Friday, November 11, 2011

RE: SDS Value

I think the min, max, and centroid values are presented when you do a lookup based on zipcode.  In my neck of the woods, there isn't usually enough difference between the min/max, so I just use the centroid (average) value.
I suggest a Lat/Long lookup for your specific site.

Jeremy South, PE
Jenkins Engineering Inc.


From: []
Sent: Friday, November 11, 2011 2:31 PM
Subject: Re: SDS Value


Not really sure what you mean.  When using the USGS program you start at the top and pick International Building Code then Conterminous 48 states, if not in Hawaii or Alaska, then enter the latitude and longitude and all the numbers come out and then you can adjust for soil site class.  Where do you see the minimum, maximum, centroid values?  If you are using the site spectrum then you would enter with your structures period and pull off the corresponding acceleration.

Thomas Hunt, S.E.

From:        "Thomas Kennedy, P.E." <>
To:        <>
Date:        11/11/2011 11:47 AM
Subject:        SDS Value

I am doing a seismic retrofit on a CMU building in Los Angeles. The owner is
in the process of selling the property and the buyer is hiring another
engineer to review the retrofit plans. When determining the Seismic
Coefficients from the USGS's software, the company I work for has always
used centroid value for the SDS (Not the Maximum or minimum). Does anyone
know anywhere in the 2011 LABC or 2010 CBC or ASCE code where it states if
you are required to use the centroid value, the maximum value or the minimum


Thomas Kennedy, P.E.

Erstad Engineering, Inc.
3463 Oceanview Blvd
Glendale CA 91208
PH:  818-249-8400
Fax: 818-249-8405

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