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RE: Seismic Zone 0 vs IBC

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Yes, seismic will now have to be considered where it was not previously
considered, when designing in accordance with the IBC. 

In the IBC, there is no such thing as "Zone 0" or a zone without any seismic
design ground motion. And according to IBC 1603.1.5, item 5, the seismic
design base shear must be reported on the construction documents regardless
of whether seismic loads govern the lateral design - so the seismic
calculations must be performed even if wind controls. 

For a project I did in Fort Worth, Texas, which started out under the 1997
UBC in seismic Zone 0 but was completed under the 2000 IBC, I found that
seismic controlled over wind for some structures (concrete/masonry
structures). One thing that also became apparent is that sometimes seismic
overturning forces are more critical than wind loadings, even though seismic
base shear may be slightly less. This is due to the fact that much of the
seismic lateral force is at roof level for a single story structure, but the
centroid of the wind load is much lower than roof level. 

> -----Original Message-----
> From: Bill Polhemus [mailto:bill(--nospam--at)]
> Sent: Saturday, July 20, 2002 8:37 AM
> To: seaint(--nospam--at)
> Subject: RE: Steel Moment Frames in Seismic Zone 0
> Okay, dumb question time (I seem to be the one that brings 
> them up, so other
> people don't have to. C'mon, you know who you are!)
> Anyway, I haven't had time to catch up with the IBC as yet, 
> though I do have
> a copy sitting here looking pretty. I remember hearing that 
> seismic design
> is going to HAVE to be considered even in places were it 
> never was before
> (i.e. Zone 0/Zone 1). Is this true?
> It appears from Charlie's response to Mark that this is the 
> case. I know I
> could just crack open the UBC and start reading (and I've 
> even purchased
> several of the supplemental publications such as the 
> "Structural/Seismic
> Design Manual for IBC Vol. 1," so I could go there as well).
> But I like the capsule descriptions that folks like Charlie and Harold
> always give.
> Thanks.
> William L. Polhemus, Jr. P.E.
> Polhemus Engineering Company
> Katy, TX, USA
> Phone (281) 492-2251
> FAX (281) 492-8203
> email bill(--nospam--at) 

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