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x brace question

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Here are some more references to add to the ones that have already been
mentioned.

    1. Stoman, S. H., "Effective Length Spectra for Cross Bracings." ASCE
Journal   
        of Structural Engineering. December, 1989.

    2. DeWolf, J. T., and Pelliccione, J. F., "Cross-Bracing Design." ASCE
Journal   
        of the Structural Division. July, 1979.

    3. El-Tayem, A. A., and Goel, S. C., "Effective Length Factor for the
Design of X-
        Bracing Systems." AISC Engineering Journal. First Quarter, 1986.

Generally, the references say that the tension brace can be used as a rigid
support to brace the compression diagonal at the connection point.  Reference
1 presents theoretical formulas to predict the effective length factor based
on elastic behavior.  If the ASD safety factor for elastic buckling (12/23) is
substituted into the formulas in place of the variable (actual load)/(euler
load), the effective length factor is 0.63 (based on the total length of the
brace).

Research performed by Astaneh for his Ph. D. Dissertation established that
Gusset plates provide a pinned connection for bracing that buckles about the
weak axis of the gusset plate.  This research was performed on gusset plates
with free lengths that were much larger than twice the plate thickness, as
specified in the UBC and the AISC Seismic provisions.  Also, the tests were
performed with cyclic loading.

The Tube Steel properties for the reduced wall thickness as mentioned
previously on the list, can be found in the new HSS manual by AISC.

Bo Dowswell
Structural Design Solutions
Birmingham, AL