Question

A double riveted double strap butt joint is made with 15 mm thick plates and 20 mm diameter of rivets. The pitch of the joints is 90 mm. Allowable stresses are ${\sigma }_t=115$ MPa, $\tau =90$ MPa & ${\sigma }_c$ = 160 MPa.
Calculate the efficiency of the joint.

• A. 56 %
• B. 62 %
• C. 76 %
• D. 68 %

Answer 1

The correct option is B 62 %

d = 20 mm, t = 15 mm,

Pitch 'p' = 90 mm, ${\sigma }_t$ = 115 MPa,

$\tau$ = 90 MPa, ${\sigma }_c$ = 160 MPa

(I) Tearing resistance of plate pitch length

$P_t=(p-d)\times t\times {\sigma }_t=(90-20)\times 15\times 115=120750N$

(II) Shearing resistance of the rivets

Since the joint is double riveted butt joint, therefore the strength of two rivets in double shear are taken

Shearing resistance of the rivets

$P_s=2\times 2\times \frac{\pi }{4}\times \left({20}^2\right)\times 90=113097.33N$

(III) Crushing resistance of the rivets

Since the joint is double riveted therefore the strength of two rivets are taken crushing resistance

$P_c=N\times d\times t\times {\sigma }_c{P}_c=2\times 20\times 15\times 160=96,000N$

Strength of unriveted solid plate

$P=p\times t\times {\sigma }_t=90\times 15\times 115=155,250N$

Efficiency of the Joint

$=\frac{\text{Least of}{P}_t,P_s\text{and}{P}_c}{P}$

$=\frac{96,000}{155,250}=61.8$% $\approx$ 62%