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RE: through-truss without top chord bracing

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>Can any of you recommend a reference for the design of a
>through-truss (pony truss?) without top chord bracing?  I have
>seen trusses - such as gangways - where the top chord
>"appears" to be unbraced.  In actuality, they must use the
>stiffness of the vertical web members to resist the lateral
>buckling of the top chord because there is no way for the top
>chord to be considered as unbraced for the entire span of the
>truss and still be able to take much compressive load.  Are any
>of you familiar with a design procedure for this type of system?
 
1999 LRFD Specification Section C3.4 covers beam bracing with provisions for the required strength and stiffness of torsional bracing in subpart 4b. Also, we have the lecture notes from the AISC/SSRC short course on stability bracing. Many topics are covered, including the Pony Truss (that's what they're called) concept above. Essentially, those lecture notes illustrate the application of the equation in the LRFD Specification.
 
You'll find the LRFD Specification in your 3rd Edition LRFD Manual or available for free download at:
 
 
or with some other related information here:
 
 
A photocopy of the AISC/SSRC stability bracing short course lecture notes is also available from the AISC Steel Solutions Center for $25. Call 312/670-2400 (and press 1 when prompted) or send an email to solutions(--nospam--at)aisc.org.
 
Charlie