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Column Buckling Due to Unifoemly Distributed Load
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 Subject: Column Buckling Due to Unifoemly Distributed Load
 From: "h.d.richardson" <h.d.richardson(nospamat)telus.net>
 Date: Sun, 6 May 2012 13:16:08 0600
Fellow engineers,
I am working on
two freestanding stacks. A question has come up regarding maximum
permissible slenderness ratio, KL/r. AISC, CISC, and other structural
codes traditionally limit KL/r to being less than 200. ASME
SST12000 doesn't cover the subject. For KL/r AISC permits stress of
3.73 ksi whereas a stack axial stress will be about 10% of this
value.
I submit that limiting
KL/r to a maximum of 200 is much too conservative since the loading assumptions
for AISC and others are not applicable to stacks. Structural load
cases assume ALL loading in the form of a point load at the top and NO
uniformly distributed load while stacks have NO point load at the top and
ALL of the load is distributed along the height. Guyed stacks are a
different matter, of course, because most of the load comes from the force of
the guys or from the weight of other sections of the stack above the guys; I
would always restrict KL/r to being less than 200 got guyed stacks.
My thought was to solve
the Euler equation and use a safety factor of 2.5 or 3 but my skill with
differential equations is not what it used to be. The equation I am trying
to solve for UDL only is
EI(d2y/dx^2) = M
where
M= m* Integral (from x to L) of w*y*dx
M = bending moment
w = weight/foot
Any other thoughts,
references, or help in solving the equation would be welcome. Also, since
I'm never sure if I'm connected to the list or not any more, a direct response
would also be welcome.
Thanks in advance.
H. Daryl Richardson

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