Axial compressive performance and prediction models of confined concrete cylinders made of BFRP-PVC composite tubes

In recent years, fiber-reinforced polymer-polyvinyl chloride (FRP-PVC) tubular cylinders have been widely used in civil engineering applications. Concrete-filled FRP-PVC tubes possess excellent mechanical behavior and high durability. In this work, a composite reinforcement system with basalt fiber reinforced polymer (BFRP) strips wrapped around the surface of polyvinyl chloride (PVC) tubes is proposed for existing concrete cylinders. In addition, the effectiveness of the composite reinforcement system is evaluated and the working mechanism is studied. Monotonic axial compression tests are conducted on 39 concrete cylindrical specimens, and the parameters studied includs the number of BFRP layers, the net spacing of BFRP strips, and the type of reinforcement. The test results demonstrate that the bearing capacity of specimens with BFRP strips was enhanced by 8.42% up to 45.43% compared to unreinforced concrete cylinders. While, the bearing capability of BFRP-PVC reinforced specimens increase by 26.54% up to 62.30% compared with the control group specimen. Furthermore, a strength model that considers equivalent constraint effect coefficients is proposed based on existing strength models. The difference between the predicted results and the experimental results is within 15%. Research has shown that the reinforcement effect of the composite system is significant, and the research results can provide reference for engineering practice.