Comparative analysis of large hexagon bolt and torsional shear bolt in steel structure

The large hexagon head high strength bolt connection pair has two washers, one on both sides of the bolt head and the nut; the torsional shear high strength bolt has only one washer, one on the nut side. The high-strength bolts with large hexagon head are divided into 8.8 and 10.9 grades, and the torsional shear type high-strength bolts are only 10.9 grades. The large hexagon head high-strength bolt adopts a torque wrench; the torsional shear type high-strength bolt adopts an electric wrench, and the box head can be broken by twisting.

In the process of construction, the final tightening torque of large hexagon is not well controlled, and the altitude is not conducive to tightening and inspection, while the good operation of torsional shear type is generally visual inspection.

The distance between high-strength bolts of torsional shear type is greater than that between high-strength bolts with large hexagon head. When the door type steel frame is connected by blue plate, the amount of torsional shear section steel is 1-5% higher than that of large hexagon head section steel, and the price of large hexagon head section steel is lower than that of torsional shear section steel. The door type steel frame of steel structure factory generally adopts the large hexagon head, and the multi-storey and high-rise buildings generally adopt the torsional shear type. In addition, there is an electric wrench with large hexagon head. For example, the distance between bolts with large hexagon head constructed by electric wrench should be increased correspondingly.

In some cases, when the electric wrench can not be used for the construction of the torsional shear bolt, the large hexagon bolt can be used. It can be detected by turning angle method, which is generally not encountered. Especially for some very large high-strength bolts, such as M33, M39, etc., if these special large bolts cannot be tested scientifically by ordinary methods, it is difficult to achieve, because the torque value of these bolts is very large, and it is difficult to achieve with torque wrench. At this time, angle method can be used, but the premise is to carry out special test in the manufacturer of high-strength bolt.

The commonly used specifications of torsional shear type high-strength bolts are M16, M20, M22 and M24. The construction quality is easy to guarantee, but the quality of domestic construction electric wrench is poor, and the unit price of imported single machine is too high. At the same time, because the unit price of torsional shear bolt is higher than that of large hexagon bolt, large hexagon high strength bolt is basically used in single-layer steel structure engineering.

During construction, the torque wrench must be checked and calibrated. If it is impossible to retest the torque coefficient of the large hexagon bolt on the project site, it is suggested that the owner and the design institute should try their best to adopt the torsional shear type high-strength bolt to ensure the construction quality. At the same time, the on-site supervision personnel need to check the electric torque wrench they use to avoid some installation teams taking extraordinary measures without special tools, resulting in hidden dangers of project quality.