194 



TOWERS AND TANKS FOR WATER-WORKS. 



The tendency toward standardizing is undoubtedly account- 

 able for the facts presented. 



In designing a girder capable of safely carrying all the im- 

 posed stresses, a reduction of the length of span and consequent 

 decrease cf the size and weight of the members of the circular 

 girder may be accomplished by increasing the number of sup- 

 porting columns; or the length of span may be reduced by de- 

 signing short diagonal struts, usually two for each column, 

 reducing the length of span in accordance with the number of 



FIG. 53. 



struts supplied, two such struts to each column of a four-column 

 tower giving twelve bearing points instead of four along the 

 curved girder; but this method of reducing the length of un- 

 supported span is open to objection on account of the eccen- 

 tricity of loading and the multiplication of members and joints. 

 The usual four-, six-, and eight-column towers being made 

 up of certain standard shapes, is laid out and riveted together 

 at the shop, and the lengths so constructed are carefully marked, 



