Design Wind Load Cases ASCE 7-10 Roof Application

[Eren Jaeger]

I just have a question regarding ASCE 7-10 Sec. 27.4.6 Design Wind Load Cases. Case 1 is understandable wherein wind loads were applied only in one direction but for cases 2-4 , I am somewhat confused for the application of roof wind loads. Wall wind loads were just a combination of wind pressures from two different directions applied on different surface areas but, in the case of roof, let's say, Wy for roof is applied for the whole surface area of roof. Same goes for the Wx for roof. So basically, if I apply cases 2-4, Wx and Wy for roof is applied for the same surface which is like applying twice the wind load (though I know, they are different in values). What do you usually do for the roof wind loads applying Sec. 27.4.6?

I hope I am clear in what I am trying to say. I would appreciate your inputs. Thanks!

 

[Eren Jaeger]

Hoping to get some reply from anyone...

 

[Lomarandil]

There doesn't seem to be consensus on this topic (there have been a few threads in the past, see:

https://www.eng-tips.com/viewthread.cfm?qid=285500

https://www.eng-tips.com/viewthread.cfm?qid=322346

etc)

My current practice is to consider the combined effects of wind in an X and Y direction for walls (lateral loading), but to take those concurrent with the maximum effect of the two on the roof (vertical loading) rather than the combined effect (~150%of the wind load for wind in one direction).

I primarily work with flat roofs, so I don't know if my stance would change for higher pitches.

----
just call me Lo.

 

[Eren Jaeger]

Thanks for the reply Lo. So I think it all depends on the engr's discretion and judgment. Anyways, I hope ASCE will shed light on this matter. Thanks!