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Re: UBC Wind Uplift on Fabric Shade Cover

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The 0.7 wind pressure coefficient is intended to be used for the roof structure.  With the narrow categories that are available to us in the 2001 CBC,  it appears the more appropriate category for your condition is the other minor structures (1.4 factor).  It is tempting to use the 0.7 factor because it minimizes the demand forces.  Much like in seismic applications however, we are prudent in using the higher forces for smaller elements and areas due to the lack of redundancy for those elements and connections.
Jeff Coronado, S.E.
West Covina, CA
----- Original Message -----
From: Bill Allen
Sent: Wednesday, October 31, 2007 10:17 AM
Subject: UBC Wind Uplift on Fabric Shade Cover

I have a client who is designing a fabric shade cover as part as an outdoor hospitality improvement. This will consist of fabric attached to steel cables spanning between two conventional structures. At first, I advised my client to provide enough sag in the cables so that the horizontal force due to centenary action is not significant, which he has agreed to do. I?m now considering wind uplift.


My question: Do I need to consider wind uplift on this structure using a Cq value of 0.7? I?m not really concerned about the shade device itself, but I am concerned about the loads it will place on the supporting structure.


Comments are most welcome.




T. William (Bill) Allen, S.E.


Consulting Structural Engineers
V (949) 248-8588 ? F(949) 209-2509