High-strength bolt is a new type of connection developed in the 1950s. It has many advantages, such as simple construction, good mechanical performance, removable, fatigue resistance and non-loosening under dynamic load. It is a promising connection method.

In assembly, the torque wrench is used to tighten the nut so that the bolt produces a huge and controlled pre-tension Fp. Through the nut and liner, the same pre-pressure Fp is produced for the connector. Under the action of pre-pressure Fp, along the surface of the connector will produce greater friction. Obviously, as long as the sliding force F is less than the friction, the component will not slide and the connector will not be destroyed. This is the principle of high-strength bolted connection.

As mentioned above, high-strength bolted connections rely on the friction between the contact surfaces to prevent them from sliding each other; in order to make the contact surfaces have enough friction, it is necessary to increase the clamping force and increase the friction coefficient between the components. The clamping force between members is achieved by applying pre-tightening force to bolts. However, the pre-tightening force of ordinary bolts made of low-carbon steel is limited because of the material strength limitation. The friction force produced by the pre-tightening force is smaller than that of ordinary bolts. Therefore, if the friction force caused by the pre-tensioning force of bolts is used to transmit the force, the bolts will be used to transfer the force. The strength of the material must be much greater than the strength of the component material, that is, bolts must be made of high-strength steel, which is why high-strength bolted connections.

The strength of the material used for high strength bolts is 4-5 times that of ordinary bolts, and the commonly used performance grades are 8.8 and 10.9. Grade 8.8 adopts high quality carbon steel No. 35 or 45 steel, and 10.9 grade adopts alloy structural steel 20MnTiB, 40B and 35VB. High strength bolts have two types: large six angle bolt and torsion shear type. The specification of steel structure stipulates that the material of high-strength bolts should conform to the current standards.