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SIMPLE STRAINS AND STRESSES 73 
by equating the resistance to crushing to either the resistance to tearing 
or the resistance to shearing. 
The ratio of the strength of a riveted joint to the strength of the solid 
is called the efficiency of the joint, The efficiency is called either 
the tearing, the shearing, or the crushing efficiency, according to the kind 
of resistance which is taken as the strength of the joint. The resistance 
of the solid plate being pt/,, the various efficiencies for a double riveted lap 
joint are : ene pod 
Tearing efficiency = ar aig 
Shearing efficiency =o ‘ 
Crushing efficiency = oe = a : 
It is usual to express the efficiencies as percentages by multiplying 
the above by 100. 
The lowest efficiency is the real efficiency of the joint. 
To resist the rupture of the plate between its edge and the rivets, 
as shown at (c), Fig. 82, it has been found by experiment that if the 
least distance between the edge of the plate and the nearest rivet is 
equal to the diameter of the rivet this is sufficient, and this is the rule 
followed in practice. 
For simple lap joints other than the double riveted joint which has 
been considered, the multiplier 2 which was used in the expressions for 
the resistance to shearing and the resistance to crushing must be changed 
to n, where n denotes the number of rows of rivets in the joint. 
The determination of the strength and proportions of riveted joints 
other than simple lap joints presents no particular difficulty, but a few 
cases will now be considered briefly. 
Fig. 83 shows an ordinary double riveted butt joint with two cover 
straps. Considering a strip of the joint equal 
in width to the pitch p, and using the same 
notation as before. 
Resistance to tearing =(p-—d)tf,. . + (1) 
4 * - shearing =4°/, x 2 x 2 . (2) \ 
Fs » crushing=dif,x2 . . . (3) 
Equating (2) to(3)d=@ . . . (4) 
whe Fia. 83. 
: a4 3h | , He 
Equating (1) to(3) and substituting from (4) p= sil 1 + F ). 
If d is given, or fixed empirically, equate (1) to (2), then 
rd*f, 
B= if, +d, 
df, 
and equating (2) to(3) f= "y,' 
