INFLUENCE OF NONPRESTRESSED REINFORCEMENT ON THE STRENGTH OF UNBONDED PARTIALLY PRESTRESSED CONCRETE MEMBERS

An ivestigation of the stress in the prestresing tendons at ultimate in unbonded partially prestressed concrete beams is described with particular emphasis on the effects of nonprestressed bonded reinforcement. Load tests on 6 rectangular section unbonded beams are reported. It is shown that the presence of bonded nonprestressed reinforcement has a marked influence on the flexural behavior of unbonded beams and the related increase of stress in the prestressed steel at ultimate. Test results are compared with predictions from 2 relevant design codes, and some limitations in the application of these codes to unbonded partially prestressed concrete construction are identified.