DESIGNING. 185 



and freight. It seems to me good policy to advocate that form 

 of bottom which gives definite stresses, even though that form 

 of construction may cost more in some cases. 



" The plates of the spherical bottom should be made about 1/16 

 of an inch thicker than the figured thickness, to make allowance 

 for the stretching of the plates in shaping them and to give pro- 

 tection against masses of falling ice. 



" Similarly the connection of the bottom to the cylinder should 

 be made stronger than the figured stresses required. 



" Whether the conical or hemispherical bottom is used, I would 

 prefer to connect same to the bottom of the tank cylinder so 

 that the metal forming the joint is a part of the bottom of the 

 circular girder. 



" The post connection is not so easy to make, but it can be 

 satisfactorily solved. The design for the water-tower for the 

 Iowa State College, at Ames, Iowa, published in recent editions 

 of Johnson's ' Framed Structures ' gives a satisfactory solution 

 of this connection. This structure was designed by Prof. A. 

 Marston (Figs. 51-52). 



The detail which shows the posts riveted direct to the tank 

 shell has proved very satisfactory, as it gives a rigid connection. 

 However, care must be taken that the centre of gravity of the 

 connection falls on the axis of the column. Theoretically the 

 curved girder in the horizontal plane which resists the horizontal 

 thrust at the top of the posts should be at this centre of gravity. 

 Practically it is more convenient to place it on a level with the 

 junction of the bottom and cylinder. This arrangement produces 

 some bending stresses in the post and its connections, but ordi- 

 narily they will not be serious." 



In bottoms and connections of this type especial care should 

 be taken in the matter of "laying out" and shop- work, and it 

 has been suggested that for the joint between the sides and bottom 

 the pieces should be assembled at the shop and rivet-holes reamed 

 through; also that adjacent pieces of the bottom-should be fastened 



