Seismic Response Spectrum, Fa & Fv values and their effect
Seismic Response Spectrum, Fa & Fv values and their effect
(OP)
Hi,
I'm producing a seismic hazard spectrum for a water tank and came across something that I'm having trouble figuring out. I originally ran a spectrum analysis with the USGS Earthquake Ground Motions Parameters program using a Site Class D and was asked to change the soils definition to Site Class E. The Site Class D spectrum has a higher seismic acceleration (Sa) than the Site Class E. After re-running the site using all of the definitions (A-E) I observed that the Sa values were highest to lowest in this order D, B/C (approx. the same), E, and finally A.
I thought that the Sa values would drop from A to E, but this wasn't the case. So, my question is... why? The Fa factor appears to be the dominant variable, but the effect of the site class seems slightly contradictory. I've tried to find literature on why this is, but to no avail.
Can anyone point me in the direction of a reasonably simplified description of how and why the Fa and Fv values were chosen for their site classes?
Thanks for any help!
I'm producing a seismic hazard spectrum for a water tank and came across something that I'm having trouble figuring out. I originally ran a spectrum analysis with the USGS Earthquake Ground Motions Parameters program using a Site Class D and was asked to change the soils definition to Site Class E. The Site Class D spectrum has a higher seismic acceleration (Sa) than the Site Class E. After re-running the site using all of the definitions (A-E) I observed that the Sa values were highest to lowest in this order D, B/C (approx. the same), E, and finally A.
I thought that the Sa values would drop from A to E, but this wasn't the case. So, my question is... why? The Fa factor appears to be the dominant variable, but the effect of the site class seems slightly contradictory. I've tried to find literature on why this is, but to no avail.
Can anyone point me in the direction of a reasonably simplified description of how and why the Fa and Fv values were chosen for their site classes?
Thanks for any help!





RE: Seismic Response Spectrum, Fa & Fv values and their effect
Google NEHRP commentary to obtain a complete discussion.
RE: Seismic Response Spectrum, Fa & Fv values and their effect
RE: Seismic Response Spectrum, Fa & Fv values and their effect
here's some educational materials. see fema 451b
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