Steel Structure Bolt Usage

Let's first understand what high-strength bolts for steel structures are. Generally speaking, they are made of high-strength steel (35CrMo 35 carbon steel material, etc.) that has undergone heat treatment, and can be divided into performance levels of 8.8 and 10.9. Unlike ordinary bolts, bolts must be required to be at least 8.8. When selecting, there is no need to specify the requirements for steel grade or grade. Friction type connections are commonly used in steel structural engineering.

High strength bolts in steel structures can be divided into two types based on their stress characteristics: friction type connections and pressure type connections. The connection surface of high-strength bolt pressure bearing connection only needs to be treated with rust prevention. However, high-strength bolt friction type has the advantages of tight connection, good stress resistance, fatigue resistance, and suitability for bearing dynamic loads. However, the connection surface needs to be treated with friction surface treatment, usually using sandblasting and inorganic zinc rich paint after sandblasting.

Due to different bolt structures and construction methods, high-strength bolts in steel structures can be divided into two categories: large hexagonal head high-strength bolts and torsional shear type high-strength bolts. The large hexagonal head type and ordinary hexagonal head rough bolts are the same, and the bolt head of the torsion shear type is similar to the rivet head, but the thread end of the torsion shear type is equipped with a plum blossom clamp head and a circular groove that can control the tightening torque. This difference needs to be noted.

A bolted connection pair includes three parts: bolts, nuts, and washers. The construction and arrangement requirements for high-strength bolts are the same as those for ordinary bolts. Then it must be used in accordance with the specifications. Only grade 8.8 high-strength bolts can be used for large hexagonal heads, and grade 10.9 high-strength bolts can be used for torsion shear type high-strength bolts.

The pre tension of high-strength bolts in steel structures is achieved by tightening the nuts. Usually, the torque method, angle method, or the method of twisting the bolt tail plum blossom clamp head are used to control the pre tension force.

At present, there is a special wrench that displays torque by measuring the relationship between torque and bolt tension, and then applying torque to achieve the necessary overtension value.

The angle method is divided into two steps: initial tightening and final tightening. Simply put, initial tightening usually involves workers using an ordinary wrench to make the connected components tightly fit each other, while final tightening is based on the initial tightening position as the starting point, and the final tightening angle is determined based on the bolt diameter and plate thickness. By using a powerful wrench to rotate the nut to the predetermined angle value, the bolt tension can reach the required pre tension value. In order to prevent high-strength bolts from being affected by external environment and causing changes in torque coefficient, the initial and final tightening should generally be completed within the same day.

The stress characteristics of torsional shear type high-strength bolts are the same as those of general high-strength bolts, except that the method of applying pre tension is to control the pre tension value by twisting the section at the cut of the bolt's plum blossom head.

Friction type high-strength bolt connections rely entirely on the frictional resistance between the connected components to transmit force, and the magnitude of frictional resistance, in addition to the pre tension of the bolts, is determined by the anti slip coefficient of the friction surface determined by the surface treatment of the connected component material and its contact surface.

After reading, I believe everyone has a basic understanding of where high-strength bolts should be used and how to operate and tighten them correctly.