. Development and electrical distribution of water power . spaced on 6-foot centres, fiveon the upper arm and four on the lower, the arms consisting of 9-inch 13^-pound channels. All portions of the tower are figured to be safe under a windpressure of 30 pounds per square foot on the tower and the wire ofa 700-foot span. The towers will also withstand absolute failureof any single wire, even though none of the resulting strain is trans-mitted to adjacent wires. Fig. 153 illustrates the construction of a standard 60-foottower, which is 12 feet wide and 12 feet across at the base. Theuprights ar
. Development and electrical distribution of water power . spaced on 6-foot centres, fiveon the upper arm and four on the lower, the arms consisting of 9-inch 13^-pound channels. All portions of the tower are figured to be safe under a windpressure of 30 pounds per square foot on the tower and the wire ofa 700-foot span. The towers will also withstand absolute failureof any single wire, even though none of the resulting strain is trans-mitted to adjacent wires. Fig. 153 illustrates the construction of a standard 60-foottower, which is 12 feet wide and 12 feet across at the base. Theuprights are formed of 4-inch angles and the cross-braces of 21-inch, 3-inch, and 3J-inch angles, the diagonal rods being 11-16 300 DEVELOPMENT AND DISTRIBUTION OF WATER POWER inch and § inch in diameter. Four insulators for the telephonelines are mounted on the third cross-bar, 21 feet above the of the towers were made extra heavy for use at points wherethe line changed its direction. The foot-plates of the towers are of cast iron, dipped in asphalt,. Fig. 153.—Standard 6o-foot Steel Tower. and 24 inches in diameter. They are attached at the bottom to4X 4-inch foot posts, which are asphalted on top of the galvaniz-ing. These posts are bolted as extensions to the corner posts ofthe tower, and set in the ground a depth of 6 feet. Tapered holeswere dug for these foot-plates and the earth was tamped back onthem very carefully. No concrete footings were used, except on KERN RIVER PLANT 301 some special work in the city of Los Angeles, where a great manyof the tower heights exceeded 60 feet. The tower parts were madeas light as was consistent with rigid construction. Under the ex-treme conditions mentioned above, the factor of safety in any steelmember is specified to be not less than 2 J. No cast iron was permitted in the construction, except in thefoot-plates. All connections are made with malleable-iron castingswith a factor of safety of 4. The insulator pins are of cast ste
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