Seismic performance of precast columns strengthened with prestressed CFRP

Abstract

To address the issue of poor seismic performance in precast columns compared to cast-in-place columns during service, a wedge-type anchor was designed to apply prestress to multi-layer carbon fiber reinforced polymer (CFRP) and strengthen the precast columns. Eight specimens were designed and fabricated to validate the strengthening effect of the proposed method. The seismic performance indicators, including ductility, energy dissipation, and load-bearing capacity of each specimen, were analyzed based on parameters such as the use of strengthening, axial compression ratio, and longitudinal reinforcement diameter (equivalent reinforcement ratio). The results showed that the ductility coefficient and energy dissipation of the strengthened specimens increased by up to 240% and 640% respectively, and the ultimate bearing capacity increased by up to 34.5%. With the increase in axial compression ratio, the ductility coefficient and energy dissipation capacity of the specimens decreased, but the load-bearing capacity increased. Increasing the diameter of the longitudinal reinforcement at an equivalent reinforcement ratio resulted in a decrease in the ductility and energy dissipation capacity of the specimens, but improved their load-bearing capacity and stiffness. This is because there is a stiffness transition in the connection area between the grouting sleeve and the top, and plastic hinges form at the upper part of the sleeve, resulting in a reduction in the effective height of the specimen. However, prestressed CFRP provides sufficient lateral active confinement stress to the specimen, greatly reducing the bond slip between the longitudinal reinforcement and concrete, and improving the stiffness transition in the grouting sleeve area of the precast column, thereby enhancing the seismic performance and overall integrity of the precast column. Finally, a calculation method for the flexural capacity of strengthened specimens considering the constraint effect of CFRP on concrete was proposed, and the effective height of the specimens was calculated based on the upward mechanism of plastic hinges in precast columns. The final calculation results had small errors, indicating that the proposed method has high accuracy and good applicability.