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Re: Wind force -- codes, building design, officials, etc.

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Gary, 

It's GREAT to know that *someone* who is (at least partly) responsible for the present debacle is participating in this round of, ahem, venting! 

This is from someone in the trenches who would be *glad* to have a conservative fallback position on wind loads for single-family residence in earthquake country, where seismic often governs, to avoid having to spend days on what amounts to a meaningless wind calculation exercise. 

I definitely agree with the writer who said (something like) that critical, unusual, etc., structures should have more detailed provisions available, so that their designer can "sharpen his/her pencil."  But for the vast majority of us for whom wind design is often a purely academic exercise, in many instances, we would like to have a very simple, conservative approach as an option.

Thank you for your participation in this list, and in the committee you mentioned.

And for the writer in Oz, whose name escapes me at the moment, I think you must have more flexible, AKA reasonable, building officials than some I've encountered.  You make it sound like a discussion between professionals, rather than a dude in the trenches just trying to get a reasonable, but perhaps imperfect, structural design through the permit process. 

Sincerely,

Ralph Hueston Kratz, S.E.
Structural Engineer
Richmond CA USA

In a message dated 12/19/08 10:33:26 AM, gehrlich(--nospam--at)nahb.com 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
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
gehrlich(--nospam--at)nahb.com
Attend the 2009 International Builders' Show
January 20-23, 2009, Las Vegas, NV
www.BuildersShow.com

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


 
Waaaay back when sanity prevailed.
 
 
T. William (Bill) Allen, S.E.
ALLEN DESIGNS
Consulting Structural Engineers
 V (949) 248-8588 • F(949) 209-2509

-----Original Message-----
From: HBAP(--nospam--at)aol.com [mailto:HBAP(--nospam--at)aol.com]
Sent: Thursday, December 18, 2008 2:07 PM
To: seaint(--nospam--at)seaint.org
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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