Cyclic axial compression stress-strain model for FRP-confined concrete-encased cross-shaped steel columns

FRP-confined concrete-encased cross-shaped steel columns (FCCSCs) are novel composite columns developed in recent years. For the bearing capacity design and seismic design of FCCSCs, the development of an accurate cyclic axial compression stress-strain model is necessary. Considering such a demand, this paper presents the cyclic axial stress-strain model for FCCSCs. The model is informed by physical observation and test measurements from a series of experimental investigations conducted by the authors and other researchers. The proposed cyclic model consists of two main components, namely (1) the monotonic stress-strain envelope curve and (2) the cyclic rules and equations to describe the unloading and reloading paths. Moreover, the hybrid confinement effect of FRP tube and cross-shaped steel is considered in the stress-strain model through the effective confinement stress model, in addition to their influence on the transition and ultimate point of the envelope curve. Finally, the accuracy of the proposed model is verified with the current test results.