Moment Gradient Factor for Lateral--Torsional Buckling of T-Shaped Beams

Lateral--torsional buckling (LTB) is a potential limit state for steel beams. Particularly, T-shaped beams (referred to as beams with WT-sections) can be sensitive to this failure mode due to the presence of only a single flange. Current LTB capacity equations in both CSA Standard S16 and AISC 360 neglect the moment gradient effect by prescribing a moment gradient factor of 1.0 when determining the critical moment for T-shaped beams. This study aims to assess the adequacy of the current moment gradient factor (1.0) for LTB capacity of simply supported T-shaped beams through numerical studies. The elastic critical moments of thirteen representative T-shaped beams subjected to a constant moment, a point load, or a uniformly distributed load are determined numerically using LTBeam and ABAQUS, a free and commercial software, respectively. Numerical analyses using both tools led to the finding that the elastic critical moments of T-shaped beams are affected by moment distributions. This study implies that T-shaped beams should have approximately the same moment gradient factor as I-shaped beams when subjected to single-curvature loading. Further work is required to assess the adequacy of the current moment gradient factor (1.0) in predicting the inelastic critical moments for LTB of simply supported T-shaped beams.

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