High strength torsional shear bolts apply pre tension and transmit external forces through friction. Ordinary torsional shear bolt connections transmit shear force through anchor rods and hole walls under pressure. The pre tightening force generated when tightening the nut is very small, and the effect can be ignored. In addition to its material strength, high-strength torsional shear bolts also have high strength.
In addition, a large pre tension is applied to the torsional shear bolt, which generates compressive pressure between the connecting components, resulting in a huge frictional force perpendicular to the direction of the screw. In addition, the pre tension, anti slip coefficient, and type of steel directly affect the bearing capacity of high-strength torsional shear bolts. According to the characteristics of force, it can be divided into pressure type and friction type. These two calculation methods are different.
The minimum specification for high-strength torsional shear bolts is M12, and M16M30 is commonly used. The performance of ultra large torsional shear bolts is unstable and should be used with caution during design. The difference between high-strength torsional shear bolt friction type and pressure type connection is that high-strength torsional shear bolt connection is achieved by clamping the connection plate with a large pre tension through the torsional shear bolt rod, which can generate a large frictional force to improve the integrity and stiffness of the connection. When subjected to shear force, it can be divided into high-strength shear bolt friction connection and high-strength torsional shear bolt compression connection according to different design and mechanical requirements. The essential difference between the two is the difference in ultimate state. Although they are the same type of torsional shear bolt, there are significant differences in calculation methods, requirements, and application scope.
In shear design, the high-strength torsional shear bolt friction connection is the limit state, where the plate between the contact surfaces of the torsional shear bolt fastening force reaches the maximum possible frictional force when the external shear force is applied. That is to say, ensure that the internal and external shear forces of the connection do not exceed the maximum friction force for the entire lifespan of the connection. There is no relative slip deformation (the original gap between the screw and the hole wall is always maintained), and the connecting plate is subjected to elastic force as a whole. In shear design, in high-strength torsional shear bolt bearing connections, the external shear force is allowed to exceed the maximum friction force, causing relative slip deformation between the connecting plates until the torsional shear bolt rod comes into contact with the hole wall. Since then, the connection has relied on the shear of the bolt body and the pressure of the hole wall, as well as the frictional force between the plate contact surfaces, ultimately resulting in the ultimate state of the connection shear being the failure of the rod body shear or hole wall pressure. In short, friction type high-strength torsional shear bolts and pressure bearing high-strength torsional shear bolts are actually the same type of torsional shear bolts, regardless of whether slip is considered in the design.
Friction type high-strength bolts cannot slide and do not withstand shear forces. Once they slip, the design will reach a state of failure, and the technology is relatively mature; Compression type high-strength bolts can slide and withstand shear forces, and their ultimate failure is equivalent to the failure of ordinary bolts (bolt shear or steel plate compression).
