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FW: Effective Length

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Chris,

Our company often gets involved in designing steel trusses and I can give
you advise based on that experience.  As a policy, we design all members in
the plane of the truss with a K=1 and a length based on the joint to joint
dimensions.  Often the chords are continuous and a reduction in K might be
accurate, but hardly worth the gymnastics.  For out of plane stability
analysis, one has to look for effective bracing points, whether it is metal
deck, "x" bracing, concrete floors or bridging.  The out of plane bracing
needs to be evaluated very carefully for both stiffnes and strength.

Several good references for truss design are the AISC Design Guide
"Industrial Buldings" and the LRFD Connections manual.

Even though our company designs the trusse webs for pinned conditions, we
also evaluate the truss for fixity at the connections and decide whether the
secondary stresses are significant.  Often they are not.

I hope that this is in line with your request.

Curt La Count
Jacobs Engineering
Portland, OR.
 ----------
From: Chris Towne
To: SEAINT List Server
Subject: Effective Length
Date: Monday, February 08, 1999 5:47AM

Does anyone know of any good literature about determining effective lengths
of truss members in compression?  Also, any comments from experience would
be appreciated.
 
Chris Towne, E.I.T.