flexible vs. non-flexible wind structure

[mnovicki]

anyone know where I can find in ASCE how to calculate the natural frequency of a building for wind? (flexible vs. non-flexible.... 1 Hz criteria) Can I use 1 / the approximate building period from seismic section 12?

 

[WillisV]

http://www.structuremag.org/Archives/2008-6/C-CS-BuildingPeriods-Jacobs-June08.pdf

 

[enginerding]

Maybe WillisV's article says this same thing (I don't have time to read it now), but it is more conservative for seismic loading to have a low period, but for wind it is more conservative to have a high period. Accordingly, the approximate equations in Chapter 12 of ASCE will tend to underestimate the period of a structure, whereas for wind this could be unconservative. However, unless you are close to the threshhold, I think the Ch12 approximation will be fine.

Chapter 15 (I know this is still for seismic) has a rational approach to calculate the natural frequency. See 15.4.4. This is presented because "other structures" do not fit under the assumptions used to come up with the Ch12 approximation. This method is pretty accurate. However, unless it is easy for you to calculate the deflections by hand, it is probably just easier to use a computer program to come up with the frequency.