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RE: ASCE 7-98 Vs. ASCE 7-95 (Wind Provisions)

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-----Original Message-----
From: Brian M. McMahon [mailto:brian(--nospam--at)ubsdesign.com]
Sent: Wednesday, May 30, 2001 11:04 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: ASCE 7-98 Vs. ASCE 7-95 (Wind Provisions)

ASCE 7 comparisons for wind provisions (general):
 
ASCE 7-95 is a big increase from ASCE 7-93 (wind velocities increased and decreased coefficients).
 
ASCE 7-98 is a happy median for most people between ASCE 7-93 and ASCE 7-95 (wind velocities reduced and the coefficients increased).
 
Brian, my recollection from having taken the ASCE short course on ASCE 7-95 back about four years ago (Kishor Mehta taught the seminar) was that there really was NOT an appreciable change in wind force calculated by ASCE 7-93 at a given location, but rather the whole thing was "scaled" to be able to use basic wind speeds based on three-second gust, since records are now and have been for some years, kept using that method.
 
I even remember Dr. Mehta going through an example calculation (I think assuming Galveston Island, TX as the location) using both 93 and 95, to demonstrate this.
 
Now, the basic wind speeds WERE changed somewhat in certain locations, because the wind speed map in 7-95 reflected a computer model of as many measurable storms as the researchers could get their hands on, so at a given location there may HAVE been a change upward. But in general the two methods were supposed to yield comparable results.

William L. Polhemus, Jr., P.E.
Polhemus Engineering Company
Katy, Texas
Phone 281-492-2251
Fax 281-492-8203