Cyclic axial compressive performance of the RC columns reinforced with FRP confined concrete core encased rebar

During an earthquake, the collapse of a structure is generally controlled by the failure or damage of its columns. It is important to enhance the seismic performance of reinforced concrete (RC) columns, including load capacity, ductility, and energy dissipation capacity. Column configurations with several small confined concrete components, namely, the confined concrete cores in this paper, are regarded as an effective way to improve the mechanical performance of square RC columns based on previous studies. The external confining material of a confined concrete core can be steel spirals, steel tubes, or FRP tubes. In this study, a new component, namely, FRP confined concrete core encased rebar (FCCC-R), and a new member, i.e., an RC column reinforced with FCCC-R were investigated. Eight RC columns with/without FCCC-R were cast and tested under cyclic axial compressive loading. The test result indicates that the RC columns reinforced with FCCC-R generally have a much higher axial load capacity. The axial load-displacement curves of all the tested specimens are compared, and the influences of the steel hoops, FCCC-R, and center FCCC are discussed. Moreover, the behaviors of different parts in a hybrid column, including steel hoops, and FRP tubes, are analyzed according to the strain development during the test. Finally, a section superposition method is proposed to predict the axial load-axial deformation behavior, whose results agree well with the experimental results.