Dapeng Town Industrial Park, Tongshan District, Xuzhou City, Jiangsu Province, China
(1) Large hexagonal head high-strength bolts
This type of bolt has a hexagonal head and is a more traditional type of high-strength bolt. Its advantages are high strength and ability to withstand large tensile and shear forces. It is widely used in steel structure connections, especially in connection parts that bear dynamic loads (such as crane beams, bridges and other structures). Large hexagonal head bolts are used in conjunction with nuts and washers, and torque is applied using a torque wrench to generate pre-tension on the bolts, thereby achieving a tight connection.
Its manufacturing process is relatively mature, the market supply is relatively sufficient, and the cost is relatively reasonable. However, during the installation process, the torque control requirements are high and it is necessary to strictly follow the specifications. Otherwise, the pre-tension may be insufficient or excessive, affecting the connection quality.
(2) Torsion shear type high-strength bolts
The head of the torsion shear type high-strength bolt is also hexagonal, but there is a plum blossom structure at the end of the bolt. The characteristic of this type of bolt is that the installation process is relatively simple. It is tightened by a special electric wrench. When the specified torque is reached, the plum head will be sheared off, thus ensuring that the pre-tension of the bolt meets the design requirements.
It has a good application effect in high-rise and large-span steel structures and can improve installation efficiency. However, the cost of torsion shear type bolts is relatively high and they are highly dependent on electric wrenches. If the electric wrench fails, it may affect the installation progress.
(1) Stress conditions
If the connection part is mainly subjected to tension, such as the tie rod connection in the steel structure, both large hexagon head high-strength bolts and torsion shear type high-strength bolts can be selected, but it is necessary to ensure that the strength grade of the bolt meets the tension requirements. For connections subjected to shear force, especially under large dynamic loads, the shear resistance of large hexagon head high-strength bolts has been verified by long-term practice and may be a more reliable choice.
(2) Installation environment and efficiency requirements
At the construction site, if there is a good power supply and a relatively clean working environment, the electric wrench installation method of torsion shear type high-strength bolts can play a high-efficiency advantage. However, if it is in the field or in places with inconvenient power supply, manual tightening of large hexagon head high-strength bolts may be more appropriate. In addition, if the installation efficiency is extremely high, such as the rapid construction of large steel structure workshops, torsion shear bolts can speed up the construction progress.
(3) Cost factors
From the perspective of material cost, large hexagon head high-strength bolts are relatively low. However, if the labor cost and time cost during the installation process are taken into account, in large-scale steel structure installation, although the material cost of torsion shear high-strength bolts is high, it may reduce the overall cost due to its efficient installation method.
(1) Torque method (applicable to large hexagon head high-strength bolts)
This is the most commonly used tightening method. Use a readable torque wrench to calculate the required torque value based on the bolt specifications, performance level and design required pre-tension. During the tightening process, strictly follow the calculated torque value, generally divided into two steps: initial tightening and final tightening. The initial tightening torque is usually 50% – 70% of the final tightening torque, so that the various parts of the connection can be initially fitted, and then the final tightening is performed to ensure that the bolt reaches the specified pre-tension.
(2) Angle method (applicable to large hexagonal high-strength bolts)
This method is to achieve the specified pre-tension by rotating the nut or bolt head at a specific angle after the initial tightening. Its advantage is that it is not affected by the accuracy of the torque wrench and the change in friction force, and can more accurately control the pre-tension of the bolt. However, it requires precise control of the initial tightening state and the angle of rotation, and requires high operating skills of the construction personnel.
(3) Torsion shear method (applicable to torsion shear type high-strength bolts)
As mentioned above, use a special electric wrench to directly tighten the bolt until the tail plum head is sheared off. This method is simple and direct, can effectively ensure the pre-tension of the bolt, and is the recommended tightening method for torsion shear type high-strength bolts. However, during use, ensure that the quality and performance of the electric wrench meet the requirements, and calibrate it regularly.
