(1) Friction coefficient: where F is the force measured by the anti-slip test to cause the initial slip of the test piece, and nf is the number of friction faces, which is the sum of the measured values ​​of the high-strength bolt tightening pre-tension corresponding to F. (2) Torque factor: where d is the nominal diameter of the high-strength bolt (mm), M is the applied torque value (N.M), and P is the bolt pre-tightening force. The 10.9 high-strength large hex bolt connection must ensure that the average value of the torque coefficient K is 0.110~0.150. The standard deviation should be less than or equal to 0.010.
(3) Initial tightening torque: In order to reduce the influence of steel plate deformation during bolt tightening, secondary tightening can be used to reduce the mutual influence between successive tightening bolts. The high-strength bolt is first twisted for the first time, so that the axial force should reach 60%-80% of the standard axial force.
(4) Final tightening torque: The torque for the final tightening of the high-strength bolt is the final tightening torque. Considering the loss of various prestressing forces, the final tightening torque is generally 5% to 10% greater than the theoretically calculated torque value according to the design pretension.
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