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Subject: sidesway web buckling - AISC 9th edition, AISC 9th edition - eq K1-6

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Ken Peoples wrote:

. > 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.

-and-

. > Can someone tell me what "h" is in equations K1-6 and K1-7?

Thanks
Ken Peoples
lvta(--nospam--at)fast.net

Check your condition at the top flange.  Can the top flange rotate?  Does the
slab or diaphragm provide bracing of the top flange of the beam?  When you check
the other limit states in Chapter K are they all met?  Often stiffeners are used
for local flange bending, local web yielding, eccentrically applied loads,
compression buckling of the web, etc.  Check the controlling condition, if you
have a thick web beam and light loads from the column, the conditions may
actually work out by calculation.  However, I recommend using the LRFD for
confirming this condition as any new information gathered from research (and
there has been some in the last ten years) is not reflected in the ASD, only the
LRFD.  This is especially important and applicable to bracing and stability
isues.

h in equations K1-6, K1-7 is defined as the clear distance between the flanges,
minus the fillets (think unrestrained plate dimension).

Kevin Moore



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