ASCE 7 Wind Loading of Perforated Surfaces 1

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I am currently designing aluminum "fins" (about 12" wide x 4" deep) to hang from an existing 12-story building. They are being added solely as an architectural feature. In an attempt to limit the wind load force, we are exploring using perforated aluminum to fabricate the fins.

The perforations reduce the surface area of the fin by about 40%-50% but I cannot find any mention of how this would affect the wind loading in ASCE 7. All I can find is that the "design wind force shall be calculated based on the area of the structure projected on a plane normal to the wind area". To me, that means that these small perforations in the aluminum reduce the area and thus the total wind force.

Any thoughts or comments? Thank in advance!

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[civilperson]

The area is reduced as you have noted, however, the Cf factor for lattice frameworks or open signs becomes 1.6. Reference Figure 6-22, Page 75, ASCE 7-05.

 

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Thanks civilperson... it's amazing how much more I can get out of a document if I actually look at all the Tables IN the document. This does the trick.

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