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Re:Foundation bearing pressure per 1997 UBC

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William,

That's correct for native (not fill) sands, with an embedment of 6 feet and a
width of 6 feet, for combined dead+live+dynamic (seismic and wind) loads, you
can use 6,000 psf, according to the UBC.  You can increase the allowable bearing
pressure by 20% for each additional foot of embedment and/or width beyond one
foot.

Just a friendly question:  Does your E&O Insurance cover geotechnical
consulting?

Tom Benson at Lowney Associates
1785 Locust Street, Suite 10
Pasadena, CA 91106-1614
(626) 396-1490
FAX: (626) 396-1491
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____________________Reply Separator____________________
Subject:    Foundation bearing pressure per 1997 UBC 
Author: <seaint(--nospam--at)seaint.org>
Date:       9/26/2000 12:47 PM

I was looking at the 1997 UBC for prescriptive bearing pressures when
specific soil's test data is not available. Table 18-I-A shows a 1500 psf
allowable bearing pressure for sand, which seems reasonably conservative.
But then I looked at footnote 2 and saw that this is based on a 12-inch wide
and 12-inch deep footing and the allowable bearing pressure can be increased
up to 3 times the tabulated value for deeper and wider footings. Also a
one-third increase can be taken for wind load design. Using these
provisions, the allowable bearing pressure becomes 1500 X 3 X 1.33 = 6000
psf. This seems excessively high to use without specific soil's test data
but the code seems to allow it. Am I missing something here??


William C. Sherman
Camp Dresser & McKee, Inc.
Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com


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