ABSTRACT
It is obvious that the accuracy and quality of a design are determined by the accuracy of the basic data; care should be taken to see that these conform as closely as possible to the actual conditions of manufacture and construction, and that any reasonable divergence between the actual and assumed conditions can lead only to a safer structure (that is, the design assumptions should always be on the safe side). This accuracy is in no way improved by excessive arithmetical precision. The loading and bending moments used in design are often conven tional; in assessing the losses it is therefore desirable to consider whether a more probable distribution of load would lead to increased losses. The permissible stresses should be selected in accordance with the principles described in Chapter 5; where any doubt exists as to actual conditions conservative values should be chosen. The same principle should be applied when estimating the losses; they should give the maximum probable prestressing force at transfer and the minimum probable at working load. It is also necessary on occasion to investigate the stresses when minimum losses are assumed to occur.
