Load Distribution in High Arch Dams

Every year the construction of arch dams involves a great expenditure of money, but methods of design generally adopted in the past have not made full use of the strength of the materials involved. Any method of design that will enable the material to be utilized more effectively, therefore, will effect large savings and increase the confidence placed in this type of structure. A prerequisite to successful design is an exact knowledge of the various forces acting on and in the dam, and the present contribution discusses the principles and methods by which such knowledge may be obtained.On account of the complexity of the factors involved, previous methods of load analysis were based on m any assumptions which aimed at reducing these factors to a form susceptible to mathematical treatment. The principal assumptions are herein reviewed, particularly those relating to the so-called cantilever action. The assumption most strongly attacked is that which regards the arch as being uniformly loaded, and a powerful method of correctly determining the actual non-uniform beam and arch loading is explained.The methods proposed are based primarily on beam and arch deflections and by means of charts and simplified procedure the application of these methods is made comparatively simple and accurate, and dependent on the minimum number of arbitrary assumptions. When the actual loading on beams and arches under any given set of conditions is known, the resultant stresses may readily be determined, and such modifications in design may be made as are required to enable the dam to carry the load most effectively. The lines along which improvements in design may be made, are then suggested.A satisfactory method of arch dam design requires a more complete knowledge of actual temperature variations in concrete, of its elastic properties, and of the effect on the darn of the elastic properties of the foundation rock. Such knowledge will be obtained mainly from measurements and observations on existing dams. Apart from the incompletely known effect of these factors, arbitrary assumptions in the past have led to errors and should be avoided.