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RE: ASD Wind - Stress Increase

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There was an article titled "The Mysterious 1/3 Stress Increase" in the AISC
Engineering Journal, 4th Quarter, 1977. It discusses various hypotheses as
to the basis for the 1/3 increase, but it notes that the earliest uses do
not seem to define its original basis. However, the article does conclude
that the "short duration" aspect seems to be the most common assertion as to
why it is permitted. It quotes McCormac's "Structural Steel Design" textbook
and the "Building and Construction Handbook" (F.Merritt, Chapter 6 by H.
Stetina) as supporting the argument that it is allowed because of the "short
duration" of the peak wind force. Other arguments suggest that it is due to
the unlikely occurrence of maximum wind with the full value of other live
loads. 

Nevertheless, this article argues that if the 1/3 increase is due to load
duration, it should no longer be applicable due to current wind design
methods which include "gust factors" to account for duration. 


William C. Sherman, PE
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com


> -----Original Message-----
> From: Tim Campbell [mailto:tcampbell(--nospam--at)chcstructural.com]
> Sent: Sunday, February 23, 2003 5:21 PM
> To: seaint(--nospam--at)seaint.org
> Subject: ASD Wind - Stress Increase
> 
> 
> List,
> 
> Does anyone know of any steel literature stating that the 1/3 increase
> in allowable stress in the ASD manual for load combinations 
> that include
> wind is due to load duration?  TIA
> 
> Tim
> 
> Timothy R. Campbell, P.E.
> tcampbell(--nospam--at)chcstructural.com
> 
> 
> 
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