What are high-strength bolts? Inspection requirements before and after installation of high-strength bolts

High-strength bolts are generally used in steel structure engineering and are high-strength bolts. And unlike other bolts, high-strength bolts can be reused. High-strength bolts are single-use, generally used for permanent links, and reuse is strictly prohibited. Today I will talk to you about high-strength bolts and their inspection requirements before and after installation for your reference.

Principle of high-strength bolts

High-strength bolts use a special wrench to tighten the nut, so that the bolt generates a huge and controlled pre-tension force. Through the nut and backing plate, the bolt is The connected parts also generate the same amount of pre-stress. Under the action of pre-pressure, a large friction force will be generated along the surface of the connected parts. Obviously, as long as the axial force is less than this friction force, the components will not slip and the connection will not be damaged. This is a high-strength bolt connection. principle.

Advantages of high-strength bolts

High-strength bolt connections have the advantages of simple construction, good stress performance, removability, fatigue resistance, and no loosening under dynamic loads. They are very popular. Promising connection methods.

High-strength bolt connections rely on the friction between the contact surfaces of the connectors to prevent them from slipping. In order to ensure that the contact surfaces have sufficient friction, the clamping force of the components must be increased and the Friction coefficient of component contact surface. The clamping force between components is achieved by applying pretension to the bolts, so the bolts must be made of high-strength steel, which is why it is called a high-strength bolt connection.

In high-strength bolted connections, the friction coefficient has a great influence on the bearing capacity. Tests show that the friction coefficient is mainly affected by the form of the contact surface and the material of the component. In order to increase the friction coefficient of the contact surface, methods such as sandblasting and wire brush cleaning are often used to treat the contact surfaces of components within the connection range during construction.

Classification of high-strength bolts

There are actually two types of high-strength bolts: friction type and pressure-bearing type.

The criterion for friction-type high-strength bolts to withstand shear force is that the shear force caused by the design load does not exceed the friction force.

The design criterion for pressure-bearing high-strength bolts is that the shaft will not be sheared or the plate will not be crushed.

Pre-installation and post-installation inspection requirements for high-strength bolt connections

1. Before construction, the high-strength large hexagon head bolt connection pair should be re-inspected according to the factory batch number for torque coefficient, its average value and standard The deviation should comply with the provisions of the current national standard "Design, Construction and Acceptance Regulations for High-Strength Bolt Connections of Steel Structures"; the torsion-shear high-strength bolt connection pair should be re-inspected for prestress according to the factory batch number, and its uniform value and standard deviation should comply with the national The current standard "Regulations on Design, Construction and Acceptance of High-Strength Bolt Connections for Steel Structures".

2. For bolted ball node steel grid structures with a building structure safety level of Level 1 and a span of more than 40m, the high-strength bolts connecting them should be subjected to surface hardness tests.

3. The manufacturer and installation unit should conduct anti-slip coefficient experiments based on the steel structure manufacturing batch.

4. After the high-strength bolt connection is installed, the torque inspection of the connecting pair must be carried out. The inspection is divided into two types: torque method inspection and rotation angle method inspection. The torque test should be completed within 48 hours after 1 hour of tightening.

5. For inspection of high-strength bolts after final tightening, the torsion-shear type high-strength bolts can be visually inspected to see whether the plum blossom head at the tail of the bolt has been screwed off; high-strength large hexagon head bolts can be knocked with a "small hammer" "Strike method" is checked one by one.

Method: Use your fingers to press the corresponding side of the nut (as close as possible to the washer), and use a small hammer weighing 0.3 to 0.5kg to hit the other side of the nut. If your fingers feel a slight tremor, that is If it is qualified, a large tremor means under-tightening or missing tightening, and no trembling at all means over-tightening. Since plastic deformation may occur in bolts after over-tightening, in order to avoid delayed fracture of the bolts, over-torqued bolts should be replaced.

That’s all the relevant information about high-strength bolts. I hope this article will be helpful to you. If you still don’t understand anything, you can leave me a message below and we will answer it for you as soon as possible.