Site Class F Fa & Fv values 1

[WARose]

ASCE 7-10 kicks you into doing a site specific survey to (essentially) obtain Fa & Fv values for site class F (see section 11.4.7)

Question for anyone who has had this done: you come out of this essentially with your Sds.....but have you gone back and calculated the equivalent value if you had just used Table 11.4-1 & 11.4-2 (p.66)? In other words: what sort of values of Fa & Fv did this give you? Naturally it will vary from site to site.....but I am just looking for ballpark numbers here.

Thanks.

 

[WARose]

Anybody? Thinking about this during the weekend.....I would think the maximum site magnification factor would be on the order of 5-10. But that is with a guess at damping (using 5% as a minimum). And with real crappy soil.....I'm not 100% sure about that.

 

[WARose]

Researching further this week.....I'm really second guessing running with a maximum site magnification factor of 5-10. Looking at the data, even with some pretty high shear strains in the soil (that you would expect in a seismic event).....the damping in many cases is still less than 5% for some pretty competent soils.

I'm just going to assume something outrageously conservative for the time being and hope testing backs me up when the time comes.

 

[Wallache]

To answer your initial post, on my recent project with Site Class F, the Fa and Fv values came out to roughly that of Site Class D. This was for a site with decent soils but had a liquefiable layer approximately 50' down.

 

[WARose]

Thanks Wallache.