When high-strength bolts are tightened, a pre tension force is generated in the screw, while a pre pressure force is generated between the contact surfaces of the connected plates. After the connection is subjected to force, the frictional force generated on the contact surfaces prevents relative sliding between the plates to achieve the purpose of transmitting external force.
High strength bolts are widely used in modern steel structure installation engineering due to their high connection strength, resistance to loosening, and easy disassembly, replacing traditional riveting and welding. High strength bolt connections are divided into friction type connections and pressure type connections. The requirement for pressure bearing connections on the friction surface is only to remove oil stains and floating rust, so here we mainly introduce friction type connections. Friction type connection relies on the frictional resistance between the connected plates to transmit internal forces, with frictional resistance as the ultimate state of the connection's load-bearing capacity. According to the formula Nbv=0.9nfuP, the design value of the bearing capacity of high-strength bolt friction type connections depends on the normal pressure between the plate stacks, namely the bolt pre tension P, the anti slip coefficient u of the contact surface, and the number of force transmission friction surfaces.
In the case of a certain pre tension of high-strength bolts, the design value of their bearing capacity depends on the anti slip coefficient of the contact surface. It can be seen that the treatment of the contact surface is crucial, and the quality of the contact surface is an important factor for the safety and reliability of the connection node. In the design, the treatment method and construction precautions of the component contact surface within the friction type connection range of high-strength bolts should be specified according to the specifications. It is best to comprehensively consider the capabilities of the construction unit and adopt feasible contact surface treatment methods.
