Abstract: A great number of experimental and numerical studies focused on the FRP shear strengthening rectangular and T-section beams, and the several models for calculating FRP shear contribution have been proposed, which were introduced to the codes and guideline of different countries. The research on the FRP shear strengthening RC box beam, however, is rarely presented in the literature. In this study, therefore, CFRP shear contribution of strengthening RC box beam is predicted by existing experimental results and theoretical models. Five models from different codes about predicting FRP shear contribution have been reviewed and discussed. 181 FRP shear strengthening specimens with rectangular and T-sections collected from existing literature was calculated by the five models. Compared with experimental results, the predictions of FRP shear contribution have a certain scatter, but fib Bulletin 14 showed a relative accuracy in predicting the rectangular and T-section beams. Besides, based on the results from experiments of FRP strengthened RC box beam in shear, five models overestimated the FRP shear contribution because the effective strain of FRP sheets has been overestimated. Compared with other four models, the results predicted by fib Bulletin 14 are close to the experimental values, but still in unconservative side. Based on comparison of the effective strain of FRP calculated by fib Bulletin 14 and experimental values, a coefficient of 1.31, therefore, was also proposed, which divided the formula of the effective strain in the fib Bulletin 14 model according to the experimental effective strain in fiber. The model with the modified effective strain presented a rational prediction in CFRP shear contribution of strengthened RC box beams.

Key words: reinforced concrete, box beam, strengthened, shear contribution, carbon-fiber-reinforced polymer