Nonlinear Seismic Analysis of Circular Concrete-Filled Steel Tube Members and Frames

Accurate nonlinear formulations are necessary for the assessment of structures under seismic and other extreme loading. In this work, a three-dimensional distributed plasticity beam element formulation for circular concrete-filled steel tubes has been developed for nonlinear static and dynamic analyses of composite seismic force resisting systems. A mixed basis for the element formulation was adopted to allow for accurate modeling of both material and geometric nonlinearities. The formulation utilizes uniaxial cyclic constitutive models for the concrete core and steel tube that account for the salient features of each material, as well as the interaction between the two, including concrete confinement and local buckling of the steel tube. The accuracy of the formulation was verified against a wide variety of experimental results. The verification confirms the capability of the formulation to accurately produce realistic simulations of element and frame behavior.