I/O TOWERS AND TANKS FOR WATER- WORKS. 



Bed-plate and Connections. In calculations for the thick- 

 ness of the *' bed-plate " or the. plate which is to form the bot- 

 tom of the cylindrical stand-pipe, the moment of the weight of 

 the column of water, acting through the centre of gravity 

 and applied at the centre of the circle, would be found by mul- 

 tiplying the weight by its leverage, the radius of the circle, 

 and the thickness of the plate to resist this stress would be 

 found as explained ; but in stand-pipes the bed-plate rests 

 upon and is supported by the subfoundation, so that it is only 

 necessary to provide a plate which can be satisfactorily joined 

 to the shell. In practice where the shell-plate, bottom ring, 

 is in. or over in thickness, the thickness of the bed-plate is 

 assumed at the thickness of the shell ; where the bottom 

 ring is less than 1 in., the bed-plate is taken as the same 

 thickness as the shell. In large stand-pipes the bed-plate 

 sheets are cut economically to represent segments of the circle, 

 are riveted together in the field, and joined to the shell by 

 some form of "angle" or " L" curved to radius. The length 

 of the legs of the angle are determined by the character of 

 riveting required, sometimes it being sufficient to single-rivet 

 both legs to the shell- and bed-plate respectively; sometimes 

 the shell is double- and the bed-plate single-riveted ; some- 

 times both are double-riveted, hence the comparative lengths 

 of the angle-legs. On page 87 it was shown that the maximum 



M 



bending moment per square inch of circumference was S = r, 



A. 



t'.'.en for a tank 24 ft. diameter by 120 ft. in height, and where 

 the dead weight or weight of the metal is roughly 85 tons, 

 M = 6,400X720 = 62, 208,000 pounds-inches. The area A of 

 the tank being 65,144 square inches, the maximum bending 



, 62,208,000 



stress per circumferential inch is ' == 955 which multi- 

 plied by its leverage, 144 inches, gives 165,024, divided by the 

 allowable unit stress of t u e metal, 15,000, gives n as the section 

 modulus, and found from standard section tables to approx- 



