Inelastic buckling of torsionally braced I-girders under uniform bending: I. Numerical parametric studies

This study examines inelastic buckling of discretely braced I-girders by diaphragm bracings and torsional stiffness requirements to attain nominal flexural design strengths. To simulate the torsionally braced multi-girders, 2-girder and 4-girder systems interconnected with I-shaped cross-beams were numerically modeled by using 3D finite elements. Incremental nonlinear analyses considering the initial imperfections and residual stresses were conducted, and the effect of torsional bracing stiffness on inelastic lateral torsional buckling was evaluated. Based on the parametric analysis results, the torsional stiffness required attaining the inelastic buckling strengths specified by the AASHTO LRFD and Eurocode 3 was examined. It was found that the current design provisions suggested by AISC and SSRC overestimate the required torsional stiffness and may lead to an excessively conservative design. Improved information on the design criteria for the torsional bracings is provided.