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FW: sidesway web buckling - AISC 9th edition K1.5

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Ken,

I believe that the requirements you are looking at should be broken into two
components.  First look at the local effects of the concentrated force on
the girder web.  If the reaction is large enough, a stiffener may be
required to get the force from the column into the girder.  The second thing
to consider is the stability of the tension flange.  What's happening at the
concentrated load is the web is being squeezed into compression and the
tension flange may not have the stiffness to effectively brace one end of
the compression strut.  This is the sidesway web buckling requirement that
you are mentioning.  The connection of the W18's and W16's should provide
enough stiffness through a shear tab connection to the W24 girder.  It would
have been more critical if the girder had been very deep compared to the
beams.

Curt La Count
Jacobs Engineering
Portland, OR
 ----------
From: Ken Peoples
To: seaint(--nospam--at)seaint.org
Subject: sidesway web buckling - AISC 9th edition K1.5
Date: Thursday, July 13, 2000 1:13PM

I am checking for stiffener requirements of a beam
supporting a column.  I would think that this is a
simple one but maybe there is more to it:  I have a
48' long beam with a column sitting on it at 24'.  The
beam is 24" deep and is also supporting 18" and 16"
beams at 6' spacing (top of all beams are equal).  In
order to check the sidsway buckling per K1.5, I need
to know what "l" is.  "l" is defined as the longest
laterally unbraced length of either flange.  I think
this should be 48' for my case but I just wanted to
make sure that it would not be 24'.

Can someone direct me to a good example of the
calculations required to determine if stiffeners are
required for such a condition (I am not talking about
a moment connection - just a concentrated load like a
column sitting on top of a beam).  I'm pretty sure
that I am doing it correctly but the allowable loads
that I come up with (without using a stiffener)are a
lot higher than I would have expected.  It makes me
wonder why I see so many stiffeners under concentrated
loads.

Thanks in advance for your help.

Ken Peoples, P. E.
lvta(--nospam--at)fast.net


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