88 TOWERS AND TANKS FOR WATER-WORKS. 



Assuming that the three rods, C, D and E, are in tension 

 and are capable of exerting a holding down value of 87,599 ^ s 

 each, the three would exert an effect equal to approximately 131 

 tons, which would be added to the dead weight and measured 

 along the vertical line G-F, Fig. 9, proving graphically the 

 stability of structure. 



The maximum stress per circumferential inch is the bending 

 moment divided by the area, or, S + M + A-, this value when 

 multiplied by the length of the arc between anchor rods gives 

 the maximum wind-stress on each rod. The net stress is found 

 by dividing the weight of metal by the number of rods and 

 subtracting from the maximum stress, thus S = M + A W + N. 



Hydrostatic Pressure. In addition to the external pres- 

 sure exerted by the wind, stand-pipes are subject to, and must 

 be designed to resist, an internal pressure of water with which 

 they will be filled, or to resist the " Hydrostatic Pressure." 

 From experiment it has been found that the maximum densi- 

 ty of water occurs at from 6 degrees to 7 degrees above freez- 

 ing point, from which point its density decreases and volume 

 increases with each degree of advancing temperature. 



At the level of the sea, the approximate atmospheric pres- 

 sure of 14% Ibs. per sq. in. will balance a column of water 34 

 ft. in height. The weight of water is approximately 62^ Ibs. 

 per cubic foot, and is usually so taken for the purpose of cal- 

 culation. A cubic foot of water, in a cubical receptacle, exerts a 

 pressure over the base of I44sq. inches, equivalent to its weight ; 

 so then, the pressure of 62^ Ibs. of water over 144 sq. inches 

 (TTT) e q ua ls -43357 Ibs. ; hence, to find the pressure of any 

 column of water, multiply the height or "head " in feet by 

 .434; very roughly, divide the given head by 2. 



Conversely, when the pressure per sq. inch is given, to 

 find the head to which the pressure is due, $ equals 2.30677, 

 or roughly, 2.3. The following table may be found useful: 



