Experimental and Analytical Investigation of Partially Prestressed Concrete Beams Strengthened with Carbon Reinforcement

Experimental behavior of prestressed concrete beams strengthened with carbon sheets and the analytical predictions are reported. Two sets of beams made with normal strength (35 MPa, 5 ksi) and high strength (70 MPa, 10 ksi) concrete were strengthened with two and three layers of carbon sheet reinforcement. The beams were instrumented to measure deflection, and strains in composite, concrete, prestressed steel , and nonprestressed steel, and tested to failure using third point loading over a simply supported span of 3 m (10 ft). The results indicate that prestressed concrete beams can be effectively strengthened with carbon sheets, the loss of ductility was minimal for prestressed concrete beams. A strength increase of 86% was obtained for 3 layers, and the decrease in failure deflection was less than 10%. The authors believe that the stress-strain behavior of a prestressing strand, which has a continuous strain hardening with no yield plateau, is the main reason for this different behavior. The strength capacities can be predicted with good accuracy.