ABSTRACT
Prestressed concrete is a compound material which can be made to possess properties ranging from those of a brittle elastic material susceptible to sudden failure to those of a yielding or ductile material. It is possible to design prestressed concrete members in such a way that they exhibit either great flexibility with little permanent deformation, or great rigidity. Flexural cracks may close com pletely when the load is reduced (provided that it does not exceed 70 per cent of the load causing failure), and the outstanding property of prestressed concrete is this recovery of deformation. The versatility of the material is well illustrated by prestressed concrete beams, the behaviour of which depends on the physical properties of the concrete and the steel, the size and shape of the section, the amount of steel, and its distribution in tensile zone of concrete, the magnitude of the prestressing force, and the efficiency of the bond. As such large differences in behaviour are possible, it is important that the load causing cracks, the distribu tion and size of cracks, and the ultimate static, fatigue and impact loads should be carefully considered and the corresponding factors of safety assessed.
