This paper studies the effects of varying amounts of non prestressed reinforcement on the stress in unbonded prestressing tendons at flexural strength in partially prestressed concrete beams. The study was both experimental and analytical in scope. Altogether, twenty-two unbonded and four bonded partially prestressed concrete beams were tested. Test results show that the stress in unbonded tendons at flexural strength is a function of the reinforcement indices of both the unbonded tendons and the bonded nonprestressed reinforcement. The analytical data agree closely with the experimental results. An empirical equation is included to estimate the ultimate stress in unbonded tendons.
