18 PROBLEMS IN STRENGTH OF MATERIALS 



> 



p 



then = factor of safety against tearing the plate, 



p 



= factor of safety against compressing the rivets, 



p 



= factor of safety against shearing the rivets. 



DESIGN OF RIVETED JOINTS 



If no other consideration than economy of material in securing 

 the necessary strength were taken into account in designing a joint, 

 the relations between t, d, and p ought to be selected so as to make 

 the values of P t , P,, and P c equal; the efficiency will then be a 

 maximum. 



The process would be to first compute d by setting P s = P c , and 

 then find p by putting P t = P c . 



Practical considerations, however, such as the stanchness required 

 in some joints, convenience of construction, economy of labor, etc., 

 have led to a diversity of custom in proportioning joints so that they 

 may be best adapted to the particular conditions of use. 



For present purposes it may be assumed that in good American 

 practice in the design of the joints of steam boiler shells, the diameter 

 of the rivet hole is arbitrarily selected, and corresponds, practically, 

 to a value derived from the expression d = K^/t, in which K= 1.5 

 for single and double lap joints, and K = 1.3 for double-strap butt 

 joints. The dimension p is then computed by using the value of d 

 thus determined, and putting P t =P s , or P t = P c , selecting the smaller 

 value of p thus derived as giving the safe dimensions for the pitch. 

 The efficiency of the joint, if otherwise properly proportioned, will be 

 p d 



P 



In staggered double-riveted joints the distance between the two 

 rows of holes should be determined by making the diagonal pitch p" 

 (see Figs. 5 and 8), such that p" d = 0.6 (p d). Experiment has 

 shown this proportion to be a good one. 



For an example we will design a triple-riveted, two-strap butt joint 

 for |-inch plates (Fig. 9). 



