Lateral torsional buckling of I‐section simply supported beams with stepped height

Variable cross‐section beams are widely used, especially I‐section stepped beams with variable height, which have benefits such as saving materials to match the moment diagrams, reducing the structure height, and access for technical services. However, lowering the beam height also leads to a significant decrease in lateral torsional buckling resistance. Currently, the standards do not provide calculation rules for this type of beam yet, and some studies on lateral torsional buckling of beams have only focused on those with varying flange width and thickness while keeping the beam height constant. This article introduces an approximate formula to determine the critical moment of simply supported I‐section beams when the height varies. The proposed formula is validated by comparing with finite element simulation results obtained by COMSOL Multiphysics 5.6. The evaluation shows that the formula has a low coefficient of variation and high coefficient of determination, ensuring its reliability.