Brief introduction of torsional shear type bolt

       According to different failure criteria, the calculation of torsional shear bolt connection can be divided into two types: friction type and pressure type. These are two calculation models or two failure criteria of the same connection, rather than two types of friction and pressure of high-strength bolts.

       There are two kinds of commonly used high-strength bolts, which are divided into 10.9 and 8.8 grades according to materials. Although there is currently a third level 9.8, the application is not yet universal. Whether it is grade 10.9 or grade 8.8 high strength bolt, friction type or pressure type connection can be adopted. In this sense, the types of high-strength bolts and connectors are two concepts. Many people think that high-strength bolts can be divided into friction type and pressure type. Each class has 10.9 and 8.8 grades. Some textbooks and reference materials are not clear about this. This concept is wrong.

       When the connection is subjected to external shear V, there will be a relative sliding trend. The friction between steel plates is caused by the extrusion pressure P, and the increase of n = P will cause the friction between steel plates. V also increases n until the maximum static friction, i. e。 The OA segment of the arrival curve. If V continues to increase, the maximum static friction will be overcome and the relative slip between the plates will begin until the bar contacts the hole wall (section BC). The maximum static friction is slightly greater than the maximum dynamic friction, which can be considered equal in engineering application. Starting from point C, when the external force increases the pin action of the bolt bar, the bearing capacity of the connection continues to increase to the maximum value at point D, and the bearing capacity of the joint also has a de decline stage. After the failure. Through the above analysis, we can see that the stress and failure of high-strength bolt connections have their own characteristics, similar to the one-way tensile of steel. If the maximum static friction is taken as the damage sign, the connection is friction type, and the bearing capacity is the maximum static friction. In fact, there is no physical damage to this connection. If the failure criterion is loosened and the pin action of bolt bar is allowed, the connection is pressure bearing type. At this time, the stress of the connecting bolt is equivalent to that of the ordinary bolt, and its failure mode mainly includes the shear failure of the bolt rod, the pressure failure of the hole wall or the tension failure of the steel plate.