This paper studied experimentally the behavior of circular fiber-reinforced polymer (FRP)–steel-confined concrete columns subjected to reversed cyclic loads. The influence of main structural factors on the cyclic behavior of the columns is discussed. Test results showed the outstanding seismic performance of FRP–steel-confined RC and steel-reinforced concrete (SRC) columns. The lateral confinement effectiveness of glass fiber–reinforced polymer (GFRP) tubes and GFRP–steel tubes was verified and a simplified OpenSees-based finite-element method (FEM) model was developed to simulate the experimental results of the test columns. Based on the proposed FEM model, a parametric analysis was conducted to investigate the effects of main factors on the reversed cyclic behavior of GFRP–steel-confined RC columns. Based on the test and numerical analyses, the study discussed the influence of variables such as the lateral confinement on the plastic hinge region (PHR) height and peak drift ratio of the columns under reversed cyclic loads. Results indicate that lateral confinement significantly affects the PHR height of circular confined RC columns. Based on the analyses of the data from this study and literature, a simple model was suggested to predict the peak drift ratio of confined RC columns.

The elliptical FRP–concrete–steel double-skin tubular column (DSTC) is a promising compression member due to its favorable mechanical performance and constructability. To provide insights into the interaction mechanism of the individual parts (i.e., elliptical FRP tube, elliptical steel tube, and sandwiched concrete), the compressive behavior of elliptical DSTC stub columns was systematically studied and compared with two types of reference specimens, including FRP-confined solid concrete (FCSC) and FRP-confined hollow concrete (FCHC) specimens. Based on a comparative investigation on the compressive performance and dilation properties of concrete cores in different column forms, a three-stage interaction mechanism in elliptical DSTC was clarified: unconfined stage, transition stage, and hardening stage. The confined concrete strength in elliptical DSTC increased by 20%–55% compared with the corresponding elliptical FCSC with the same column dimension and FRP confinement level. The possible reason is that the less-effective confinement zone in elliptical FCSC was replaced by a hollow steel tube. The existing model could not be directly adopted to predict the behavior of elliptical DSTC using high-strength concrete.