Ultimate flexural behaviour of externally prestressed new beams and distressed beams

External prestressing has become a popular technique in retrofitting of distressed concrete structures, mainly bridges. It is being successfully used in segmental construction of new bridges, which is evident in metro constructions and other types of bridges. Tendons used in external prestressing are unbonded tendons and therefore they are analytically treated as internal unbonded tendons. Stress at ultimate in unbonded tendons is the parameter used to evaluate the ultimate flexural capacity of a concrete member prestressed with unbonded tendons. As far as new members are concerned, sufficient research works were carried out on predicting the ultimate flexural behavior and developing equations for finding. Therefore, an in depth review has been done on the subject and the behavioural mechanism regarding evaluating ultimate flexural capacity are discussed. As far as distressed concrete members are concerned, an analytical model has been developed for a cracked RC beams strengthened by external prestressing and validated with experimental data, and the results are presented and discussed. The difference in behavior of externally prestressed new beams and distressed beams strengthened by external prestressing are discussed