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TOWERS AND TANKS FOR WATER-WORK'S. 



.^-Stiffening Girder 



As has been said, at the top of the tank the strain from the 

 water is zero, and considering the cylinder as a stack under 

 wind-pressure the vertical components of the uplift may be 

 regarded as negligible, and there remains principally the con- 

 sideration of the wind normal to the tank, which force probably 

 exercises also a torsion movement and is also known to produce 

 a vacuum within the cylinder and on the leaward side of the 

 structure, for which reasons the stresses are generally considered 

 as indeterminate, nor is it possible with certainty to assume tru 

 resistance offered by the shape, which is probably somewhere 

 between the arch and beam action. 



Th? effect of these stresses is graphically shown on page 28 



in the wreck of the Lincoln, Neb., 

 stand-pipe, whose top angle was 

 broken and the shell plates were 

 crumpled up for some 40 feet below 

 the top, and from which the necessity 

 for making suitable provision for 

 wind- pressure is obvious. 



In general practice a lo-ft. 

 diameter tank should be provided 

 with an angle not less than 4 in. X4 in.; a 20-ft. diameter tank 

 with 6 in. x6 in. angle, and for pipes of larger diameter some 

 f ^rm of stiffening girder, and which might also be utilized as i 

 part of an ornamental design, should be introduced. 



This style of finish for the top of a stand-pipe, while in 

 general use, is subject to criticism in that it is uncovered, 

 and in some waters the sunlight quickly forms organic growths, 

 while the angle without the cresting is an inviting roosting- 

 place for birds the writer having seen dozens of buzzards 

 roosting upon the tops of stand-pipes so constructed; again, 

 in cold climates an uncovered surface is objectionable on 

 account of the greater tendency of the water to freezing, sev- 

 eral recorded failures being ascribed in part to this cause. 



