130 



TOWERS AND TANKS FOR WATER-WORKS. 



Hr r . nHr 



M= [sm cr + sm a"+. . . sm a"] , 



TT 



S = [cos a' + cos a" +... cos a"], 



TT 



C = [sin a' + sin a." + . . . sin a w ], 



w being the number of pairs. 2W equals the number of forces 

 acting, i.e., the number of posts supporting the circular girder. 

 From the above general equations the following table of 

 stresses results: 



STRESSES IN RING AT TOP OF POSTS. 



In the above table H is the horizontal thrust in pounds at 

 the top of each post, and r is the radius of the ring in inches. 



This radius is approximately equal to the radius of the tank 

 cylinder. 



In many cases the ring formed by the bottom flange of the 

 circular girder is not sufficient to resist the stresses resulting 

 from the thrust at the top of the posts, without using a large 

 amount of metal in the ring. This will be the case in large struc- 

 tures when the posts have considerable inclination. In such a 



