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RE: RISA, Lb-comp top and bottom

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FWIW, the default in Risa2D is to have the ends fixed when inputting a
member, so that may be the issue. 


> -----Original Message-----
> From: Eli Grassley [mailto:elig(--nospam--at)psm-engineers.com] 
> Sent: Thursday, February 16, 2006 1:37 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: RISA, Lb-comp top and bottom
> 
> John - you are on the right track with the way a bracing 
> kicker is used.  However...
> 
> That does not make sense that the design of your beam would 
> be changing if you brace the bottom flange of the beam.  If 
> you have a simply supported beam, there is NO compression in 
> the bottom flange, and thus no reason to brace it.  A simply 
> supported beam with absolutely no bottom flange bracing will 
> perform exactly the same as a simply supported beam with 
> bracing at 3" oc.  Whether or not RISA realizes this fact is 
> another question.  Check your model and make sure that the 
> local axis of the beam are oriented correctly and the end 
> supports are pinned.
> 
> ~~ Eli G
> -----Original Message-----
> From: john smith [mailto:steelstudent(--nospam--at)gmail.com]
> Sent: Thursday, February 16, 2006 10:35 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: RISA, Lb-comp top and bottom
> 
> So, Lcomp-bottom doesn't mean the bottom of the compression 
> area of the beam (ie. upper half of depth of the beam, the 
> bottom half being in tension)?  But the bracing length for 
> the bottom of the beam.
> 
> I was playing around w/ the value for Lbcomp-bot in RISA, and 
> it seems to pass my beam if i put a brace at midspan as a 
> minimum.  So they would build it w/ a 'kicker' from the roof 
> joist?  Is this a steel angle from the bottom of the joist to 
> the bottom of the beams i've seen? 
> 
> 
> Thanks again!
> 



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