(1) Friction coefficient: where F is the force that causes the initial slip of the specimen measured by the anti-slip test, and nf is the number of friction surfaces, which is the sum of the measured values of the high-strength bolt tightening pretension force corresponding to F.
(2) Torque coefficient: 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 preload. The 10.9 grade high-strength large hexagon bolt connection must ensure that the average value of the torque coefficient K is 0.110~0.150. Its 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 in the bolt tightening process, secondary tightening can be used to reduce the mutual influence between successive tightening bolts. The first screwing of high-strength bolts is the initial screwing, so that the axial force should reach 60%~80% of the standard axial force.
(4) Final tightening torque: The torque used for the final tightening of high-strength bolts is the final tightening torque. Considering the loss of various prestresses, the final torque is generally 5%~10% larger than the torque value calculated theoretically according to the design pretension.
Introduction to steel structure – anti-corrosion measures for steel structure
