. Canadian engineer. of taking Poissons ratio into consideration whciattemping to find the actual stresses in a dam body.—Proceed-ings of the Institute of Civil Engineers, igoc). Page 51. 3^0 THE CANADIAN ENGINEER Volume 30. The initial axial compression holds in equilibrium thestresses due to 42 5 per cent, of the total head at thebottom, the remaining 575 per cent, of the load willdivide between cantilever arch and curved beam action inproportion to their relative carrying capacity. By analyzing: (6) it is seen that by simply varying t orRa, or both, the designer can utilize more or less of
. Canadian engineer. of taking Poissons ratio into consideration whciattemping to find the actual stresses in a dam body.—Proceed-ings of the Institute of Civil Engineers, igoc). Page 51. 3^0 THE CANADIAN ENGINEER Volume 30. The initial axial compression holds in equilibrium thestresses due to 42 5 per cent, of the total head at thebottom, the remaining 575 per cent, of the load willdivide between cantilever arch and curved beam action inproportion to their relative carrying capacity. By analyzing: (6) it is seen that by simply varying t orRa, or both, the designer can utilize more or less of theinitial stress to carry the load. If the base thickness inFig. 3 is increased from 70 feet to 110 feet and the thick-ness increased correspondingly at higher elevations, theinitial stresses will be able to support at the foundation 0-4 X H X ? = 0585 X H, or 58 5 per cent, of the 75total water pressure before any shortening in the length of the arch occurs and before additional axial compressionis Fig. 4. When the arch, however, becomes very thick in com-parison with its length, the load is carried more by curvedbeam action than by ordinary arch action. The dam shown in Fig. 3 was designed with varyingradii to keep the central angle of the arch as nearly con-stant as possible at all elevations. For comparison, asection is shown in Fig. 4, using the same unit compres-sion except where the section is wider than a gravitysection near the foundation and the same upstream facebatter, but a single common centre as ordinarily used forboth upstream and downstream faces. For this sectionthe length of the upstream radius is also variable, but itincreases towards the bottom and reaches here a value of322 feet. (See tables of lengths. Figs. 3 and 4.) Theinitial stresses in this dam will resist 20% of the head ofthe water at the bottom. It is, therefore, easily seen thatthe constant angle arch is much more effective in utilizing the initial stresses to carry the load than
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