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Re: Spectral Acceleration using 2006 IBC

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The seismic design accelerations under the IBC 2006 are based on a "Maximum Considered Earthquake" with a mean recurrence interval of 2,500 years (2% in 50 years). The code then has you reduce the load to 2/3 of that value for the design basis loads which approximates a 500 year mean recurrence interval (10% in 50 years). In California near major faults, however, you need to be careful because the 500 year events can approach the deterministically limited motion on a given fault. But I guess we don't have to worry about that until 1-1-08 when the IBC2006, as amended, becomes the California Building Code.
Bill Cain, SE
Berkeley CA

-----Original Message-----
From: Larry Hauer <lrhauer(--nospam--at)>
To: seaint(--nospam--at)
Sent: Fri, 13 Jul 2007 3:03 pm
Subject: Spectral Acceleration using 2006 IBC

To get the long and short spectral accelerations for designing earthquake forces I have gone to the USGS website with the required latitude and longitude. However, the website lists 2 values for each, a 10%PE in 50 yrs. and a 2%PE in 50 years. Which of these sets of values am I to use when designing to the 2006 IBC? 
Thanks in Advance, 
Larry Hauer S.E. 
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