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RE: live load to resist uplift from snow load?

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Scott,

 

I would not consider the use of live load to reduce the uplift from snow load.  Under the UBC there are several indirect references that would support your position.  1607.2 Critical Distribution of Live Loads requires design loading conditions that would create the maximum shear and bending moments (uplift is maximum shear in the opposite direction).  1607.3.2 Distribution of uniform floor loads requires alternate and adjacent span loading.  1607.4.3 Unbalanced loading requires the use of unbalanced loads that will require larger members or connections (uplift connection) for roof loads.  1612.1 Combinations of loads states that the most critical effect can occur when one or more of the contributing loads are not acting.  1613 Deflection states that the most restrictive condition shall apply (use this in combination with 1612.1).

 

 


From: Haan, Scott M POA [mailto:Scott.M.Haan(--nospam--at)poa02.usace.army.mil]
Sent: Monday, July 31, 2006 11:35 AM
To: seaint(--nospam--at)seaint.org
Subject: live load to resist uplift from snow load?

 

I was asked about using live load to resist uplift from snow load. The situation is wood trusses spanning 30 something feet sitting on the cantilevered ends of wood joists.  The designer wants to use live load so that the interior end of the joists do not need an uplift connection and the ends of the beam supporting cantilevered joists does not need an uplift connection.

 

 It seems intuitive to me that you should not use live load to resist uplift from snow because live load is make-believe and can be removed by definition and the live load and snow load would not necessarily occur at the same time.

 

I cannot find a code section or notes next to load combinations  that says you cannot do this.  However, I seem to remember a local home builders floor that started to bow up before  the 2 feet of stacked newspapers could be put on the cantilevered joists.

 

Does the code allow you to use live load to resist uplift from snow?  Does anyone ever use live load to resist uplift from snow or other live load for that matter?