didn't want to be part of the finger pointing).

 

[Okiryu]

SteelPE, ASCE 7 indicates clearly that a site-specific response analysis is required for site class F. The Geotech should have written that in the report and try to get some funds to perform the analysis later. There is also an exception - site-specific response analysis is not required if the building has a period of less than 0.5 sec.