Refined plastic hinge method for steel frames with local-global interactive buckling

In the conventional refined plastic hinge model, the section is assumed to be compact and the strength deterioration by local buckling is not considered. In this paper, a refined plastic hinge method for welded normal strength steel frames with H and box sections is developed to account for the local-global interactive buckling behaviour. Based on the exact stability solution of a beam-column subjected to axial force, shear force and bending moment, beam-column element with arbitrarily located plastic hinges is developed. Residual stresses and strain hardening effect are considered in the refined plastic hinge model. Accounting for the interaction between flange and web, a simplified design method for the post-buckling capacities of columns and beams is proposed and experimentally verified. The local buckling effect is incorporated into the beam-column element formula and the refined plastic hinge method considering the interaction of local-global buckling is then established. As validated by existing experimental results, the proposed refined plastic hinge method that only needs one element per member can predict the bearing capacity of welded normal strength steel columns and frames accurately and be easily employed into design practice.