At present, the ACI Building Code (ACI 318-77') permits cracking in prestressed concrete members. Cracked members are commonly said to be partially prestressed. The advantages of partial prestressing are numerous and have been given by Abeles, 2 Lin,3 Leonhardt,4 Moustafa,5 Naaman,6 Balaguru,7 and others. Partial prestressing may be achieved by reducing the level of tension in the prestressing tendons, or by combining fully stressed tendons with non-prestressed reinforcement (tendons or bars). Reduced prestress minimizes initial camber and end zone cracking problems. A pretensioned strand stressed at a low level requires relatively small transfer and development lengths. This is particularly beneficial for short members. Also, low prestress produces relatively small initial and creep shortening. This is a better condition at connections whether they are sliding or rigid connections. Other advantages of partial prestressing are improved ductility and energy absorption, which are desirable for earthquake resistant design, reduced demand for high concrete strength at transfer, and possible reduction of overall structural cost.
