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RE: ASCE 7-98 Wind Provisions

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Note that a similar issue comes up in non-huricane areas.  If you look at
the definition of category D, the UBC excludes this category for all areas
with fastest mile wind speeds of less than or equal to 80 mph.  This would
apply to the entire cost of California.  However, ASCE-7 does not have this
exclusion so all structures within 1500 feet of the shoreline in California
will need to be designed for higher wind loads.  Since most of the talk has
been over IBC seismic issues I think everyone missed this.

Thomas Hunt, S.E.
Duke/Fluor Daniel

----- Forwarded by Tom Hunt/DFD on 03/19/01 07:25 AM -----
                    "T. Eric                                                                                       
                    Gillham PE"          To:     <seaint(--nospam--at)>                                               
                    <teric@gk2gua        cc:                                                                       
          >               Subject:     RE: ASCE 7-98 Wind Provisions                                
                    04:16 AM                                                                                       
                    respond to                                                                                     

I've finished a run through of ASCE 7-98's wind loading provisions for a
project here on Guam.  I was comparing the wind loading requirements for
UBC94 (still our current code), ASCE 7-95 and 7-98, and found out that 7-98
results in a 15 to 20% reduction in service level design wind pressure for
components and cladding in structures with h>60 ft.

The main reason, I think, is the change in exposure category for shorelines
in hurricane prone regions.  These areas are now specifically categorized
C, as opposed to D in 7-95 and UBC94 (by default, really).

Our building department is currently in the process of adopting the IBC,
which will make ASCE 7-98 an official code document.  I was wondering if
other engineers in hurricane prone areas are aware of their building
departments changing to IBC, and the possible ramifications of the reduced
design wind pressures (assuming I did the calcs correctly, but I'm pretty
sure I got it right).

This is a concern for us, because there have been many instances of windows
in hotels here (not ours :) ) being blown in/out during typhoons, right up
to 1998.  Granted, airborne debris and shoddy construction may have been
contributing factors, but it happened none the less.

If anyone on the listserver is aware of this issue coming up wrt their
code, I would appreciate any comments.

T. Eric Gillham PE