ASCE 7-10 Figure 29.5-2

[SteelPE]

I have a theoretical project where the client would like to build an open sign. The facade of the sign will consists of perforated panels which will be 50% solid and 50% open. For argument sake, the sign will be 10' wide x 20' tall. The code we will be using will be ASCE7-10.

I am a bit confused with figure 29.5-2 specifically note 3 which states: "The area Af consistent with these force coefficients is the solid area projected normal to the wind direction"

Using my example, is this area they refer to in this note 200 square feet or 0.5* 200 = 100 square feet because I can read this not both ways?

 

[Surya77]

Note 3 says solid area, so therefore I would neglect area of openings.

Having said that, to add margin, I would consider diagonal length i.e., (20sqrt(2) x 10)x 0.5 = 141.5 sqft

 

[wannabeSE]

The coefficients would not make sense if Af is based on the entire area (200 sq ft). If that were the case, a surface with flat sided members and 90% open (Cf = 2.0) would have a higher load than a similar surface with 30% open (Cf = 1.6). But, who says ASCE 7 needs to make sense.

 

[SteelPE]

I see your point wannabeSE. For some reason I keep thinking of epsilon as being the ratio of open area to gross area which is opposite to how it is calculated.

I guess the argument is that epsilon is calculated as the ratio of solid area to gross area.... meaning you would use the 100ft^2 in my example above.