Velocity Pressure Equation 1

[aaron1111]

Hi everyone,

I'm analyzing a machine to be mounted atop a building, and need to determine the wind load acting on the machine. In ASCE 7-10, the equation for velocity pressure qz is

qz = 0.00256*kz*kzt*kd*V^2

In this equation, what value is V: Vult (from the basic wind speed map) or Vasd? (Vasd = Vult*Sqrt(0.6))

I have a Risk Category II structure in Exposure B, located in the upper midwest. According to the building code official, the design wind speed is 90mph. However, the wind speed map (which is for Exp C, mind you) says V = 115mph. Any help would be appreciated.

(I know I'll need to determine the factors G and Cp as well. But this first step has tripped me up.)

 

[sandman21]

If you look at the maps in ASCE 7-05 it likely 90mph, which is 115mph ultimate. Likely the person does not know that wind speeds have "changed".

 

[JStephen]

Find out what building code they're using, look in Chapter 35 and see which year of ASCE 7 it references, and that should resolve the issue.

 

[aaron1111]

Hey guys,

Thanks for the prompt reply. They're using a state building code that references ASCE 7-10. I'm disturbed that the building code official I spoke with has told me that the design wind speed is 90mph. Regardless, which value should I be using in the equation for V, 90 or 115?

Also, is this regardless of the exposure category? (Recall that the wind speed map is for exposure category C, while my project is in Exposure B. Perhaps the other factors in the equation account for the different exposure category?)

 

[wannabeSE]

If you are using ASCE 7-10, use 115mph. Just, remember to use ASCE 7-10 load combinations. For many (most) locations, the end result will be same. Except, ASCE 7-10 has different GCp for roof top equipment. I have had similar experiences when calling a building departments for wind speeds in special wind zones. The ATC has an online tool for wind speed:

http://windspeed.atcouncil.org/

The exposure is adjusted with the k_z (k_h) coefficient.

 

[dik]

wanna... great source...