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RE: Exposure D Wind

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I have no more proficiency in wind than any other topic I take a crack at,
but this is my take on it.

The UBC had a very distant relationship regarding wind and the ASCE 7 wind
provisions development.  BOCA and SBC were much more directly involved in
the ASCE 7 wind provisions.  When the IBC effort started it was clear that
the ASCE 7 wind provision development effort would be the focus for wind
provisions for the IBC.  ASCE 7 converted over to a "3 second gust" wind in
1995.  UBC did not follow suit, and stayed with the "fastest mile" wind.
But now that the codes are one big happy family, the wind provisions will be
fathered in the ASCE 7 process, thus the conversion to the "3 second gust"
wind.  

The fastest mile wind now accompanies steel ASD, concrete working stress,
and seismic zones in the code trash heap.

The origin for the 2000 IBC wind provisions is the ASCE 7-98.  The changes
in exposure category are discussed in the commentary, and came from some
research by Vickery and Skerlj, "On the Elimination of Exposure D along the
Hurricane Coastline in ASCE-7", Report for Andersen Corporation by Applied
Research Associates, ARA Project 4667, March 1998.  Peter Vickery served on
the ASCE 7-98 Task Committee on Wind Loads.

What is interesting is when you actually bust the numbers, some structures
and elements go up for wind forces and some will actually go down.  

Regards,
Harold Sprague


> -----Original Message-----
> From:	Tom.Hunt(--nospam--at)d-fd.com [SMTP:Tom.Hunt(--nospam--at)d-fd.com]
> Sent:	Wednesday, June 07, 2000 8:52 AM
> To:	SEAINT(--nospam--at)seaint.org
> Subject:	Exposure D Wind
> 
> Any wind guys or gals out there??
> 
> I just noticed that the 2000 IBC specifically includes Exposure D wind
> category to the West Coast.  The 1997 UBC specifically excludes Exposure D
> for areas with basic wind speeds less than 80 mph (fastest mile) which
> includes central and southern California.  Does anyone know the background
> to this?  Looks like all structures 1500 feet from the Pacific Coast will
> need to be designed for higher wind loads.
> 
> Thomas Hunt
> Duke/Fluor Daniel
> 
>