Cyclic Stress–Strain Model for Circular Concrete-Filled Steel Tubular Columns

Concrete-filled steel tubular (CFT) columns are becoming more widely used because of their superior strength and ductility. Another benefit of CFT is that it eliminates the need for formwork during construction. The accurate behavior of concrete under compressive cyclic loading is particularly important for the seismic-resistant design of structures, as the tensile strength of concrete is often neglected in the design of steel–concrete composite structures. In the present study, a confinement model for cyclic compression has been proposed which can predict the behavior of concrete confined in a circular CFT column. The proposed model is inspired by the previous models of cyclic axial compression developed for concrete confined either with steel reinforcement ties or with fiber-reinforced polymer (FRP). The main components of the cyclic model, i.e., the envelope curve and the loading–unloading curves, are suitably modified to accurately represent the behavior of concrete in a CFT column. In addition to the concrete strength, steel tube strength, and tube diameter-to-thickness ratio, the proposed model also considers the effect of the length-to-depth ratio of the CFT column. Further, the proposed model has been validated with the experimental results and can reasonably predict the peak as well as post-peak behavior.