(1) torque method

According to the relationship that torque M is proportional to pre-tension, the nuts are initially tightened with a common wrench, and then the special wrench which can display the torque value is used to tighten the nuts to the prescribed torque value.

(2) corner method

A method for determining the rotation angle of the nut in direct proportion to the pre-tension of the bolt after close contact between the plates.

When fastening, screw the nut to the non-rotating position with a short wrench, and then screw the nut to the prescribed position with a long wrench to achieve pre-tension.

(3) break the bolt tail.

It is used for twisting shear type high strength bolts. This bolt has a tailored tail. When fastening, use a special spanner glove to hold the bolt and bolt tail, one sleeve is turning forward, the other sleeve is reversing, when the nut is tightened to a certain extent, the bolt tail is screwed off. Since the groove depth of the bolt tail is determined by the relationship between the torque and the pre-tension, the corresponding pre-tension force is reached when the bolt is screwed off.

In the high-strength bolt connection, the friction coefficient has great influence on the bearing capacity. The test results show that the friction coefficient is directly related to the material quality of the component, the roughness of the contact surface and the magnitude of the reverse force, among which the form of the contact surface and the material quality of the component are the main factors. In order to increase the friction coefficient of the contact surface, the contact surface of the components within the connection area should be treated during construction, such as sandblasting, cleaning with steel wire brush, etc. In the design, according to the engineering situation, the method of bigger friction coefficient should be adopted as far as possible, and it should be clearly indicated on the construction drawing.