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

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I attended one of the AISC lateral bracing seminars last year and this
question was brought up in relation to a compression brace.  I believe the
answer given was it is allowable to use 1/2 the length because some test
data had proved the other leg does provide adequate lateral resistance.  If
this is o.k. for a compression leg, it should be applicable to a tension
brace also.

Steve W Bigham, PE
Design/Project Engineer
Braden Manufacturing
Ext. 2256


-----Original Message-----
From: Ken Peoples [mailto:kspeoples(--nospam--at)yahoo.com]
Sent: Thursday, June 28, 2001 9:14 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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