Hello Dear Richard, I´m from Venezuela and I have worked a lot in designing tanks.
The most difficult part when I´m dealing with clients is that sometimes they want to use the ASCE code and the API-650 appex E to do the seismic analysis.
In Venezuela we have our standard to evaluate the seismic load in the tanks, and from my point of view ,that standard, is one of the most clear and complete standard about seismic.
I have read several seismics standard but I always end up in the same point, the Famous table E-1 and E-2.
As the API and ASCE standard define for the non ASCE zones, engineers can use the Sp value, and then, making some sustitution the will have the So and S1. BUT when you use both table you have to "match" those values (s0 and S1) with some soil condition to get Fa and Fv.
HERE is the big problem , It is very difficult to make that match and the worst part , FROM MY POINT OF VIEW, is that Engineers Try to "model" the soil response or the Spectral response just with the valu of Sp.
I think that using this method or this approach would raise some mistakes or will give a non appropiate model of response...
I would like know you opinion about it.
BEst Regards.
JM