Learn about the key points of steel structure installation

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1. Coefficient of friction: , where F is the force measured in the slip resistance test that causes initial sliding of the specimen, nf is the number of friction surfaces, and it is the sum of the measured pre-tightening forces of the high-strength bolts corresponding to F. 2. Torque coefficient: , where d is the nominal diameter of the high-strength bolt in mm, M is the applied torque value in N·m, and P is the bolt preload. For 10.9 grade high-strength large hex bolts, the average value of the torque coefficient K must be maintained between 0.110 and 0.150. Its standard deviation should be less than or equal to 0.010. 3. Initial tightening torque: To minimize the effect of plate deformation during bolt tightening, a second tightening step can be used to reduce the mutual influence between bolts that are tightened one after another. The first tightening of high-strength bolts is called the initial tightening, during which the axial force should reach 60% to 80% of the standard axial force. 3. Final tightening torque: The torque used to finally tighten high-strength bolts is the final tightening torque. Taking into account various losses of prestress, the final tightening torque is generally 5% to 10% higher than the torque value calculated theoretically based on the designed prestress force.