Torsional shear bolt strength
High-strength torsional shear bolts apply pre-tension and transmit external forces by friction. The connection of ordinary torsion shear bolts transfers the shearing force by the shear resistance of the bolt and the pressure of the hole wall. The pretension force generated when tightening the nut is very small, and its effect is negligible. In addition to its high material strength, the high strength torsion shear bolts also give The torsion shear bolt exerts a large pre-tension force, which generates a squeezing force between the connecting members, so that there is a large friction force perpendicular to the direction of the screw, and the pre-tension force, anti-slip coefficient and steel type directly affect the load of the high-strength torsion shear bolt force. According to the force characteristics, it is divided into pressure type and friction type. The calculation methods of the two are different.
The minimum specifications of high-strength torsion shear bolts are M12, commonly used M16~M30, the performance of oversized torsion shear bolts is unstable, and should be used carefully in the design. The difference between high-strength torsion-shear bolt friction type and pressure-type connection: high-strength torsion-shear bolt connection is to clamp the plate of the connecting plate through a large tightening pre-tension in the torsion shear bolt rod, which is enough to produce a large friction force. In order to improve the integrity and stiffness of the connection, when subjected to shearing forces, it can be divided into two types: high-strength torsional shear bolt friction type connection and high-strength torsional shear bolt pressure type connection according to the different design and force requirements. The difference is that the limit state is different. Although it is the same type of torsion shear bolt, it is very different in terms of calculation methods, requirements, and scope of application.
In the design of shear resistance, the friction connection of high-strength torsional shear bolts is the maximum possible frictional force provided by the tightening force of the torsional shear bolts between the external shear force reaching the plate contact surface, which is to ensure that the connection is in and out of the entire use period The shear force does not exceed the maximum friction. The plate will not undergo relative slip deformation (the original gap is always maintained between the screw and the hole wall), and the connected plate is stressed as a whole in elasticity. In the design of shear resistance, the high-strength torsional shear bolt pressure-type connection allows the external shear force to exceed the maximum frictional force. At this time, relative sliding deformation occurs between the connected plates until the torsional shear bolt rod contacts the hole wall, and then the connection The torsional shear bolt shaft shearing and hole wall pressure and the friction force between the contact surfaces of the plate are combined to transmit the force. Finally, the shearing of the shaft or the pressure failure of the hole wall is regarded as the limit state of the connection shear. 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, but only whether the design considers slip.
The friction type high-strength bolts must not slide, and the bolts do not bear shear forces. Once slipped, the design is considered to be in a damaged state, which is relatively technically mature; the pressure-bearing high-strength bolts can slide, and the bolts also bear shear forces. The ultimate damage is equivalent to ordinary Bolt damage (broken bolt or steel plate crushed.
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