Combined mechanical anchorage and composite materials for strengthening reinforced concrete beams with defects: an experimental study on capacity and ductility

This study proposes a novel strengthening method for reinforced concrete beams, especially for defective beams, and evaluates the effectiveness of the method through four-point bending tests conducted on two control beams, four strengthened intact beams, and twelve strengthened beams with initial defects. The proposed method utilises a fabric-reinforced cementitious matrix and hybrid fibre-reinforced polymer (FRCM-HFRP) composite system combined with additional anchorage to enhance both the capacity and ductility. The failure analysis confirmed the synergistic effect of the bottom fabric-reinforced cementitious matrix (FRCM) and lateral confinement engineered cementitious composite (ECC) layer effectively suppressing diagonal shear crack propagation and improving plastic performance. Additionally, the incorporation of nail anchorage further prevented debonding of the bottom strengthening layer. The experimental results demonstrated that applying FRCM at the bottom not only synergizes with glass-fibre-reinforced polymer (GFRP) sheet to mitigate stress concentration in carbon-fibre-reinforced polymer (CFRP) sheet but also enhances the load-carrying capacity and deformation capacity of the structure. Furthermore, fully arranged nail anchorage improved composite action, mitigating stress concentration in CFRP sheets and increasing the overall ductility and material utilisation efficiency of the strengthening system.