NONLINEAR INELASTIC ANALYSIS OF STEEL BEAM-COLUMNS .1. THEORY

This paper presents a nonlinear inelastic analysis of the biaxial bending and torsion of thin-walled steel beam-columns based on the principle of virtual work. The effect of geometric nonlinearity is developed using position vector analysis. Approximations are not made in the early stage of the development, and thus some significant terms for buckling and postbuckling analysis are retained. The von Mises yield criterion, the associated flow rule, and the hardening rule are used in formulating the elastic-plastic constitutive matrix for the material inelasticity. Inelastic uniform and nonuniform torsion are incorporated in the formulation as well as the linear and nonlinear geometric effects of the loads. A corresponding finite-element model for the nonlinear incremental analysis of biaxial bending and torsion of thin-walled beam-columns is presented by using the principle of virtual work. Numerical results in a companion paper indicate that the model presented is capable of making accurate nonlinear analyses including postbuckling analyses.