Nonlinear analysis of composite steel-concrete beams with open sections under combined bending and torsion

Based on the rotating-angle softened truss model theory, a three-dimensional truss model is presented for the analysis of composite steel-concrete beams with open sections under combined bending and torsion. In this model, each element of the section is subjected to two systems of stresses separately. A one-dimensional stress system resists the longitudinal stresses due to bending and torsion, and a two-dimensional stress system resists the shear stresses due to torsion. The two stress systems are combined through the compatibility of strains and the equilibrium of stresses in the longitudinal direction. The equilibrium equations, compatibility equations and the constitutive laws of materials are satisfied. Through the analysis of several available examples, this model can predict not only the ultimate strength of the composite member, but also provide a tool to obtain the entire load-deformation history after the cracking of the concrete flange.