DESIGNING. 1 89 



support, and are included in the chapter " Stresses in a Steel 

 Water-tower." 



On account of the maximum stress and heavy bending moment 

 over each point of support, it cannot be too strongly insisted 

 upon that prudence demands provision for a continuous curved 

 girder. While it is true that a number of water-towers have 

 been built without the use of the circular girder other than the 

 tank cylinder itself, the only provision being an increase in the 

 thickness of the lower tank ring over that required for hydrostatic 

 stresses, such practice is likely to cause trouble, and a girder 

 should be designed with a web consisting of the lower plate 

 slightly heavier than theoretically determined as necessary, and 

 reenforced with angle stiffeners, and provided with both bottom 

 and top flanges. In discussing the riveted girder, Carnegie's 

 Handbook has this to say: "The web of the girder must be 

 made of such thickness that there will be no tendency to buckle 

 and that the vertical shearing stress per square inch will not 

 exceed 10,000 pounds. 



" This shearing stress is greatest near the supports and is 

 obtained by 'dividing half the load upon the girder (providing the 

 load is symmetrically applied) by the web section. The first 

 condition (security against buckling) is attained when this shear- 

 ing stress does not exceed 



11,000 



ffi 



in which d represents the depth of web in clear of flange of 

 girder, and / the thickness of one web plate in inches. 



" Ordinarily this formula gives a lower stress than 10,000 

 pounds, so that both conditions are usually attained when the 

 first is. Instead of increasing the thickness of the web, it may be 

 stiffened by means of vertical angles riveted to it at proper inter- 



