ABSTRACT
Concrete is very strong in compression and very weak in tension. It is thus reinforced by standard steel on the tensile side. To compensate for tensile weakness, another concept developed in the 1920s and 1930s, is that if the tensile region of concrete is pre-stressed in compression prior to imposition of the tensile-causing external forces, the induced tensile stresses will be compensated by the built-in compression stresses within the member. In pre-tensioning method, steel wires, or steel strands consisting of many wires or steel bars, known as tendons, are stressed prior to casting of concrete. The pre-stress is imparted to concrete by the bonding between steel and concrete. In post-tensioning method, the concrete is already set with a duct or sleeve cast into the concrete. Pre-stressed concrete utilizes high-strength concrete and high-strength steel. In addition, ordinary reinforcing steel is also used as shear reinforcement or supplemental reinforcement.
