A computer method for nonlinear inelastic analysis of 3D composite steel-concrete frame structures

摘要

This paper presents an efficient computer method for nonlinear inelastic analysis of three-dimensional composite steel-concrete frameworks. The proposed formulation is intended to model the geometrically nonlinear inelastic behaviour of composite frame elements using only one element per physical member. The behaviour model accounts for material inelasticity due to combined bi-axial bending and axial force, gradual yielding is described through basic equilibrium, compatibility and material nonlinear constitutive equations. In this way, the states of strain, stress and yield stress are monitored explicitly during each step of the analysis, the arbitrary cross-sectional shape, various stress-strain relationships for concrete and steel and the effect of material imperfections such as residual stresses are accurately included in the analysis. Tangent flexural rigidity of cross-section is derived and then using the flexibility approach the elasto-plastic tangent stiffness matrix and equivalent nodal loads vector of 3-D beam-column element is developed. The method ensures also that the ultimate strength capacity of the cross-section is nowhere exceeded once a full plastifled section develops. The proposed nonlinear analysis formulation has been implemented in a general nonlinear static purpose computer program. Several computational examples are given to validate the effectiveness of the proposed method and the reliability of the code to approach large-scale spatial frame structures.