Seismic performance of severely earthquake‐damaged precast columns repaired under load using prestressed CFRP fabrics

Abstract A repair method using grouting material and prestressed CFRP fabric reinforcement is proposed to ensure that severely damaged Category A buildings (such as hospitals) can continue to function effectively after repair. To evaluate the effectiveness of this method, four precast columns (PC) were designed with variables including longitudinal reinforcement diameter and axial compression ratio. First, pre‐damage pseudo‐static tests were performed on the precast columns, followed by a second seismic performance test on the columns that were repaired under load. By comparing the seismic performance of the columns in the two tests, the seismic performance of severely damaged PC is significantly restored and improved after using this method. For repaired PC with an 18 cm longitudinal bar diameter, the displacement ductility under axial compression ratios of 0.3 and 0.6 was restored to over 92.6% of the undamaged state, with energy dissipation capacity increasing by 58.0% and 32.4%, respectively. For repaired PC with a 22 cm longitudinal bar diameter, the ultimate displacement angles increased by 51.5% and 127.3% under axial compression ratios of 0.3 and 0.6, with energy dissipation capacity increases of 97.1% and 92.5%, respectively. The differences in repair effectiveness can be attributed to the better bond between the small‐diameter longitudinal bars in the precast columns and the concrete, resulting in higher levels of damage in the PC with smaller‐diameter longitudinal bars under the same preloading completion criteria. For the large‐diameter longitudinal bar PC, the repair effectively improved cracks by pre‐damage and the bond failure between the longitudinal bars and concrete, resulting in more significant improvements in seismic performance. Furthermore, a concrete strength calculation method for repairing severely earthquake‐damaged PC with prestressed CFRP fabric under load is proposed. It defines a strength reduction factor as the ratio of the repaired PC strength to that of the undamaged PC, with the reduction factor ranging from 0.88 to 0.97.