Example 3: A double riveted double cover butt joint in plates 20 mm thick is made with 25 mm diameter rivets at 100 mm pitch. The permissible stresses are: σ₁ = 120 MPa; t = 100 MPa; σ = 150 Mpa Find the efficiency of joint, taking the strength of the rivet in double shear as twice than that of single shear.