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Wind Load - Internal Pressure coefficient Cpi by Natioanl Building Code of Canada

Wind Load - Internal Pressure coefficient Cpi by Natioanl Building Code of Canada

Wind Load - Internal Pressure coefficient Cpi by Natioanl Building Code of Canada

(OP)
What would an experienced engineer use for the internal pressure coefficient Cpi, by National Building Code of Canada User's Guide, for a cottage (seasonal home)? The cottage has casement windows that can be opened. Attached is the excerpt from the NBC User's Guide dealing with Cpi. The internal pressure (or suction) is pi = Ce Cpi Cg q I where q is the reference wind pressure corresponsing to a 1 in 50 year return period, Ce is exosure factor (0.9 in my case), Cg is gust factor (2.0), and I is importance factor (0.75 for deflection; 0.9 for strength).

My feeling is it should be "Category 2" (Cpi = -0.45, +0.3), but I am interested in what experienced engineers are using. Is anyone using categoty 1?

RE: Wind Load - Internal Pressure coefficient Cpi by Natioanl Building Code of Canada

I agree with your choice.

BA

RE: Wind Load - Internal Pressure coefficient Cpi by Natioanl Building Code of Canada

Cat 2 is common... have you looked into the requirements of Part 9 for both wind and snow of the NBC?

Dik

RE: Wind Load - Internal Pressure coefficient Cpi by Natioanl Building Code of Canada

(OP)
Thank you both. Much appreciated.

Yes I have looked into Part 9 - that was the first thing I did. Snow load factor is less in part 9, but I cannot find any reduction in wind load in Part 9. Since it is deflection under wind load that governs the design of this wind column that I am reviewing, and not strength, Part 9 does not seem to help.

Perhaps you can help in one other question: What should be the limit for the deflection under wind load? The member is a column in the exterior wall, extending 20 feet from first floor to the ridge beam at the peak of the roof (with no floor between first floor and peak of roof), supporting the ridge beam of the roof. There are 7 foot wide windows each side of this column, and the wall between the top of the lower window and bottom of the upper wondow is covered with drywall. According to the Wood Design Manual, the "suggested" deflection limit for "wind columms" is L/180. CSA O86.1-94 (I don't have the latest Standard here at home) does not seem to have any deflection limit for non-permanent loads other than L/180.

I am left wondering whether the limit should be L/360 because of the brittle plaster finish. What do you think? It seems to be that there is no Code requirement for this if it is a wall, only if a ceiling is involved.

RE: Wind Load - Internal Pressure coefficient Cpi by Natioanl Building Code of Canada

L/180 is a bit too limber for my liking but it is a judgment call. I would prefer L/360 if drywall is used.

BA

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