J-integral approach for main crack propagation of RC beams strengthened with prestressed CFRP under cyclic bending load

Compared to the passive bonding strengthening technique using carbon fiber reinforced polymer (CFRP) for reinforced concrete (RC) structures, an active strengthening technique with prestressed FRP for reinforcing RC bridge structures with crack-like defects can make the stress distribution more reasonable, and can inhibit crack propagation. In this study, experimental and numerical methods were applied to investigate the fatigue crack propagation behavior of RC beams strengthened with prestressed carbon fiber laminate (CFL). Fatigue crack propagation tests were carried out to obtain the crack propagation rate on RC beams strengthened with CFL, which had different prestressing levels (0%, 15%, and 22%). The digital image correlation (DIC) method was used to capture the fatigue crack pattern. The finite element method was applied to calculate the J-integral of the main crack on RC beams strengthened with prestressed CFL. For accurate description of the fatigue crack propagation and fatigue life prediction, fatigue crack propagation tests were conducted. Based on a theoretical derivation, a modified version of Paris' law was proposed. Compared to RC beams strengthened with non-prestressed CFL, the main crack propagation rates on RC beams strengthened with prestressed CFL having prestressing levels of 15% and 22% were decreased by 38.6% and 43.0%, respectively. Higher prestressing levels contribute to a greater resistance to crack propagation.