Contribution of U-shaped strips to the flexural capacity of low-strength reinforced concrete beams strengthened with carbon fibre composite sheets

This paper presents the results of an experimental study on the flexural behaviour of low-strength reinforced concrete beams strengthened with externally bonded carbon fibre sheets and on the bond behaviour between these sheets and concrete. The applied sheets without additional anchorage always debonded from the surface of the tested specimens. With the help of U-shaped strips applied at the ends of longitudinal sheets, the load bearing capacity and deforming ability of the strengthened beams could be significantly improved. Based on the fracture mechanics model, the effective shear force between these sheets and concrete was determined. According to the brace-arch model and a further parametric study, it was found that the bearing load of a strengthened beam without additional anchorage increased with the concrete strength and that the calculated capacity of a strengthened beam increased with the sectional area of sheets in a more effective rate when U-shaped strips were applied.