Moment Gradient Factors for Singly-Symmetric I-Sections

The lateral-torsional buckling behavior of singly-symmetric I-sections can be complicated due to significant variations in the sizes of the flanges. In many situations, the section is nonprismatic, which further complicates the lateral-torsional buckling behavior. There are substantial differences in the moment gradient factors in the AISC and AASHTO design specification. The AASHTO expression is relatively complicated to apply for realistic problems. This paper focuses on a parametric finite element study on the buckling behavior of singly-symmetric I-sections subjected to moment gradient. The study includes the effects of moment gradient on both prismatic and nonprismatic sections. Expressions in the commentary of the AISC specification are examined for application in bridge girders. Design recommendations are made for evaluating the lateraltorsional buckling behavior in both the positive and negative moment regions.

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