1 68 TOWERS AND TANKS FOR WATER-WORKS. 



H'B. Thus, where the scale of the base is taken in i6ths, 

 of an inch thickness will be represented by twelve subdivisions, 

 which, multiplied by 66.6 per cent., gives 7.99 as the distance 

 of the point where the rivet-efficiency line cuts the base to the 

 point H'. 



Draw the dotted diagonal H-R. 



For each ring or panel the distance of each vertical dotted 

 line from the dotted diagonal will graphically demonstrate the 

 excess or decreased strength of that particular joint more or 

 less than 66.6 per cent. As in the explanation of the proper 

 relation of plate thickness to the diagonal theoretical line of 

 strength, so the dotted vertical, showing rivet efficiency of 

 the particular vertical joint, should not fall very far on either 

 side of the 66.6 per cent. -rivet-efficiency line in any section or 

 ring; otherwise the joint will be too weak for safety in the one 

 case or unnecessarily strong, entailing increased cost, in the 

 other. 



It has been previously explained how the efficiency of a 

 riveted joint was determined, and from the formula deduced 

 a set of tables has been calculated ; it is therefore only neces- 

 sary to inspect the strength and efficiency of any joint as 

 shown in the table, and to adopt and specify the character of 

 joint, giving the requisite percentage of strength; then for any 

 ring or section whose thickness is known and indicated on the 

 vertical scale, multiply the number of subdivisions represent- 

 ing that thickness by the per-cent. efficiency of the accepted 

 joint, and the result can be used to plot the point where the 

 vertical dotted line should be drawn, as was done to establish 

 the point R on the base-line H'B. 



The strain-sheet given for the 24-ft. X i2O-ft. stand-pipe, 

 and further above explained and described, is frequently more 

 or less elaborated to include other details, and is sometimes 

 so complete as to render further specifications unnecessary for 

 designing. Further details for this stand-pipe are given on 

 the following page : 



