ABSTRACT
There are significant differences in principle between reinforced concrete and prestressed concrete. In the design of reinforced concrete beams it is assumed that the tensile strength of the concrete is negligible, and the tensile forces created by the bending moments are resisted by reinforcement, to which the forces are transferred by bond. Cracking and, to a large extent, deflections are virtually irrecoverable in ordinary reinforced concrete, with relatively poor bond between the steel and concrete, though with high-strength concrete and good bond a substantial degree of recovery may take place. The reinforcement usually exerts no forces on the member on its own account. In prestressed concrete, on the other hand, the primary purpose of the prestressing steel is to apply a force to the concrete, either by bond or by means of special anchoring devices; hence the whole of the concrete can be made to act structurally. The steel required to produce the prestressing force is thus used actively to preload the member and cracking and deflections are recoverable to a higher degree.
