1 84 TOWERS AND TANKS FOR WATER-WORKS. 



thrusts should be provided for by a circular girder extending 

 entirely around the tank and having its web system horizontal. 



" 4. A balcony should be provided at the junction of the bottom 

 and sides of the tank, to permit ready inspection of this most 

 important part of the structure. 



" The writer will add that it is very important that the 

 loads should bear centrally on the posts, or that the stresses due 

 to eccentricity of loading should be amply provided for." 



Consideration of Tank Bottom and Connections. During 

 the prolonged discussion of the Fairhaven failure Prof. A. Mars- 

 ton again contributed a short article with details of a full hemi- 

 spherical tank bottom and connections, which was published in 

 the Engineering News of January, 1902, and this design is re- 

 produced here as Fig. 51. 



In the article alluded to, Prof. Marston expresses his decided 

 preference for this type rather than either the segmental or conical 

 bottom, urging that the latter introduces a radial inward pull 

 on the joint, liable to cause trouble. It was also pointed out 

 that the stresses in a hemispherical bottom are only one-half, 

 while those developed in the conical bottom are larger than 

 those in the vertical sides of the tank ; therefore, by using for the 

 bottom the same thickness cf plate as theoretically determined 

 for the shell, the hemispherical bottom would develop a factor 

 of safety twice that provided for the vertical sides. 



In the consideration of this type entirely in its commercial 

 and practical aspect, an expression was asked of a representative 

 of one of the great bridge companies, himself an expert in the 

 design and construction of such structures, and who replied in 

 part as follows: "The objection to the hemispherical bottom 

 from the manufacturer's point of view is not nearly so strong as 

 it was a few years ago, and there is now no difficulty in getting 

 competitive bids on the manufacture of the spherical bottom. 

 The additional costs of labor required for manufacturing spherical 

 bottoms are usually more than offset by the saving of material 



