(1) Friction coefficient: where F is the force of the specimen to produce the initial slip measured by the anti-slip test, nf is the number of friction surfaces, and the sum of the measured values of the tightening force of the high strength bolts corresponding to F.
(2) Torque coefficient: where d is the nominal diameter (mm) of high strength bolts, M is the applied torque value (N.M), and P is the bolt preload. 10.9 high-strength large hex bolts must ensure that the torque coefficient K average of 0.110 ~ 0.150. The standard deviation should be less than or equal to 0.010.
(3) the beginning of the torque: In order to reduce the bolts during the process of steel plate deformation, can be used to reduce the second tightening to tighten the interaction between the bolts. High-strength bolts for the first time the first twist, so that the axial force should reach the standard axial force of 60% to 80%.
(4) final torque: high-strength bolts last tightening torque for the final torque. Considering the loss of various prestresses, the final torque is generally 5% to 10% greater than the torque calculated by the design pre-tension.