This study describes a nonlinear analysis for externally prestressed structures. The mechanical behavior of prestressed concrete beams with externally unbonded tendon is defferent from that of normally bonded PSC beams in that the slip of tendons at deviators and the change of tendon eccentricity occurs as external loads are applied in external unbonded PSC beams. The model used in this study is capable of simulating the slip of the tendon at the deviator, the friction at the interface of the tendon and deviator, and time dependent effects such as creep and relaxation. The analyis includes the effects of tension stiffening, and geometric and material nonlinearities. The proposed numerical method was verified by comparision with experimental test data. A parametric study was undertaken to evalulate the behavior of PSC beams either designed using external prestressing or strenthening by it. The study accounted for friction and slip of external tendons at deviators, a number of deviators, variation of tendon profile with applied load, and time dependent effects. The analytical results demonstrated that the slip of tendon at deviator causes decreasing the ultimate strength of the PSC beam, with increasing the number of deviator the prestressed concrete with externally unbonded tendon not slipping tend to the behavior of normally bonded PSC beams, and loading type and position is the main factor to determine the tendon profile.
