DESIGNING. 183 



bursting stresses greater than those in the sides of the tank in 

 the ratio 77^, where is the angle which an element of the 



cone makes with a horizontal line. I am unable to tell exactly 

 what was in the case of the Fairhaven tank from any published 

 data, but presume that it was in the neighborhood of 45. If 

 equals 45, the upper ring of plates in the conical bottom was 

 overstressed about 40% beyond what good practice would 

 indicate as reliable. In addition comes the stress over each post 

 due to the fact that the circular girder was made in segments 

 instead of continuous. 



*' Under the circumstances indicated above the writer does 

 not consider the failure of the tank a matter for surprise. It 

 may readily have happened that the lower flange of the circular 

 girder, after having been repeatedly stressed beyond the elastic 

 limit, may have bent inward at some post. The result would be 

 a redistribution of the stress which would be pretty sure to tear 

 the tank at its weakest point, which in this case was the conical 

 bottom. The first indication of failure visible from the ground 

 would be a stream of water escaping from this tear, which would 

 be immediately followed by the collapse of the structure. The 

 writer considers this the most probable way in which the failure 

 occurred, but if for some unknown reason the bottom disrupted 

 first, the fact that the circular girder was in unstable equilibrium, 

 so to speak, would lead to the immediate collapse of the structure. 

 The writer considers that the lessons to be drawn from the failure 

 are that in the design of elevated steel tanks: 



" i. A larger factor of safety should be used for the curved 

 bottom than for the vertical sides of the tank. 



" 2. The lower portions of the vertical sides of the tank should 

 be strengthened to resist the shearing and other girder stresses 

 caused in them by transferring the load to the posts. 



"3. The junction of the bottom and sides of the tank should 

 be held true tc shape and the radial components of the post 



