ABSTRACT
Various opinions have been expressed on this question. It has been stated, for example, that if the stresses at the working load are within those permitted a sufficient factor of safety against failure is automatically obtained. This is cer tainly true in some cases (for example, under-reinforced members to which large prestressing forces are applied so that the area of steel necessary to provide the prestressing force exceeds that needed for the conditions at ultimate load) but the limited deformation of such a structure may render the design unsuitable. However, when the prestressing force is smaller, additional non-tensioned steel might be required, and in the case of over-reinforced structures the required factor of safety against failure may not be available if elastic conditions only are considered.
