Analysis of Composite Beam-Columns under Lateral Cyclic Loading

This paper proposes a reliable and computationally efficient beam-column finite-element model for the analysis of composite (steel-reinforced concrete) members of fully encased sections under cyclic loading conditions that induce uniaxial bending and axial force. The member is discretized into longitudinal steel reinforcement, steel shape, and concrete fiber elements such that the section force-deformation relation is derived by integration of the stress-strain relation of the fibers. The nonlinear behavior of the element is derived from the nonlinear stress-strain relation of the steel and concrete fibers, with consideration of buckling of the longitudinal reinforcement and steel shape. The model, which is incorporated with the DRAIN-2DX program, is calibrated and compared with experimental data from cyclic and pseudodynamic tests of fully encased composite beam-columns. The accuracy and efficiency of the model are demonstrated through the correlation between the experimental results and analytical simulations. The crushing strains of the concrete cover predicted by the analytical simulations were significantly higher in comparison with those suggested by theoretical stress-strain models. Based on the comparison with the empirical data, stiffness reduction is suggested for the fiber model analysis. Buckling of the longitudinal reinforcement appears to be the main cause leading to severe stiffness decay of fully encased composite beam-columns.