STUDY ON ULTIMATE BEARING CAPACITY OF BIAXIAL COMPRESSION-BENDING STEEL MEMBERS WITH THIN AND SLENDER H-SHAPED SECTION

To investigate the ultimate behavior of H-section members with large width-thickness ratios under a combined biaxial compression-bending, the parametric analysis models of H-section members with different axial force ratios, web and flange width-thickness ratios and different loading angles were developed by ABAQUS. Material and geometric nonlinearity were considered throughout the whole analysis, and the finite element models were validated by previous laboratory test results. Based on the elastic-plastic stability theory, a criterion for determining the ultimate state of biaxial compression-bending members was proposed. For plastic-hinge sections, the ultimate state is defined as the occurrence of plastic hinge. For slender sections controlled by local buckling, the ultimate state is the initial buckling moment, with the occurrence of plate local buckling been accurately identified through the criterion. The ultimate interactive curves of biaxial bending moments were obtained by least-square method, within which complicated interactive effects of width-thickness ratios of web and flange and the axial force were noted. The ultimate interactive formula for biaxial moments considering the strain hardening effect of material and the correlation effect of plate was proposed. Not limited by section classification, the proposed method is proved to have good applicability and accuracy.