Impact torsional responses of CFRP-strengthened RC columns

External carbon fiber-reinforced polymer (CFRP) wrapping can effectively enhance the impact flexural and shear resistance of RC piers. However, its effect on impact torsion, a critical scenario that can occur in navigational bridges with double- or multi-column piers under oblique vessel collisions, has yet to be clarified. This study investigates the dynamic torsional responses of RC columns strengthened with CFRP under impact loadings. Torsional tests on RC columns with varying CFRP layers are conducted. Impact failure mechanisms and dynamic torque–twist responses of CFRP-strengthened RC columns under different loading rates are investigated through numerical analysis. An analytical model is proposed to predict the dynamic torque–twist relationship of CFRP-strengthened RC columns, and its accuracy is further verified through experimental results. Additionally, the reliability of the proposed model is further validated via numerical simulation of an actual bridge torsional failure case. The results indicate that CFRP strengthening changes the failure mode of RC columns from spiral cracking to compressive extrusion, significantly improving torsional capacity and ductility. Moreover, higher loading rates markedly increase peak torque and ultimate twist. The analytical model effectively captures key behavioral features, including torsional hardening, softening, and CFRP fracture. The predicted torque–twist relationships of piers are in close agreement with results obtained from experimental and high-fidelity numerical simulation results.