Interactive buckling failure modes of hybrid steel flexural members

The flexural strength of steel I-beams is influenced by the local and lateral-torsional instabilities, where the presence of shear also reduces the moment carrying capacity. The objective of this research is to investigate the interactive buckling modes for hybrid steel I-shaped flexural members subjected to uniform moment loading. A three-dimensional finite element (FE) model subjected to monotonic loading is developed using nonlinear buckling analysis. The analytical model was experimentally verified based on the results of six full-scale 3 m beams that were tested previously. An extensive parametric study is conducted for 526 FE models and different instability modes including local buckling, lateral-torsional buckling, and shear buckling modes are identified. Subsequently a classification is proposed based on slenderness to predict buckling mode shapes of flexural member. Attention is given to the interaction between shear and flexural buckling modes, and their effect on inelastic flexural capacity. The flexural strength is evaluated based on local and overall slenderness and interactive buckling behavior. Based on the obtained buckling modes as well as local and overall slenderness ratios, some mathematical expressions are developed and presented to determine the ultimate shear-moment capacity when lateral torsional buckling is also associated with interactive buckling modes in hybrid and non-hybrid I-shaped flexural members.