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Re: Load Combination, Using Strength Design

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I have a flat roof. The only wind load on the roof is uplift. I am using eq. 16-3 and set the wind load to zero. Just want to make sure that this is not overly conservative!
 
Thank you,

Farzin S. Rahbar, SE
Vice President
David C. Weiss Structural Engineer & Associates, Inc.
(818) 227-8040 Ex. 13 Fax: (818) 227-8041


-----Original Message-----
From: Jason Christensen <jason(--nospam--at)wcaeng.com>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Sent: Tue, Aug 31, 2010 9:43 am
Subject: RE: Load Combination, Using Strength Design

If you are using the ASCE 7 wind loads you should have both an upward acting wind load and a downward acting wind load. 
 
If for some reason you don’t have an upward wind load then IBC equation 16-3 would be the controlling load combination for the roof live load.
 
Jason Christensen, S.E.
 
From: fsrahbar(--nospam--at)aol.com [mailto:fsrahbar(--nospam--at)aol.com]
Sent: Tuesday, August 31, 2010 9:46 AM
To: seaint(--nospam--at)seaint.org
Subject: Load Combination, Using Strength Design
 
List:
 
IBC 2006, Eq. 16-3: 1.2D + 1.6Lr + 0.8WL
 
The wind load is always uplift. Therefore, it will actually help the roof live load. In your opinion, do I have to set the wind load as zero in this combination?
 
If so, why do they also have Eq. 16-2, with only 0.5Lr? Or, why don't they have another equation with just DL and roof live load?
 
Thank you,

Farzin S. Rahbar, SE
David C. Weiss Structural Engineer & Associates, Inc.
(818) 227-8040 Ex. 13 Fax: (818) 227-8041