Flexural Fatigue Performance Analysis of Bridge T-Beam Members Strengthened with Prestressed CFRP Plates

Prestressed carbon fiber–reinforced polymer (CFRP) plate strengthening has been widely applied in the rehabilitation of flexural bridge members due to its advantages of low self-weight, convenient construction, and excellent durability. However, existing studies have mainly focused on the static behavior of prestressed CFRP-strengthened beams, while the flexural fatigue performance of prestressed CFRP plate–strengthened bridge girders remains insufficiently understood. To address this gap, this study investigates bridge T-beam members through a series of flexural fatigue tests, including unstrengthened beams, beams strengthened with non-prestressed CFRP plates, and beams strengthened with prestressed CFRP plates. The evolution of mid-span deflection, stiffness degradation, strain responses of tensile reinforcement and CFRP plates, as well as the interfacial bond behavior under different strengthening schemes were systematically analyzed. In addition, the effects of fatigue damage accumulation on the residual static performance and ultimate load-carrying capacity of prestressed CFRP-strengthened beams were further examined. The experimental results indicate that, compared with unstrengthened beams and non-prestressed CFRP-strengthened beams, prestressed CFRP plate–strengthened beams exhibited smaller mid-span deflections, more stable stiffness degradation characteristics, and lower strain amplitudes in tensile reinforcement during fatigue loading, demonstrating a significant improvement in flexural fatigue performance. In contrast, beams strengthened with non-prestressed CFRP plates were prone to CFRP–concrete interfacial debonding under cyclic loading, which led to stress redistribution between the steel reinforcement and CFRP plates, resulting in a rapid increase in reinforcement strain amplitude and premature fatigue failure. Post-fatigue monotonic loading tests further revealed that moderate fatigue damage had a limited influence on the static load capacity of prestressed CFRP-strengthened beams, whereas more pronounced degradation in stiffness and load-bearing performance occurred under higher fatigue load levels. Overall, the results demonstrate that prestressed CFRP plates can effectively reduce the stress level of tensile reinforcement while maintaining favorable interfacial bonding performance, thereby significantly enhancing the flexural fatigue resistance of bridge girder members. This study provides experimental evidence to support fatigue strengthening strategies for existing bridges.