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RE: ASCE 7-05 Wind Load - Simplified Methods by S.K. Ghosh in

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The commentary for Chapter 6 in ASCE 7-05 provides a rule of thumb for determining what is a “flexible” and rigid” building for purposes of applying the wind load provisions.  If the ratio of the height to the minimum width of the building is less than 4, generally the building can be taken as rigid and you would not have to calculate the frequency.  If it exceeds 4 the building may be flexible and the frequency should be calculated.


The need to clarify the gust effect provisions was discussed at the recent ACSE 7-10 meetings.  The impression I got is that the intent was to have most typical buildings simply use the G = 0.85 factor and not to have engineers calculating the frequency for every building, unless you had a tall and/or thin building or a structure where you were concerned about the dynamic response.


And in fact the article noted that for their “flexible” building they got a G = 0.87 based on the frequency they calculated and observed that was close to the 0.85 simplified factor.




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