Crack characteristics and damage degree of pre-damaged RC beams strengthened with CFRP under various multiple impact conditions

This study aims to investigate the crack characteristics and damage degree of pre-damaged RC beams strengthened with CFRP under various multiple impact conditions. RC beams strengthened with CFRP (ultimate tensile strength 3585.6 MPa) were subjected to drop-weight tests at multiple impact velocities of 5.2 m/s, 4.4 m/s, and 4.4 m/s, respectively. The crack propagation behaviors of all specimens were quantitatively analyzed under multiple impacts. The optimal scheme was determined by comparing the impact force histories of pre-damaged beams with various strengthening methods. Subsequently, with a numerical model established in LS-DYNA program, the influences of hammer mass and impact velocity on the multiple impact behavior of pre-damaged beam with U-wrapping CFRP were further investigated. The results indicated more obvious oblique cracks are observed in pre-damage RC beam. Pre-damage accelerated the beneficial effect of CFRP in preventing and delaying the occurrence of cracks. After three impacts, the maximum oblique crack width and vertical crack width of U-wrapping CFRP pre-damaged beam (DR-U) is the smallest, and the average crack spacing exhibits a reduced trend with an increasing number of impacts. Based on experimental results, the numerical model of DR-U was established under various multiple impact conditions, including different hammer masses and first impact velocities. The displacement recovery coefficient presents a decreasing trend with the increase of hammer mass. Generally speaking, when the first impact velocity >5.9 m/s, the impact resistance of pre-damaged beam with U-wrapping CFRP decreases significantly under multiple impacts. The evolution of various damage area ratio is quantitatively characterized in this paper.