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ASCE7 Wind Load on Lattice Framework and Trussed Tower

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RFreund

RFreund

Structural
Aug 14, 2010
1,885
In regards to ASCE7 -05 or -10 do I have the following correct?

Lattice Framework:
Ratio of Solid Area to Gross Area - Use area of of the face of the elevation (or plane) that you are analyzing. Meaning that if you had a square section tower the solid are would only count the windward face of the front member. You would not count the front and back windward member face areas.
Area Af - This area includes both the windward face area of the front and back members.

Trussed Tower:
Ratio of Solid Area to Gross Area - Use area of of the windward face of the elevation (or plane) that you are analyzing. Meaning that if you had a square section tower the solid are would only count the windward face of the front member. You would not add the front and back member face areas.
Area Af - This area includes the windward face area of the front members ONLY.

So the difference is that Trussed towers deal with the projected area on a plane for both the ratio and the force (almost as if shielding is already considered) where as lattice frame work uses the projected area for the solid ratio but then applies the wind to all members windward face.
Thanks in advance!

EIT
 
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RF...a lattice framework is assumed to exist in one plane. A trussed tower has multiple planes, each contributing (to some extent) to the projected load. So yes, your assessment is correct.
 
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Sorry for busting in, but what is the current practice. At one time it was only one plane face in X-X was considered, then the Y-Y plane face, resulting in the truss being designed separately in each of two planes. I never understood why, if for example the tower was roughly square, why a wind in a plane of 45 degrees off the main axes was not considered. It certainly seems that it would give maximum column loads, with the two colums at the truss' "neutral axis" in the 270 degree plane and the two columns carrying all the load in the 45 deg plane. Still only the main X & Y planes are analyzed separatley?

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
 
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I noticed that I put this in the Thread group - sorry for this.

Ron -
Response is leading me to beleive that I have it backwards. Let me explain further.
Lattice Framework:
Ratio of Solid Area to Gross Area - Use area of of the face of the elevation (or plane) that you are analyzing. Meaning that if you had a square section tower the solid are would only count the windward face of the front member. Update:[/i] Meaning if there is an angle on the front face you have the area of the windward face of this angle. The angle that is on the back face (say 18" back) and is covered by this angle does not contribute to the solid area.[/i] You would not count the front and back windward member face areas.

Area Af - This area includes both the windward face area of the front and back members. Update: Meaning the angle on the front face receives wind pressure and the angle on the back face receives pressure even though its is 'covered' by the front face angle.

Trussed tower:
Ratio of Solid Area to Gross Area - same as Lattice frame work.

Area Af - Use the same solid area as used in the Ratio above. Do not apply wind load to members 'covered' by members on the front face of the tower.

This is still correct or do I have this backwards?

Thanks again!


EIT
 
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