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RE: Seismic Base Shear

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Ss and S1 are spectral responses  for a site class B [rock] MCE [maximum
considered earthquake] with 5% damping.  Ss and S1 are derived for a 2475
return period earthquake [2% probability of exceedence in 50 years].  Ss and
S1 are modified by Fa and Fv for other soil types [Sms=Ss*Fa and Sm1=S1*Fv].

Sds and Sd1 are for 475 return period earthquakes [10% probability of
exceedence in 50 years] and are used for design [Sds=2/3*Sms and
Sd1=2/3*Sm1].

In the 1997 UBC the EPA was Ca and that was multiplied by a 2.5 fault
amplification factor to get a spectral pseudo acceleration.  The EPA is
built into S1 and Ss IBC spectral values.  

Scott M Haan P.E.
Plan Review Engineer
Building Safety Division http://www.muni.org/building
Development Services Department
Municipality of Anchorage
phone:907-343-8183  fax:907-249-7399
mailto:haansm(--nospam--at)ci.anchorage.ak.us



-----Original Message-----
From: Sunho Shim [mailto:sunho.shim(--nospam--at)som.com]
Sent: Tuesday, May 01, 2001 7:58 AM
To: seaint(--nospam--at)seaint.org
Subject: Seismic Base Shear


Hello, Engineers


I am comparing seismic base shear for several codes.
UBC and ASCE seem to use Effective Peak Acceleration and Effective 
Velocity-Related Acceleration.
However NEHRP 97 AND IBC200 are using Spectral Acceleration at short period 
and 1 second.

How can I convert EPA,EPV to Ss, S1?




Thank you for your answer.

Sunho Shim


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