Enhancing shear behavior of RC beams using an innovative prestressed CFRP system: Concept and experimental studies

Prestressed fiber reinforced polymer (FRP) has demonstrated significant superiority over non-prestressed FRP in strengthening flexural capacity of reinforced concrete (RC) beams. However, applying prestressed FRP to improve shear behavior of RC beams on-site remains a challenge, due to the lack of a practical shear-strengthening system. To address this concern, an innovative shear-strengthening system using prestressed carbon-FRP (CFRP) sheets was developed in this study, which can conveniently anchor the CFRP sheets and apply prestress to them. Undamaged and damaged rectangular RC beams were strengthened and tested to verify the feasibility and effectiveness of this system. The test parameters included the prestressing level, initial damage, and CFRP reinforcement ratio. The experimental results showed that using developed prestressed CFRP shear-strengthening system could alter the failure mode from shear to flexure. The prestressed CFRP system could significantly increase the shear capacity, restrain diagonal crack propagation, and improve ductility of RC beams. Compared with the unstrengthened beam, the cracking and ultimate loads of the prestressed CFRP shear-strengthened undamaged beams increased by over 115 % and 75 %, respectively, while those of the non-prestressed CFRP strengthened beams increased by 65 % and 60 %, respectively. Finally, a simplified, design-oriented prediction method was proposed to evaluate the shear resistance of undamaged rectangular RC beams strengthened using anchored prestressed CFRP U-strips. Comparisons between the calculated and the test results demonstrated that this simplified method could well evaluate the shear capacity of the strengthened RC beams.