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
...additional coefficients for facia if provided in canopies.
Do you think
canopies designed for wind down case also.
DL+WIND UP AND
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
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.