Lateral-Torsional Buckling Response of Welded Wide-Flange Girders

Lateral-torsional buckling is a failure mode characterized by coupled lateral movement and twisting within an unbraced length of a steel member under flexure. The current Canadian steel design standard, CSA S16-14, prescribes unified design equations for predicting lateral-torsional buckling resistance that do not distinguish between rolled and welded sections. Results of recent numerical studies have shown that the current design equations to determine lateral-torsional buckling resistance may be unconservative for welded wide-flange steel girders. This is attributed to their welded nature, which produces residual stress distributions very different from rolled sections and may reduce their lateral-torsional buckling resistance. Furthermore, the design equations were developed based on studies using welding and fabrication methods that differ significantly from today's practices. Given the extensive use of wide-flange steel girders in building structures and bridges, there is an urgent need for better understanding and improvement of lateral-torsional buckling provisions in North American design standards. In this paper, S16's adequacy is examined by means of physical testing, with the aim of obtaining critical inelastic buckling moments. Test frames that allow out-of-plane movement (while maintaining continuous vertical load application) are implemented. Eleven large-scale specimens with laterally and torsionally pinned end conditions are tested to examine the effects of the cross-section geometry, residual stress distribution, and fabrication and welding procedures on the inelastic buckling resistance of welded wide-flange steel girders. The results of pre-test analyses aid in the design of test girders that are most affected by lateral-torsional buckling.

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