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Re: Wind forces

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That beckons the question from all California Engineers why don't we use these values for structures under 40, 50, or 60 feet( pick a number)  in height . Why do we have to go through the gyrations of ASCE 7.
Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA
In a message dated 12/19/2008 10:33:19 A.M. Pacific Standard Time, gehrlich(--nospam--at) writes:

I hate to throw water on everyone, but I wouldn’t necessarily call the old uniform loads “sanity”. We’re debating in the ASCE wind committee right now backing off some on the current minimum load, which is 10psf. The problem is that on a typical low-rise (~35’ mean roof height) gable roof structure, it takes something like a 150mph wind (if I recall correctly) to generate a 10psf load on the vertical projection of the roof using the analytical provisions. And the wind ends up governing over SDC C, and even SDC D level seismic forces.


This explains why all those buildings designed for 15psf, 20psf, or 25psf uniform wind loads don’t seem to have any problems—it would take a Cat 5 or an EF4 to take them down. Regardless of whether they’re built anywhere that could get a wind event of that magnitude.



Gary J. Ehrlich, PE
Program Manager, Structural Codes & Standards
National Association of Home Builders (NAHB)
1201 15th Street, NW, Washington, DC 20005
ph: 202-266-8545  or 800-368-5242 x8545
fax: 202-266-8369

Attend the 2009 International Builders' Show
January 20-23, 2009, Las Vegas, NV


From: Bill Allen [mailto:t.w.allen(--nospam--at)]
Sent: Thursday, December 18, 2008 6:05 PM
To: seaint(--nospam--at)
Subject: RE: Wind forces


Waaaay back when sanity prevailed.



T. William (Bill) Allen, S.E.


Consulting Structural Engineers
V (949) 248-8588 F(949) 209-2509

-----Original Message-----
From: HBAP(--nospam--at) [mailto:HBAP(--nospam--at)]
Sent: Thursday, December 18, 2008 2:07 PM
To: seaint(--nospam--at)
Subject: Wind forces


Ahhh, for the good ol' days!


From the UBC 1949:


Sec. 2307 (b):  For purposes of design the wind pressure shall be taken upon the gross area of the vertical projection of buildings and structures at not less than 15 psf for those portions of the building less than sixty feet (60') above ground . . . ".


Hugh Brooks, SE


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