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Wind Load on Overhead Protection Canopies using ASCE 7-05

Wind Load on Overhead Protection Canopies using ASCE 7-05

(OP)
I require some assistance. I am designing an overhead protection canopy for a construction site in Ft Lauderdale, FL. I have done many of these in the past and have used ASCE 7-98 to calculate the wind loads on it. No problem there. However, I have a customer who requires the design to be checked off by Floida D.O.T. which requires the use of ASCE 7-05. Here is where my problem arises. The canopy is an open structure with a flat roof. It is 5' wide and 100' long and about 9' high. It is a temporary structure that is to be anchored to the foundation to resist wind loads. In 7-98, table 6-9 gives the Cf values for different monoslope roof dimension ratios between 5 and 1/5 for all heights. No problem figuring it there. However, 7-05 changed to a new figure, figure 6-18A, which gives values for Cn for different roof angles only. At the top of the figure there is a limitation for h/L to be between 0.25 and 1.0. My h/L is 0.09 or 1.8 depending on the wind direction. Can someone explain to me how to calculate the wind loads for this canopy using 7-05 or maybe explain to me how I can use this chart for my design?

RE: Wind Load on Overhead Protection Canopies using ASCE 7-05

Take a look at Fig. 6-18D and, in particular, Note 5: this addresses case of monoslope roof @ 0 degrees with h/L between 0.05 and 0.25. ...May also want to check out applicable errata: http://content.seinstitute.org/pdf/erratasheet7-05.pdf for some corrections/clarifications.

I'm not sure about when h/L is greater than 1.0 but I would probably look at the relevant references mentioned in the Commentary: see discussion for Fig 1-18 and C.6.5.13.

RE: Wind Load on Overhead Protection Canopies using ASCE 7-05

(OP)
This is great, except my value for the wind across the structure. This canopy is 5' wide and 10' tall. It runs about 100' along the sidewalk. There is a barrier wall along the construction side of the canopy roughly 2' away. Therefore, I have unobstructed wind flow when wind blows along the 100' direction and obstructed wind flow when the wind blows in the 5' direction. My h/L value for the first case is 0.1 and the h/L value for the second case is 2.0. I can use the figure 6-18D for the first case, but not the second. Any more ideas? Should I just revert back to 7-98 where I can actually figure the values, since 7-05 doesn't seem to work? Please help ladies and gentlemen.

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