Seismic behavior of RC columns under high active confinement force

This paper details the invention of a tensioning and anchoring device based on the "wedge-cutting effect" that can tension and anchor multi-layer carbon fiber reinforced polymer (CFRP) fabric. To achieve a high active confinement effect on an RC column, the device is characterized by its capability to lift the applied prestress to the greatest extent and minimize prestress loss. All eight RC columns with identical structural dimensions were designed and fabricated, including three unstrengthened and five strengthened columns. The seismic performance test and finite element simulation were conducted under a low cyclic reciprocating load. The test parameters include active confinement force and axial compression ratio, with active confinement force varying as a function of the number of layers of CFRP fabric. The results indicate that the seismic performance of RC columns with high active confinement can be significantly improved. Under a high axial compression ratio, the maximum displacement ductility coefficient and ultimate drift ratio of specimens strengthened with four layers of prestressed CFRP fabrics can increase by 87% and 152%, respectively, while the energy consumption can increase by 4.3 times. Additionally, the ultimate horizontal bearing capacity can be raised by 41%. The seismic performance of strengthened columns increases with the increase of active confinement, particularly under high axial compression. The finite element model is in good accord with the experiment. With an increase in active confinement force, the properties of confined concrete and CFRP are utilized to a greater extent, and more energy is dissipated by the opening and closing of numerous micro cracks.