Performance of precracked prestressed beams repaired with CFRP composites under bending loads

Understanding of the efficacy of fibre-reinforced polymer (FRP) composites in repairing precracked concrete beams prestressed with unbonded tendons (UPC beams) is still very limited. The aim of this study was to provide insights into this knowledge gap. The performance of precracked UPC beams repaired with externally bonded (EB) carbon-fibre-reinforced polymer (CFRP) laminates and U-wrapped anchorages was investigated experimentally. The test results indicated that the effect of the EB CFRP repairing systems was significant only after the crack reopening. The EB CFRP system aided in controlling cracks and mitigating the deterioration in beam stiffness. Consequently, the functionality of precracked UPC beams was restored and their performance was significantly improved. Compared with an intact beam (without precracks), the bending crack widths of precracked beams repaired with EB CFRP decreased by up to 61%; moreover, their deformability and ultimate loading resistance increase by up to 22% and 19%, respectively. The U-wrapped anchorages effectively averted the premature EB CFRP debonding and better leveraged the advantages of EB CFRP laminates, thereby increasing the ultimate loading resistance of precracked beams by 24% compared with the intact beam. A calculation method for determining the flexural resistance of precracked UPC beams strengthened with FRP laminates is introduced, considering the impacts of precracking and U-wrapped anchorages.