Mixed Finite-Element Modeling of Rectangular Concrete-Filled Steel Tube Members and Frames under Static and Dynamic Loads

A computational study was conducted to investigate the nonlinear response of composite frames consisting of rectangular concrete-filled steel tube (RCFT) beam-columns and steel framing subjected to static and dynamic loads. Following mixed finite-element principles, a three-dimensional fiber-based beam finite-element model was developed, allowing slip deformation between steel tube and the concrete core. Comprehensive material constitutive relations were developed for the steel tube and the concrete core through examining the experimental results in the literature. The uniaxial stress-based steel and concrete constitutive relations include modeling of the effects of confinement, steel tube local buckling, cycling concrete into both tension and compression, cyclic softening, and other key cyclic phenomena observed for steel and concrete in RCFT members. The finite-element model was verified against a wide range of experimental tests under monotonic, quasistatic cyclic, and pseudodynamic loading conditions. The mixed finite-element model produced strong correlations with experimental results to simulate the nonlinear response of RCFT members with excellent computational efficiency.