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RE: Spectral acc. coeffs. in IBC2003

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My understanding is that the USGS maps are solely "probabilistic maps",
whereas the NEHRP/IBC maps made adjustments in California based on
"deterministic" methods for known faults. The adjustments in California
reduced the values relative to the USGS maps. 

William C. Sherman, PE 
(Bill Sherman) 
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com
 

> -----Original Message-----
> From: Will H [mailto:haynewp(--nospam--at)hotmail.com] 
> Sent: Thursday, November 11, 2004 5:15 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Spectral acc. coeffs. in IBC2003
> 
> Why would the values here be different than the software?
> 
> http://eqint.cr.usgs.gov/eq/html/zipcode.html
> 
> Looks like Ss=2.09 and S1=0.77 for 90012?
> 
> Will Haynes, P.E.
> 
> >From: "Aswin Rangaswamy" <aswinpe(--nospam--at)hotmail.com>
> >Reply-To: <seaint(--nospam--at)seaint.org>
> >To: <seaint(--nospam--at)seaint.org>
> >Subject: Re: Spectral acc. coeffs. in IBC2003
> >Date: Thu, 11 Nov 2004 14:47:47 -0800
> >
> >The maps in the IBC are just to make the book pretty.  I dont think 
> >anybody actually uses them.  Values are obtained by punching 
> in the zip 
> >code or the latitude/longitude information into a software program.  
> >The program contains the information on the maps.  Los 
> Angeles is quite 
> >wide and the values can differ.  Based on the downtown LA 
> zip code of 
> >90012, I get a Ss=1.5, S1=0.6.  Palmdale (about 45 miles 
> from downtown) 
> >which is over the San Andreas Fault has a Ss=1.597, S1=0.883.
> >
> >Hope this helps.
> >
> >- Aswin
> >--------------------------------------------
> >Aswin Rangswamy, P.E.
> >Los Angeles, California
> >-------------------------------------------
> >
> >----- Original Message -----
> >From: "BHASKAR BONGARALA" <bhaskar_civil(--nospam--at)iitb.ac.in>
> >To: <seaint(--nospam--at)seaint.org>
> >Sent: Thursday, November 11, 2004 9:18 AM
> >Subject: Spectral acc. coeffs. in IBC2003
> >
> > > Sir
> > > For a site(class-B) at Los Angeles,CA, the mapped Max. 
> considered Eq.
> > > spectral response accelaration at shortperiod(Ss) and at 1-sec. 
> >period(S1)
> > > are as follows from the figures given in IBC2003. Please 
> correct in 
> > > case of any mistake in the values below.
> > >
> > > SS = 1.9   => SMS = 1.9  => SDS = 1.267
> > > S1 = 0.75  => SM1 = 0.75 => SD1 = 0.5
> > >
> > > Bhaskar

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