Q. Determine the Bolt Torque?

The value of the bolt torque, which will give the desired bolt stress, can be calculated from Equation. The friction coefficient (K) is for a well-lubricated bolt and nut.

T = K * S_B * d * A_b

Where :

K = 0.2 (friction coefficient)

T = bolt torque (ft-lbs)

S_B = desired bolt stress (psi)

d = root diameter of the bolt (in).

A_b = cross-section root area of the bolt (in²)

The calculated torque values will generate the approximate stress values (SB). Tests have shown that the average stress will be within 10% of the desired loading stress after step-wise torquing of well-lubricated and undamaged bolts.