16 PROBLEMS IN STRENGTH OF MATERIALS 



(p d) ts t = strength of riveted plate, 



2 tds c compressive strength of rivets, 



70 



2 -- s s shearing strength of rivets. 

 If the joint fail by tearing the plate, efficiency = ; 



2 ds 

 if by the compression of the rivets, efficiency = ; 



P s t 



if by shearing the rivets, efficiency = -- 



pts t 



In a butt joint the main plates do not overlap, but cover plates are 

 used to connect them. When tension is applied to the main plates of 

 a butt joint having two cover plates, one half of this applied tension 

 is transferred to each cover plate. Hence, theoretically, the thickness 

 of each cover plate should be one half that of the main plate ; but 

 the cover plates, or straps, must be thick enough to remain tight 

 against leakage arising from their flexure between the rivets, and so 

 thick that their edges will admit of effective calking. It is customary, 

 therefore, to make the thickness of each cover plate about five eighths 

 that of the main plates. In the case of a single-strap joint, in which 

 the strap is subject to a bending stress as well as to stress from calk- 

 ing, the strap is made 1^ times the thickness of the main plates. 

 Single-strap joints ought not to be used for the seams of boiler shells. 



In a butt joint with single or double riveting, there are twice as 

 many rivet sections to be sheared in a repeating section as in the cor- 

 responding case for a lap joint. Hence the strength of the joint against 

 shearing the rivets is twice as great. The effective rivet-bearing sur- 

 faces in a butt joint are those surfaces only which are in front of the 

 rivets where they pass through the main plate, and their number, 

 therefore, is equal to the number of rivets in one of the. main plates 

 in the repeating section, one surface for each rivet. It must be recog- 

 nized that in butt joints the number of rivets to be considered in a 

 repeating section is the number on one side only of the line of 

 separation of the main plates. Thus, in Figs. 6 and 7, only one 

 rivet can be considered, in Fig. 8 two rivets are taken, and in Fig. 9 

 five rivets. 



