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RE: Load Combination, Using Strength Design

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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) [mailto:fsrahbar(--nospam--at)]
Sent: Tuesday, August 31, 2010 9:46 AM
To: seaint(--nospam--at)
Subject: Load Combination, Using Strength Design




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