Monotonic and cyclic compression behavior of axially loaded FRP-confined concrete-encased cross-shaped steel columns

This paper presents an experimental investigation of the axial compressive behavior on a novel composite column, namely, fiber-reinforced plastic (FRP) tube confined concrete-encased cross-shaped steel columns (FCCSCs). Totally of 36 specimens were tested under monotonic and cyclic axial compressive load. The main variables were the geometric parameters of the cross-shaped steel, FRP tube thickness, and the nature of loading (i.e., monotonic and cyclic compressive load). Experimental results show that FCCSCs have excellent axial load-bearing capacity at a relatively low steel content (less than 9.00%). This novel component of the cross-section significantly improves the peak stress of confined concrete and can achieve ductile failure and maintain good deformability. A suitable gap between the outer FRP tube and the insider steel section, that is, leaving a proper concrete cover, can effectively avoid premature failure of FRP tubes caused by the outward buckling of the steel. Based on the test results, a new confinement pressure model that considers the hybrid confinement of FRP tube and cross-shaped steel is proposed. Finally, the axial load-bearing capacity model of FCCSCs is developed based on the test results of this and existing studies.