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RE: 2006 IBC Wind Load question

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My understanding is that you don’t necessarily have to calculate the gust effect factor, you are permitted to take G=0.85 which the commentary identifies as conservative for most “rigid” structures.  Based on discussions in the ASCE 7 wind subcommittee, that default value is generally going to apply to your average low-rise commercial/residential/institutional building.  This has been borne out by examples circulated around the subcommittee that showed a typical low-rise building calculating out to G=0.82.  In fact there has been some talk about replacing some of the standard GCp values with just a Cp value that incorporates the G=0.85 default, as well as fixing the language so that it is clear that G=0.85 really is expected to be the default for normal buildings.




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


From: Garner, Robert [mailto:rgarner(--nospam--at)]
Sent: Tuesday, August 28, 2007 11:08 AM
To: seaint(--nospam--at)
Subject: RE: 2006 IBC Wind Load question


Hi, Dennis,


I went to a 2006 IBC Wind Design Seminar by Dr. Ghosh yesterday.  Of course, the IBC references ASCE 7-05 for wind design.  And the simplified method isn't really simple.  I concur with another on the list that it's probably best to learn the so-called analytic method.  It seems more simplified than the simplified method and covers any building configuration except those than must be done by wind tunnel.  Basic wind speeds are set by ASCE 7 Figure 6-1 and are 85 mph on the west coast.  There are a couple special wind regions in the west and wind speeds in those areas would have to come from local AHJ's.  I think your greatest joy will be experienced when you calculate the gust effect factor - this is rocket science here!


Bob Garner, S.E.

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