Behavior and theoretical model of FRP-RC columns under cyclic axial compression

Fibre-reinforced polymer (FRP) bars have been used as reinforcement for reinforced concrete (RC) structures to solve the problems associated with steel reinforcement corrosion. Although axial compression tests have been conducted and mechanical behavior of RC columns reinforced with FRP bars (FRP-RC columns) has been known to some extent, the cyclic compressive behavior of FRP-RC columns remains unclear. To tackle this research gap, an experimental study was conducted to explore the cyclic compressive behavior of FRP-RC columns, with effects of parameters including confinement stiffness (i.e., spiral pitch), reinforcement ratio and loading scheme being carefully explored. The experimental study reveals that, interestingly, the FRP longitudinal bars can significantly reduce the concrete plastic strains in FRP-RC columns (referred to as plastic strain recovery). It is also found that the axial load-strain curves exhibit a three-portion behavior, and the FRP longitudinal bars plays an important role in resisting the axial stresses. The existing model for FRP-confined concrete under cyclic loading fails to predict the axial cyclic behavior of FRP-RC columns. A new model for FRP-RC columns is proposed and the accuracy of the proposed model is verified against the test results.