Structural response of thermoplastic basalt FRP-RC and BFRTP-steel hybrid-RC columns at full scale under cyclic lateral loading

This study investigates the cyclic lateral response of real-scale reinforced concrete (RC) columns reinforced with basalt fiber-reinforced thermoplastic polymer (BFRTP) bars, focusing on the role of BFRTP in compression. Three real-scale column specimens were tested: a conventional steel-reinforced RC column (steel-RC), a BFRTP-reinforced column (BFRTP-RC), and a hybrid column combining BFRTP and steel bars (hybrid-RC). A three-dimensional nonlinear finite-element (FE) analysis was also conducted to assess the influence of key factors. The BFRTP-RC column exhibited elastic, self-centering behavior with negligible residual drift, but limited ductility and energy dissipation due to premature concrete crushing. The hybrid column achieved higher peak strength and markedly improved ductility by combining steel plasticity with the high tensile capacity of BFRTP, while retaining smaller residual drifts than the steel-RC column. FE analyses incorporating a compressive reduction model for BFRTP successfully reproduced the experimental behavior and provided further insight into the failure mechanisms. Sensitivity analyses confirmed that the compressive characteristics of the BFRTP bars critically affected the peak strength and post-peak behavior of the BFRTP-RC columns, whereas the hybrid-RC columns exhibited stable performance regardless of the BFRTP properties. Additional simulations showed that high-strength concrete can mitigate compression-related weaknesses and improve the overall performance. These findings highlight the potential of hybrid reinforcement systems or design strategies, such as the adaptation of high-strength or ductile concrete and confinement or jacket reinforcement, to address the current limitations of FRP-RC vertical members. The knowledge obtained in this study will contribute to the advancement of seismic-resilient RC structures using BFRTP reinforcement.