2IO TOWERS AND TANKS FOR WAITER-WORKS. 



This stress is considerable in large structures such as stand- 

 pipes of considerable dimensions, but in the usual water-tower 

 it need hardly be considered. With the 2oX42-ft. tank under 

 consideration, this stress is less than 500 Ibs. per square inch 

 of metal. 



Torsion Moment. The maximum torsion moment of the 

 girder for 4 points of support is found to occur at an angular 

 distance of 19 12' from the point of support, or in the case under 

 consideration, 3.35 feet along the girder, and this stress can be 

 determined from the formula given, viz., o.oo^^Wr. Ordinarily 

 this stress need not be considered for tanks of the usual 

 capacities. 



Horizontal Reaction at the Top of Posts. The total weight 

 being estimated as 958,000 Ibs., the vertical load, W, at each point 

 of support of a four-column tower is 239,500 Ibs., and where the 

 angle of inclination of the post is 6 = j 59', whose tangent is 

 0.14, the horizontal reaction H, according to the formula given 

 = W tan or 33,530 Ibs. 



As with the gravity load, there is also a horizontal reaction 

 from the assumed wind stress, found by graphical analysis (Fig. 

 59) to.be 7468 Ibs., or a total horizontal thrust at the top of each 

 post of 40,998 Ibs.; where r=i2O inches, from the formula and 

 table, the maximum bending moment at each point of support 

 is M=FO.i37, .#> = 674,000 inch-pounds, and to resist which 

 the ring forming the horizontal flange of the circular girder may 

 be used. Its elements, from the details of Fig. 57, are found 

 to be, moment of inertia," 75 = 3847; distance from neutral axis, 

 = 4.03 inches, and modulus of rupture, .# = 954.5. Assuming 

 a unit stress 5, the safe resistance moment of the shape, 

 =.-RXS = 954,500 inch-pounds as against a maximum bending 

 moment found to be 674,000 inch-pounds; hence the flange ring 

 as designed is well within the limit of safety to resist this reac- 

 tion. In large structures, however, where the posts have con- 

 siderable inclination, the flange ring is often found insufficient 



