The potential complexities in the geometries of trusses can lead to either local or global stability problems. The effects of connection flexibility are not well understood in terms of the impact of the buckling behavior of the truss. Although there have been several studies on the bracing behavior of pure column or beam systems, very little work has been conducted on truss systems. Because of the variety of failure modes as well as the impact of connection flexibility, the stability bracing requirements for trusses have not been well established. Variations in structural geometries such the connection details between the chords and the verticals or diagonals, support conditions, load position on the cross section, as well as bracing details introduce significant complexity in understanding the fundamental bracing behavior. For example, the fundamental behavior of a pony truss is greatly different than that of a roof truss due to combinations of all of the above mentioned factors.This paper highlights the results of an ongoing research investigation at Ferguson Structural Engineering Laboratory at the University of Texas at Austin on the bracing behavior of truss systems. Full scale laboratory experiments consisted of buckling tests on two 72 ft. long trusses. Both lateral and torsional bracing systems were investigated. The impact of the number of braces as well as the brace stiffness was captured. For lateral bracing, the bracing was positioned at the top (compression) chord. Tests with the torsional braces included braces positioned at either the top or bottom chord. The torsional braces positioned on the bottom chord were consistent with pony truss applications where stability is provided by the floor beams. The test results demonstrated that the trusses are sensitive to load position similar to the behavior exhibited by beams. The results demonstrate that the bracing behavior is sensitive to the brace stiffness, cross section distortion, as well as the number of braces. On pony truss applications, the supports provided tipping restraint of the truss. Results from the laboratory tests have provided valuable data to validate FEA models that are being used to carry out detailed parametric evaluations.
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