How to consider wind load on interior component of truss tower?

[szleok]

When I am reading the Figure 6-23 in ASCE7-05, I found something unclear.

I have a square trussed tower with 6 columns. There is an elevator shaft inside the tower. The shaft is enclosed but the truss tower is an open structure.


As "Guide to the use of wind load provision of ASCE7-02" says, "The force coefficients given in Figure 6-22 include the contributions of both front and back faces of the tower, as well as the shielding effect of the front face on the back face".

If the front face member can shield the back face, can we say it can also shield the enclosed structure in the middle? I saw people using hybrid method to assign both the open structure member outside and the component inside debate about the quantity issue. How much goes to the outside member and how much goes to the component inside is a question.

I also saw people assign wind load to the whole truss tower with equation from Figure 6-23 and assign wind load to the elevator shaft as an extra. But i think that's too conservative.

 

[csd72]

Good Question!

To give you an accurate answer we need a little more information - dimensions of the open lattice tower legs and the dimensions of the elevator shaft compared to the overall tower, what is going on/in this tower (antennae,mechanical equipment e.t.c.) all of these effect the overall wind pressure.

Assuming that there is no additional future wind area, I would tend to go a little conservative and take the worst of 2 cases.
1. The wind on the lattice tower components plus the wind on the elevator shaft as a solid tower.
2. Treat the whole overall dimensions as a solid tower.

This may be a flexible structure and may also need to have dynamic wind effects taken into account according with the code.

 

[szleok]

But for me, the method 1 seems too conservative.