Wind Speed Conversion Factors

[nutte]

The design wind speeds on the ASCE 7 maps are for a 50-year recurrence interval. The commentary for ASCE 7-05 provides a table in the commentary with conversion factors to apply to your wind speed for different mean recurrence intervals. For example, if you want an MRI of 5 years, you multiply your wind speed by 0.78 (for a 90-mph wind speed).

ASCE 37-02, Design Loads on Structures During Construction, has a similar table. Here, though, for a construction period of 2 to 5 years, the wind speed conversion factor is 0.9.

It would seem that these values should be the same. But for a 5-year recurrence interval, ASCE 7 provides 0.78, while ASCE 37 provides 0.9.

Is there something else involved here that makes these values different from each other? Also, does anybody here know how the values in the ASCE 7 table are calculated?

 

[spats]

Why would you expect the findings of two different committees to come to the same conclusions?

Recognize that ASCE 37-02 is based on ASCE 7-95, and thus is a somwhat out-of-date document. I can't find my ASCE 7-95 offhand, but wasn't wind still based on the fastest mile rather than a three second gust? Also, maybe different probabilities of being exceeded were used for each document. I have also never seen ASCE 37 included by reference in any model code, but the commentary of ASCE 7 is also not part of the "code".

 

[nutte]

ASCE 7-95 is based on the three-second gust speed. It contains the same wind speed conversion factor table that ASCE 7-05 does.

 

[ishvaaag]

Even if the parameter being evaluated is common, the whole dataset may not, nor maybe the statistical treatment, who knows if even there are nuances in the intent of one and the other; if not, on complete coincidence the tables should match.

I attach one Mathcad 2000 Professional worksheet on safety factors, structural reliability and so on that I made some years ago, these matters are tangentially touched but not ASCE based but from texts.