ASCE7-16 CANOPY WIND LOADS

[Ramezsayed EIT]

Hi Guys

I am designing Aluminum canopy and I am using ASCE7-16 To determine the Wind load

it shows on page 381 the procedures of designing the canopy and I have two questions :

1- it is not clear which height do I have to use in to get the Velocity pressure exposure coefficient and the qh, the figure shows Hc and He and the notation shows "qh = Velocity pressure evaluated at height z = h, in lb/ft2 (N/m2)"

2-based on this statement "(GCp) = net pressure coefficients for attached canopies given in
Fig. 30.11-1A–B for contributions from both upper and
lower surfaces individually and their combined (net)
effect on attached canopies."

DO I have to calculate the upper and lower surface uplift separately and then add them together as the number will almost be the double.

3- do we have to treat the canopy as open building only ? what if the canopy is same width of the building do we have to add internal pressure and treat it as enclosed ?

 

[Gerber_EIT]

1. Since equation 30.11-1 defines velocity pressure qh at the mean roof height h, I would consider this to be the mean roof height of the main structure that the canopy will be attached to.
2. My interpretation of Figures 30.11-1A & 30.11-1B are that they are split into several different cases:

1. Using GCp for upper.​

2. Using GCp for lower.​

3. Using GCp for upper and lower (not the above two combined, but the positive GCp case shown in Figure 30.11-1A).​

4. Using GCpn for net case (possibly one uplift and one downward, depending on your hc/he ratio).​

This provides you with several different uplift/downward pressure cases to review and design for. Worst case will depend on your geometry and dead loads. I believe this is the correct interpretation due to the wording the code using explaining GCp: "net pressure coefficients for attached canopies...for contributions from both upper and lower surfaces individually and from their combined (net) effect on attached canopies"
3. Not sure what you mean by this. I would consider a canopy to be an appurtenance, unless it is somehow enclosed (then you might be partially open, but I still wouldn't consider it the same as the rest of the building). Regardless of the building width, how would it be possible for a canopy to see any form of internal pressure?

 

[Ramezsayed EIT]

Actually I misunderstood I though we have to deal with the canopy as overhang which is resolved already in the 2016 Code.

for the Gcp I don't see the reason of adding two figures and using the max of them, I the values in figure A shall be combined and compare it to values in Figure b and use the highest value. I am not sure.