As a senior researcher in the fastener industry, today I will introduce you to high-strength bolts, which are bolts with a performance grade of 8.8 or above. High-strength bolts are divided into torsion shear bolts and large hexagonal bolts. The reason why they are different from ordinary bolts (hexagonal bolts, stud bolts, anchor bolts) is that they are made of low-carbon alloy steel or medium-carbon steel and are heat-treated. Then the following is a summary of the four main points.

1. What are the forms of bolt damage?

⑴ The bolt rod is sheared;

⑵ The hole wall is squeezed and damaged;

⑶ The plate is pulled off;

⑷ The end of the plate is sheared;

⑸ The screw is bent and damaged.

2. What are the requirements for tightening bolts?

Tightening of ordinary bolts: The tightening order of bolts should start from the middle and proceed symmetrically to both sides. The tightening construction of bolts is based on the operator's feel and the shape of the connection joint. For large joints, double tightening should be used, that is, the two-tightening method should be used to ensure that each bolt in the joint can be evenly stressed;

The initial tightening, re-tightening and final tightening of high-strength bolt connections should be carried out in the order from the part with greater joint stiffness to the direction with less constraint, and from the center of the bolt group to the surrounding areas; for connection nodes that use both high-strength bolts and welding, the construction sequence should be tightened first and then welded.

3. What are the design considerations for high-strength bolts?

The prestressed fastening of high-strength bolts is different from the fastening of ordinary bolts. Ordinary bolts are generally fastened with wrenches, while high-strength bolts require special equipment for operation. For inclined steel beams, special attention should be paid to the minimum operating space of the fastening equipment, otherwise some high-strength bolts will not be fastened.

4. What are the structural and process requirements for high-strength bolts?

① The high-strength large hexagonal head bolt connection pair consists of a bolt, a nut and two washers, and the torsion shear type high-strength bolt connection pair consists of a bolt, a nut and a washer;

② The installation environment temperature should not be lower than -10℃;

③ When installing on site, high-strength bolts should be able to be inserted freely into the bolt holes and should not be forced into them;

④ High-strength bolts that are over-tightened need to be replaced and the replaced bolts should be discarded and should not be reused;

⑤ The length of high-strength bolts should be calculated based on the standard of 2-3 exposed threads after the bolt connection pair is finally tightened.

The above are the relevant knowledge points about high-strength steel structure bolts. Have you learned them? Welcome to leave us a message for discussion. The editor will reply to you in time.