ASCE 7 Force Coefficient and wind loads on truss towers

[Bridge_Man]

Hi,

I have a truss tower where am interested in calculating wind loads on.

ASCE 7-16 directs me to use figure 29.4-3 for truss towers, my question is the following: when I calculate the pressure based on GxCfxqz should I be using that pressure on all elements in the tower ? or only on the elements on the wind facing face of the tower ?

I was looking at an example from RISA (

https://purchase.risa.com/documents/webinars/Wind_Loading_Non-Building_Structures.pdf

- page 34 of the pdf)
where they divided Cf by a factor of (2) which makes me think they did that so they can apply the resulting wind load on all elements of the tower rather than the wind facing elements only.

Also, the range of Cf goes to 4 which makes me think it already accounts for wind shielding. in other words, if am doing a 2D analysis, I would probably take that pressure apply on it wind facing elements and that would be it.

Thoughts ?
Thanks

 

[CrabbyT]

I typically just use Cf = 2, define two load cases (WLx and WLz), then apply wind to the windward and leeward sides of the tower for each load case.

 

[Bridge_Man]

So I assume you are applying a CF of 2 so you can apply that wind pressure on both the windward and leeward . but I think you are doing it conservatively.

That means what am doing it right. using the CF per the code and divide that by 2, and then re distribute the same force on both leeward and windward sides of the tower.

Thanks !

 

[dauwerda]