238 TOWERS AND TANK'S FOR WATER-WORKS. 



Since the area of a circle represented by the base, 24 ft. 

 diameter, is 452.4 sq. ft. for ordinary brick masonry whose 

 weight is 1.6 tons per cubic yard, each vertical foot of foun- 

 dation weighs 26.88 tons, therefore ^ = 6 ft. as the 



20.00 



height of the substructure. 



As has been explained, the anchorage consists usually of 

 iron or steel rods set in the masonry and bolted to some 

 external shapes riveted to the superstructure. Such rods 

 receive their holding-down or resisting stresses from flat 

 washers supported by the bolt-head of the rod and acting 

 against the masonry above, and must be designed of size and 

 strength sufficient to prevent their being bent downward or 

 broken off, and with a surface sufficiently broad to prevent 

 the masonry from giving way, thereby permitting the washer 

 and bolt to crush the masonry and pull through, and their 

 bearing-area must therefore be such as to distribute the ap- 

 plied load over a sufficient portion of the masonry to prevent 

 overloading and crushing. 



If ten rods and washers were provided as anchorage and 

 with a leverage of 12.5 ft., each rod would bear ^ of the 

 total applied stress, in this case -jL- of 1632, or 163.2 ft. -tons, 

 and this divided by their leverage, 12.5 ft., each rod and 

 washer must be designed to resist 13 tons pressure, or a total 

 stress of 26,000 Ibs. 



Such washers are usually of cast iron with a unit maxi- 

 mum shear value of 20,000 Ibs. per sq. in. 



The safe bearing-value of masonry as taken from the 

 table being approximately 10 tons per sq. ft. or 144 sq. 

 in., for brick, the area of the washer to resist the applied 



stress would be - , or 187.2 sq. in. ; and if a circular 



washer were used, its diameter would be about 15 to 16 in. 

 and the unit-stress 140 Ibs. per sq. in. over the surface. The 



