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Flexural behaviour of reinforced concrete beams strengthened with pre-stressed and near surface mounted steel–basalt-fibre composite bars

Fibre-reinforced polymer bars have been widely used for strengthening concrete members due to their high strength, light weight and strong corrosion resistance. A near-surface mounted strengthening system has been adopted to protect the fibre-reinforced polymer bars from external hazards. To make up the lower stiffness and ductility of fibre-reinforced polymer bar compared to steel rebar, this study proposed to use a pre-stressed near-surface mounted steel–basalt-fibre-reinforced polymer composite bar. The steel–basalt-fibre-reinforced polymer composite bar is manufactured through wrapping a steel rod by a basalt-fibre-reinforced polymer cover. A total of nine reinforced concrete beams, including one control or calibration and eight others strengthened by pre-stressed near-surface mounted steel–basalt-fibre-reinforced polymer composite bars, are fabricated and tested. Results show that the proposed steel–basalt-fibre-reinforced polymer composite bar strengthening method can improve both the strength and ductility of the reinforced concrete beams. Pre-stressing of the steel–basalt-fibre-reinforced polymer composite bars further increases substantially the beams’ load-carrying capacity by restraining crack propagation in concrete. Standard-based load analysis correctly predicts the cracking load, however, underestimates the ultimate strength of the beams. Finite element method modelling is conducted to provide a more effective load-carrying capacity prediction and a case study is carried out with regard to the amount of the strengthening steel–basalt-fibre-reinforced polymer composite bars.