144 TOWERS AND TANKS FOR WATER-WORKS. 



There is no question, however, as to the increased value 

 of a joint made as suggested by Mr. Coffin over the usual 

 method, and it would seem as though the best practice 

 should govern where the whole strength of the structure 

 may depend upon its method of being assembled. 



Efficiency of Riveted Joints. The " efficiency " of a riv- 

 eted joint is described as being the ratio of the strength of the 

 joint to that of the solid plate. Thus, a joint is said to have 

 a /oper-cent. efficiency when the loss of strength, as com- 

 pared with its ultimate strength, is 30 per cent. 



In order to determine the efficiency of a riveted joint, it is 

 necessary to know or to assume the following conditions : 



(i) The tensile strength of the plate. (2) The diameter 

 of the rivets used. (3) The unit resistance of these rivets, 

 and their " pitch " or spacing, taken from centre to centre. 



When proper values have been determined for the forego- 

 ing conditions, it has been found by practical tests and demon- 

 strations that the efficiency of the several joints is approxi- 

 mately as follows : 



Single-riveted joint 56 per cent. eff. 



Double- " " 69 " 



Triple- " " 75 " + " 



Double- welt butt-joint 87 " 



Quadruple-riveted butt-joint. . 95 " " " 



One of the most interesting and practical discussions of the 

 theory and practice of riveting with which the author is 

 familiar, is contained in an address delivered to the students 

 of Cornell College by Mr. J. M. Allen, president of the 

 Hartford Steam Boiler and Insurance Co., and from which is 

 quoted the following: 



Single-riveted Joints (Fig. 40). "In calculating the 

 strength of a single-riveted joint we must know, first, what 

 the tensile strength of the iron or steel plate is, from tensile 



