Open Structures and the National Building Code of Canada

[Woody1515]

Hello,

I have a question regarding “open” structures and the National Building Code of Canada. By an open structure, I mean a free standing canopy of sorts, with posts, beams and some sort of roof system (trusses, rafters, etc.). There are no walls, just the posts that transfer all loads to the foundation. I’m trying to think of a way of calculating the wind loads that act on the roof system. I’ve searched the NBCC and do not see any provisions for an open structure... Can I still use the values from Figures I-8 to I-14 to determine the wind loads, with using the Category 3 internal pressure coefficients? Or is there another method I am not seeing?

 

[Woody1515]

It is also my understanding that internal wind pressures develop due to a difference in atmospheric pressure between the inside and outside of a building... since the whole building is “outside”, is there no internal pressure and just external pressure?

 

[jayrod12]

I don't have a definitive answer for you, however the instances I have had to design these I've used the following method

1) for lateral wind, I use the C&C type wind loads applied to the projected area. I generally give this a healthy rounding up because inevitably people want to put up tarps when it's super windy or rainy to block certain sides
2) For uplift, I've used the OC, OS, OR, values as if it is an overhang. This is probably overly conservative, but I feel comfortable after.

If you were trying to design a hundred of these where being fine tuned might save significant material costs, then I'd be looking to trim down the loading noted above. But so far they have only been one off designs as part of a larger project where the additional costs of the canopy end up being minor in the overall construction costs.

 

[dik]

For oddball structures, I still use the 1965 wind pressure coefficients from that ancient code for the odd thing.

Dik

Dik