Abstract: To trace the entire response of unbonded prestressed concrete beams, a finite element model based on the normal plane arc-length algorithm, which can properly deal with the changes of response during loading and is capable of passing the possible limit points prior to the failure of the beams, was developed. Seven unbonded prestressed concrete beams with different amounts of nonprestressed reinforcement were designed, and then analyzed by the proposed numerical model. The analytical results show that the flexural behavior of unbonded prestressed concrete beam without any tensile nonprestressed reinforcement is poor. With a little amount of tensile nonprestressed reinforcement provided, the behavior of the beam can be greatly improved. With the increase of the nonprestressed reinforcement ratio, the cracked stiffness and ultimate load-carrying capacity of unbonded partially prestressed concrete beam increases remarkably, whereas the post-elastic deflection and ultimate stress in tendons decrease notably.