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Re: canopy wind loads

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Hi akester,
thanks for ur advise and info.i would like to share that even i had faced a sitution where some vibrations/or movements  were seen in canopy when its columns were abt height 6.0meters unsupported.
I checked it in my software and found that deflection at top of columns were under control theoritically.
Probably i think we miss there was,resonance or lateral movement of canopy due to pressure of wind.
Now,question arise that how many faces shall be applied lateral force alongwith vertical force component of wind..i mean only facia or internal faces as well ??
Can we assume a full factor or reduced factor of lateral force and vertical force when checked in combination???
----- Original Message -----
From: akester
Sent: Monday, January 31, 2005 6:27 AM
Subject: canopy wind loads

You made some interesting points about canopy roofs, especially those mounted to a single central pole. I had never thought about resonance and its contribution to the failure. I could totally invision this happening. This is similar to the same way the bridge Galloping Girdy failed, as it twisted it exposed the deck of the bridge to the lateral wind because it had a vertical exposure. And as it twisted back and forth, each time gaining a little more twist, it further was exposed to lateral wind loads. In that case, it did not even take a very significantly high wind speed.
Raj Wrote: ...additional coefficients for facia if provided in canopies.
Do you think canopies designed for wind down case also.
i.e DL+LL

Is Third combinations is important ?? ...........Raj
For open canopy structures, I usually use sign wind pressures for vertical surfaces, as to me, this is the closest thing in ASCE to model it to. I would have a look at the wall pressures as well if it is a considerable concern on your structure. Remember, if the code is not clear on which pressures to use, you can always use your own judgement and use increased pressures in your design if you are not comfortable with something. Of course, with everything, economics comes into play.
The third combination in any case I have ever had, which I would use 0.6D + W, in downward pressure, would not be greater then D + L on a roof. For many roof shapes, such as a traditional sloped residential roof with a ridge, one side may have a negative pressure while the other side has a positive. This will not be greater then your gravity loads of D + L.