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Re: DC Spectral Ordinates

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Chapter 3 of TI-809-04 is pretty clear when it indicates that you 
should use the MCE maps.  You will notice that the "conversion 
algorithms" used to convert UBC zone to spectral ordinates appears in 
the section "Design values for sites outside the U.S." and warns that 
"the conversion is approximate."  The UBC zones lump a wide range of 
seismic hazard together.  The conversion had to be based on the 
largest values in the range.

Since your site is in the U.S., the MCE maps should be used.

------- Forwarded Message Follows -------
Date:          Wed, 24 Nov 1999 10:06:53 -0500
From:          "Nicole Stoudt" <NSTOUDT(--nospam--at)MBAKERCORP.COM>
To:            <seaint(--nospam--at)>
Subject:       DC Spectral Ordinates
Reply-to:      seaint(--nospam--at)

Please Help!

I am working on a seismic analysis in Washington DC.  The MCE maps
from FEMA-302 give me values of Ss =.14 and S1 = .07 for the site.

What confuses me is that TI-809-04 (which I must use) says that you 
can convert UBC Zones to S1 and Ss, and doing it the way they 
describe, I get Ss = .31 and S1= .14 for Zone 1. These two methods of 
getting the numbers are so different that I am not sure which to use, 
it seems to me the maps give the more realistic values, can somebody 
PLEASE help me? 

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Michael Valley                                   E-mail: mtv(--nospam--at)
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201