Research on mechanical properties of high strength steel welded box columns (Ⅱ): second-order inelastic analysis

The residual stress distribution of high-strength steel is quite different from that of ordinary steel. The existing tangent modulus and stiffness degradation function are not suitable for the second-order inelastic analysis of welded high-strength steel box sections. While the refined plastic hinge model can reasonably consider the residual stress and the gradual development of plasticity through the tangent modulus and stiffness degradation function, and thus achieve similar accuracy to the plastic zone model. Therefore, a second-order inelastic analysis method suitable for welded high-strength steel box sections was proposed. The second-order effect of the element was considered through the stability function, and the bending effect was obtained based on the bending of the member caused by the rotation of the rod end and the resulting axial strain. In the refined plastic hinge model, the uniform distribution model of residual stress of welded high-strength steel box sections was adopted, and the calculation formulas for the tangent modulus of the welded box sections of different strength grades were constructed through the section analysis method. At the same time, the common axial force and bending were analyzed. By considering the effect of gradual yielding on the stiffness degradation of the box section, a stiffness degradation function that could simulate the plastic development of the section was established. Then, combined with the influence of the initiation and development of plastic hinges on the solution of the equilibrium differential equation, the elastic-plastic stiffness matrix of the beam-column element was established. It indicates that the second-order inelastic analysis method proposed in this study can estimate the mechanical properties of high-strength steel box sections and be employed into design of high-strength steel frame structures, providing a reference for the engineering application of the second-order inelastic analysis method. © 2022, Editorial Office of Journal of Building Structures. All right reserved.