THE FLEXURAL CAPACITY OF CONCRETE BEAMS PRESTRESSED WITH BONDED AND/OR UNBONDED FRP TENDONS

Fiber reinforcement polymer (FRP) has high strength and high stiffness-to-weight ratio, which owns potential to be used as prestressing tendons in corrosive environment. However, concrete beams have showed brittle flexural failure due to the elastic rupture of FRP tendons. In order to improve the ductility, a combination of bonded and/or unbonded prestressing tendons is used. The flexural capacity of concrete beam prestressed with bonded and/or unbonded FRP tendons has been studied theoretically. According to the definition of balanced ratio, the failure modes of concrete beams prestressed with FRP tendons were defined in this paper, and the balanced ratio and the corresponding formula for calculating the flexural strength were derived. In order to verify the correctness of the formula, a series of flexural tests were conducted on 9 concrete beams prestressed with bonded and/or unbonded FRP tendons. The test program validated the proposed method. The results of experiments show that, if the reinforcement of prestressed beam remains the same, the concrete beam prestressed with bonded FRP tendons has the highest carrying capacity, followed by the unbonded prestressed beam, while the external unbonded prestressed beam without deviators has the lowest carrying capacity. Through combination of different FRP tendons, the ductility of concrete beams prestressed with FRP tendons can be improved.