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Re: Inverted tapered steel girders

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Are you saying that there are no lower flange braces to the purlins?  My experience is that the lower flange of the tapered roof beam would be braced on about 10' centers.  It should be possible to design roof beams without lower flange bracing however the roof beam will be heavier.  I'm not sure that it would be visually heavier.  You should be able to check for unbraced length and compact sections in a normal fashion.
 
HTH,  JH
----- Original Message -----
From: Jim Wilson
Sent: Tuesday, October 31, 2006 9:32 PM
Subject: Re: Inverted tapered steel girders

When I mentioned that the steel girders lacked diaphragms, I meant that they lacked any bracing between each other, as in bar joist construction.  The building has a metal deck and x-rod bracing for an overall diaphragm.
 
My query is to determine if there is a risk of a lateral torsional buckling type failure because the beam's lower flange is kinked.  I am guessing that at some point the flange could pull to the side as it tries to straighten itself out under load.   But that's just a hunch.
 
Jim

"sscholl2(--nospam--at)juno.com" <sscholl2(--nospam--at)juno.com> wrote:
Tapered steel girders are quite common in my experience. You didn't say what kind of diaphragm there was. It could be steel with or without lightwt. concrete. It will have to take horizontal shear from wind/seismic.
I assume that when you said the top chord was level you meant it was almost level but with slope for drainage.
 
Stan Scholl, P.E.
Laguna Beach, CA