Experimental and Theoretical Investigation of Bending in Concrete Beams Strengthened with External Prestressing CFRP Tendons

The flexural properties of concrete beams strengthened by external prestressing carbon fibre-reinforced plastic (CFRP) tendons are studied through static loading tests. The loading processes, failure modes, right-sectional strain features, and ductility of the strengthened concrete beams are analysed, permitting comparisons of the influences of the bending angle of the external CFRP tendons, the strength grade of the concrete, the reinforcement ratio of the internal non-prestressing steel, and the loading strengthening level of the external prestressing CFRP tendons on the flexural properties of the beams. Test results show that the external prestressing CFRP tendons can improve the anti-cracking properties, stiffness, and flexural properties of concrete beams. The bending angle of the external CFRP tendons should not exceed 10°, while the reinforcement ratio and loading strength have obvious effects on the flexural properties of the beams they reinforce; conversely, the strength grade of the concrete has relatively little influence on the flexural properties. Based on the results, a bending bearing capacity formula for concrete beams strengthened with external prestressing CFRP tendons is determined according to the design theory of externally prestressed concrete structures; this formula provides the accuracy required for construction and therefore it can be used as a reference for practical engineering.