Basic principles of high-strength bolted connections

High-strength bolts are made of high-strength steel plates, or bolts that require a relatively large pre-tightening force, can be called high-strength bolts. High-strength bolts are generally used for the connection of road bridges, railroad tracks, ultra-high pressure and high-pressure machines. The fracture of such bolts is mostly brittle fracture. For high-strength bolts used in high-pressure equipment, in order to ensure the airtightness of the container, relatively large prestressed steel bars must be applied. High-strength bolt connection has the characteristics of simple engineering construction, high bearing capacity, high cost performance, detachable, fatigue resistance, and will not loosen under the influence of dynamic load, etc., and it is still a very promising connection method. For high-strength bolts, use a special wrench to tighten the nuts, so that the bolts can generate a large and well-controlled pre-tension force. According to the nuts and spacers, a small pre-working pressure of the same size also appears on the connected parts. Under the influence of pre-working pressure, a relatively large friction force will be generated along the surface of the connected parts. Obviously, as long as the load is lower than this friction force, the component will not move and the connection will not be damaged. This is the basic principle of high-strength bolt connection. The high-strength bolt connection relies on the friction force between the contact areas of the connecting parts to prevent them from moving each other. In order to ensure sufficient friction force in the contact area, it is necessary to increase the clamping force of the components and increase the friction coefficient of the contact area of ​​the components. The clamping force between components is achieved by adding pre-tensioning force to the bolts, so the bolts must be made of high-strength steel plates, which is the main reason for calling them high-strength bolt connections. In high-strength bolted connections, the friction coefficient has a great influence on the load-carrying capacity. Experiments show that the coefficient of friction is mainly affected by the form of the surface and the material of the component. In order to improve the friction coefficient of the contact area, engineering construction often chooses to repair the contact area of ​​the components within the connection range by means of sandblasting and cleaning with a steel brush.