Calculate Ultimate Load Using Wind Speed ASCE 7-05

[InspectorGeneral]

I am looking for information about using a wind speed increase (above the design wind speed) to compute the ultimate load value for a structures MWFRS. I have read some older post suggesting a value of 1.3 for increasing the design load wind speed to compute the ultimate load wind speed (DS*1.3). I have also seen DS*1.3^.5. Where DS is the design wind speed based upon the wind speed map in ASCE 7-05.

The ultimate load wind speed was then used in the calculation of the MWFRS to compute the ultimate load of the structure.

I am hoping to find a referred journal article on this topic, and how ultimate load changes over time (if it does), and what factors cause the change and a method for calculating the change (I know, I am asking a lot!).

Any help would be most appreciated.

Thank you,

The Inspector General

 

[paddingtongreen]

Unless things have changed since I retired, the design wind speed is the design wind speed. The basic wind pressure is then multiplied by a number of other factors. Then, the result is subject to the load factors in various load combinations.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[WillisV]

ASCE 7-10 is based on ultimate wind speeds. The main journal article source for this revision is as follows:

Ultimate Wind Load Design Gust Wind Speeds
in the United States for Use in ASCE-7-10
Peter J. Vickery1; Dhiraj Wadhera; Jon Galsworthy; Jon A. Peterka; Peter A. Irwin; and
Lawrence A. Griffis: ASCE Journal of Structural Engineering, May 2010.

Basing this on ASCE 7-05 though, the load factor is 1.6 on wind pressure (the load factor takes the design wind pressure 1.0W up to ultimate values at 1.6W). So if for some reason you need to know the conversion based on wind speed, you would use sqrt(1.6) = 1.27 based on force being derived from velocity squared.

This conversion is apparent in the new ASCE 7-10 maps which provide the ultimate wind speed for the majority of the country as 114 mph (=90mph x 1.27).