Sp coefficient in seismic design

[Roohol]

dear all
in seismic calculation of API 650, can we assume that sp is equal to seismic zone factor?
for example if zone factor is 4 in a site, then Sp is equal to 0.4 or not?
how can estimate Sp if we dont have exact site condition?

 

[heman65]

Actually I would like to know this too!! Anybody?

 

[IFRs]

The 1997 UBC said: Zone 0 = 0.0g. Zone 1 = 0.075g. Zone 2A = 0.15g. Zone 2B = 0.20g. Zone 3 = 0.30g. Zone 4 = 0.40g.

If I remember correctly, the values on a seismic-risk map are figured this way: If you live in seismic zone 4, you have a one in ten chance that an earthquake with an active peak acceleration level of 0.04g (4/10 the acceleration of gravity) will occur within the next fifty years. Likewise, if you live in zone 1, you have a one in ten chance that an earthquake with an active peak acceleration level of 0.1g (1/10 the acceleration of gravity) will occur within the next fifty years.

It should be noted that due to the complex conditions affecting PGA, earthquakes of similar magnitude can offer disparate results, with many moderate magnitude earthquakes generating significantly larger PGA values than larger magnitude quakes.

 

[Roohol]

Thank you IFRs;
According to ASCE7-10, I need S1 and Ss for seismic calculation of pressure vessels and storage tanks.
I have these two parameters based on Sp (S1=1.25 Sp, Ss=2.5 Sp).
According to your reply I have found that Sp= 0.4 for zone 4 , Sp=0.3 for zone 3,... . Is it correct?
Please clarify.
Thanks a lot.
Roohol

 

[IFRs]

I would be leery of using such an Sp without good technical backup. The internet is not "good technical backup". What country / area are you working in?