Impact Performance of Reinforced-concrete Beam Strengthened by CFRP

The impact performance of reinforced concrete (RC) strengthened by carbon-fiber-reinforced polymer (CFRP) was investigated. An impact test was conducted on six simply supported RC beams using a drop hammer testing facility. An explicit numerical simulation was also performed to regenerate the experimental impact process. The time-varying impact force, reaction force, impact displacement, and cracking development were obtained for various test cases. A thorough investigation was conducted on the damage evolution and dynamic stiffness varying process, CFRP working mechanism, displacement restitution, etc. The CFRP fabric peeled off the bottom of the RC beam at midspan, and other parts of the CFRP slipped with concrete under a drop hammer impact load. The test specimen that was stuck with two layers of CFPR separated from the concrete more easily than that stuck with one layer of CFRP strengthening. The RC beam strengthened by CFRP showed few differences in the cracking damage, impact force, impact displacement, and dynamic stiffness compared with the no strengthened beam. A wedge part formed in the midspan of the No. 1 beam under impact loading. The shear-induced oblique crack was clearly reduced for the strengthened RC beam between the midspan and supported position. The restitution coefficient for the impact displacement increased from 0.27 for the non-strengthened beam to more than 0.43 for strengthened ones. The results show that the contribution of CFRP to the flexural capacity of the midspan critical section of the RC beam weakens severely as the CFRP fabric at the midspan peels, which cannot eliminate the impact-induced damage at the impact position during the initial stage. The unseparated CFRP can provide additional shear resistance for the RC beam at the middle and later impact stages. It can also effectively reduce the residual displacement by the elastic restitution effect of CFRP. The increase in the tensional reinforcement ratio can also significantly improve the deformation recovery of RC beams. Three characteristic stages can be classified for the No. 1 RC beam impact deformation, i.e., the elastoplastic deformation stage, stiffness degradation stage, and plastic deformation stage, which exhibit a ductile failure pattern. In contrast, the No. 2 beam has no plastic deformation during the impact process, and brittle failure can be observed. Perfect interfacial bonding performance is vital for improving the impact performance of RC beams strengthened by CFRP. © 2022, Editorial Department of China Journal of Highway and Transport. All right reserved.