120 



TOWERS AND TANKS FOR WATER-WORKS. 



As it is easier in construction to provide for the tension, it seems 



advisable to make the value of = or<2. When the bottom 



r z 



is a hemisphere =i, that is, r = r y 

 r s 



If r z is made very small in comparison with r, there are un- 

 doubtedly bending stresses in the plate. The amount of these 

 stresses cannot be determined readily, consequently they should 

 be avoided. 



It will generally be most satisfactory to use the hemispherical 

 bottom, as all stresses will then be determinate. Such bottoms 

 can now be manufactured without undue expense. 



Stresses in the Circular Girder.^The circular girder sustains 

 the vertical component just determined plus the weight of the 

 steel cylinder, the tank roof, and its own weight. That is, it 



supports the whole weight of the tank, the contents of the tank, 

 and itself. This load is uniformly distributed along the girder. 



