Positive Roof Wind Load 1

[CTSeng]

Is anyone designing roof structure specifically steel joists for the positive (non-uplift) wind? If so do you combine the positive wind with the roof live?

I have never heard of this and it seems like overkill. In high wind situations I'll check to make sure the positive roof wind is less than the roof live, which is virtually always the case. My logic is that the roof live will never occur at the same time as the worst case positive wind load.

Any thoughts are appreciated.

 

[Lion06]

The code has specific load combinations.
See ASCE 7-05 (or ASCE 7-02). You must combine wind with live, but not both at a factor of 1.
Also, I am curious as to how you are getting a positive wind pressure for your roof. For a normal structure (enclosed), I don't think you get any positive pressure on the roof until the pitch of the roof reaches 45 degrees. I would guess that is not the case if you are using steel joists.

 

[WillisV]

StructuralEIT - you are required by code to design for a minimum of 10psf wind load in any direction (even positive on roofs).

 

[Lion06]

WillisV-
Thank you for the clarification. Can you point me in the right area of the code to find that?

 

[JedClampett]

You need to look at Figures 6-11 A through D in ASCE 7-02 (I don't have ASCE 7-05 yet). Each of the graphs identify a positive and negative pressure for design. While the positive is usually less, it must be considered. Plus, it must be combined with the internal pressure coefficient from Figure 6-5.
The 10 psf minimum is in Section 6.4.2.1 and 6.4.2.2.

 

[WillisV]

Jed, I was thinking of the overall minimums (you pointed to the provisions for only the simplified procedure). The ones I was referring to are in:

IBC 2000 1609.1.2
IBC 2003 by Ref to ASCE 7-02, 6.1.4.1 and 6.1.4.2
IBC 2006 by Ref to ASCE 7-05, 6.1.4.1 and 6.1.4.2