# RE: Seismic Recurrance Intervals

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Seismic Recurrance Intervals
• From: "Abdul Chahim" <chahim(--nospam--at)abam.com>
• Date: Wed, 5 Jul 2000 12:38:42 -0700
• Delivered-to: fixup-seaint(--nospam--at)seaint.org@fixme
```Try FEMA 273 section 2.6.1.3?

> -----Original Message-----
> From: Ritter, Mike [mailto:mritter(--nospam--at)lgt.lg.com]
> Sent: Wednesday, July 05, 2000 11:36 AM
> To: SEAOC List Server (E-mail)
> Subject: Seismic Recurrance Intervals
>
>
> Friends,
>
> Another seismic question for the group.
>
> I'm currently using the 2000 IBC on a project, which utilizes the
> Maximum Considered Earthquake (MCE) maps.  No problem.  I can follow the
> methodology fine.  However, I have project criteria that states I'm
> supposed to be using earthquake demand based on a 1000 year recurrance
> interval earthquake (or, I think, a 5% probability of exceedance in 50
> years).  Most codes have seismic demand based on 10% probability of
> exceedance in 50 years (or about 500 years).  I could not find anything
> listed like that for 2000 IBC, so I pulled out my FEMA 310 which uses
> the same (new) maps.  I found MCE defined as "2% probability of
> exceedance in 50 years...".  That, I think, goes with a 2500 year
> earthquake.  So.  How do I get to the 1000 year earthquake?
>
> I understand the 2/3 factor in 2000 IBC (to get Sds and Sd1) does
> something to take into account an approximate 50% reserve capacity in a
> typical code designed structure (i.e., Sds = Sms x 2/3 or Sds = Sms/1.5)
> but I'm not sure if it really reduces the recurrance interval.  If it
> does, what does it go to?  1000 years?  500 years?
>
> Any help would be appreciated.
>
> Thanks in advance,  Mike
>
> Michael D. Ritter, PE
> Senior Structural Engineer
> Lockwood Greene Technologies
> 1201 Oak Ridge Turnpike
> Oak Ridge, TN  37831
> (865) 220-4418
> (865) 220-4310 (fax)
>
>
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