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RE: Tributary Area

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You get fewer headaches if you think of the tributary area as a number that doesn't necessarily corresopnd to a particular piece of real estate on the supported floor.  This is especially true in the case of continuous beams.

MJ

"Nels Roselund" <njineer(--nospam--at)att.net> wrote:

>Steve,
>
> 
>
>I hadn't noticed 1607.6 before.  For my case, the two methods give nearly
>identical reductions: 0.90 for Section 1607.5 vs 0.88 for 1607.6.  Thanks.  
>
> 
>
>Nels Roselund, SE
>
>South San Gabriel, CA
>
>njineer(--nospam--at)att.net
>
>  _____  
>
>From: S. Gordin [mailto:mailbox(--nospam--at)sgeconsulting.com] 
>Sent: Thursday, August 11, 2005 11:21 AM
>To: Seaint@Seaint. Org
>Subject: Re: Tributary Area
>
> 
>
>Nels,
>
> 
>
>UBC1607.5: A=area supported by the member, i.e., 1/2 of the span of the
>purlin for the edge beam, A>150.  
>
>LL reduction for A>150 sq. ft. is R=0.08*(A-150). 
>
> 
>
>For A=300 ==>R=12%
>
> 
>
>Alternatively: 
>
> 
>
>UBC1607.6 (ASCE7 similar): AI=influence area, twice the tributary area for
>the beam,  i.e., AI=2*A, AI>400; 
>
>Reduced live load: L={0.25+15/[sqrt(AI)]}.
>
> 
>
>For AI=600 ==> L=0.86 (effective LL reduction R=14%).
>
> 
>
> 
>
>Both methods give similar results, but appropriate formulas and widths
>should be used.
>
> 
>
>HTH,
>
> 
>
>V. Steve Gordin, PhD
>Registered Structural Engineer
>Irvine CA 
>
> 
>
> 
>
> 
>
>----- Original Message ----- 
>
>From: Nels Roselund <mailto:njineer(--nospam--at)att.net>  
>
>To: seaint(--nospam--at)seaint.org 
>
>Sent: Thursday, August 11, 2005 9:20 AM
>
>Subject: Tributary Area
>
> 
>
>What is the precise definition of Tributary Area for figuring live load
>reduction?  The UBC defines it as the area of floor or roof supported by the
>member.  If a beam supports one edge of a simple-span floor, is the
>tributary areas the span of the beam times width of the floor, or is it half
>that area because the beam supports only half the floor [the other half is
>supported on the other edge]?  I've seen it done both ways, and have done it
>both ways myself.
>
> 
>
>Nels Roselund, SE
>
>South San Gabriel, CA
>
>njineer(--nospam--at)att.net
>
> 
>
>

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