Need Guidance on Wind Load Calculation for Observation Tower with Roof in BC, Canada

[basharhijazi]

Hello,
I'm currently designing an observation tower in British Columbia, Canada. However, I've encountered some challenges in finding specific information in the building codes regarding wind load calculations for this type of structure.

My main concerns are:

Wind Load Calculation: The observation tower doesn't have walls, so I initially considered treating it similarly to a pedestrian bridge. However, pedestrian bridges typically don't have roofs, whereas my tower does, which complicates the calculation for roof uplift.

Roof Uplift: I'm unsure how to accurately calculate the wind load for the roof to ensure it is properly anchored and can resist uplift forces.

Has anyone dealt with similar structures, or can anyone provide guidance on the correct approach for calculating wind loads, especially for the roof uplift, in accordance with Canadian building codes (BCBC, NBC, or others)? Any references or examples would be greatly appreciated!

 

[TLHS]

Yeah, this is not well defined anywhere. There are a couple of things I'm aware of.

1) Use the worst case internal pressure coefficient. This is really conservative for most roofs and is clearly not the intent of the condition that is being described in the code. It's meant to be for buildings with big doors for wind coming in and then that wind being kicked around inside the building. However, this gives you something to point at in the Canadian code.

2) You can look to ASCE-7 for methodology. Their wind pressure has different return periods, and their gust modifier is different, but you can isolate that part out normally and use their general methods.

3) There are old diagrams for a bunch of different shapes of structures, including open structures. Some of these charts are still the basis for the current Canadian figures (Sourced from SIA 160, which is where the supplementary charts in the structural commentaries are mostly from). You'd need to study pretty carefully and integrate the right wind pressures and modifiers.

https://nrc-publications.canada.ca/eng/view/ft/?id=f1daa49c-b559-40c1-9b8e-dc6ecd35f527