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RE: length to be used for tension bracing kl/r

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According to an article in the AISC Engineering Journal
(by A. Picard and D. Beaulieu) ..."The restraint provided to
the compression diagonal by the loaded tension diagonal is
generally sufficient to consider that the effective length
of the compression diagonal is 0.5 times the diagonal length.
(KL = 0.5L) for out-of-plane buckling as for in-plane buckling."
The article is in the Third Quarter, 1987 issue.

Mark Pemberton, P.E.
Sacramento, CA

-----Original Message-----
From: Ken Peoples [mailto:kspeoples(--nospam--at)yahoo.com]
Sent: Thursday, June 28, 2001 7:14 AM
To: seaint(--nospam--at)seaint.org
Subject: length to be used for tension bracing kl/r 


I seem to be constantly coming up with bracing member sizes that are
controlled by kl/r instead of the force in the member.  I have been
using the full length of the member when evaluating kl/r.  My question
is this: for X-bracing angles that are designed for tension only with
the kl/r<300 recommendation, is it reasonable to use a length of 1/2
the actual length when the angles are bolted together at the center.  I
know that the other angle wouldn't give it much lateral support to
prevent buckling in one of the directions if I were designing for
compression, but to satisfy the l/r<300 recommendation for tension
members, I would think that it might be OK.  I understand from the AISC
9th ed. commentary on B.7 that the recommendation is made to "afford a
degree of stiffness such that lateral movement ("slapping" or
vibration) will be avoided. What approach do most engineers use?
Thanks for your thoughts.
Ken

=====
Kenneth S. Peoples, P. E.
Lehigh Valley Technical Associates
1584 Weaversville Road
Northampton, PA 18067-9039
ph: 610-262-6345
fax: 610-262-8188
e-mail: kpeoples(--nospam--at)lvta.net

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