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Update time : 2015-03-11 21:17:08
High Strength Bolts are generally used to connect the main components of building structures. Common bolts can be reused, and high-strength bolts can not be reused. High strength bolts are generally used for permanent connections.
The high-strength bolt is a heavy bolt. The friction type uses a torque spanner to apply the high strength, and the pressure type screws off the hex head. Ordinary bolts have poor shear resistance, which can be used in secondary structure. Ordinary bolts only need to be tightened.
Ordinary bolts are generally 4.4, 4.8, 5.6 and 6.8. High strength bolts are generally grade 8.8 and grade 10.9, most of which are grade 10.9.
Level 8.8 and 8.8s are the same. The mechanical properties and calculation methods of common bolts and high-strength bolts are different. The stress of high-strength bolt is to bear the external load by applying pretension P in its interior, and then producing friction resistance on the contact surface between the connected parts, while the ordinary bolt bears the external load directly.
More specifically:
High strength bolt connection has the advantages of simple construction, good mechanical performance, detachable and replaceable, fatigue resistance, and no looseness under dynamic load. It is a very promising connection method.
The high-strength bolt is to tighten the nut with a special spanner, so that the bolt produces a huge and controlled pretension. Through the nut and the base plate, the same amount of preload is generated on the connected parts. Under the pre pressure, there will be great friction along the surface of the connected parts. Obviously, as long as the axial force is less than this friction, the components will not slide and the connection will not be damaged. This is the principle of high-strength bolt connection.
High strength bolt connection relies on the friction between the contact surfaces of the connectors to prevent them from sliding. In order to make the contact surfaces have enough friction, it is necessary to increase the clamping force and the friction coefficient of the contact surfaces of the components. The clamping force between components is achieved by applying pretension to the bolt, so the bolt must be made of high-strength steel, which is called high-strength bolt connection.
In the high strength bolt connection, the friction coefficient has a great influence on the bearing capacity. The test shows that the friction coefficient is mainly affected by the form of contact surface and the material of components. In order to increase the friction coefficient of the contact surface, sand blasting and wire brush cleaning are often used to treat the contact surface of components within the connection range.

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