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RE: live load to resist uplift from snow load?

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Jordan:
 
Engineers tend to be really sanctimonious when they are not working for a design build contractor and they hear about how low a peer who is can stoop. 
 
I told the guy that asked me about it to tell the designer to just do it.  I also found the part in the live load section that says for continuous members to load alternate spans IBC 1607.10   and said to tell them to just load the live load on the cantilever.
 
Respectfully,
Scott


From: Jordan Truesdell, PE [mailto:seaint1(--nospam--at)truesdellengineering.com]
Sent: Monday, July 31, 2006 1:01 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: live load to resist uplift from snow load?

You've got to be kidding.  Live load in the uplift case is always zero, assuming there isn't a negative live load case to consider. 

The case you could use from ASCE7-02/ASD is 2.4.1 (3) - D + H + F + (Lr or S or R). Note that there is no live load in that equation, and the quasi-live Roof Live is not combined with Snow.

That and it makes no reasonable engineering sense.  Heck, I'd go so far as to say the D in that equation should be run with a custom "light" dead load so as not to over-consider the balancing effect of an otherwise conservative dead load.
Jordan


Haan, Scott M POA wrote:
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?
 
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