The connection of high-strength bolts is divided into a pressure-type connection and a friction type connection. If the pressure-type connection does not bear the tensile force, the bolt can be screwed to the normal close state without applying pre-stress. The damage that can occur in the pressure-type connection is the same as that of the ordinary bolt connection, so the calculation content is the same, and the difference is the value of the shear strength and tensile strength related to the bolt material. Friction type connections are used to cause damage to normal use in the event of slippage, such as joints subjected to fatigue damage, and connections with repeated forces do not exist. In addition to the calculation of the slip, the friction type connection should be calculated according to the pressure type connection.
The calculation method specified by the specification is sometimes related to the type of bolt hole. The classification of the hole is shown in Figure 1.a-standard hole; b-expanded hole; c-short slot hole; d-long slot hole Figure 1 Bolt hole type (by diameter 20mm bolt as an example) 3 ordinary bolt connection calculation 311 ordinary bolt connection only bears tensile force 1 or shear force of a bolt tensile or shear bearing capacity The distance from the edge of the hole in the direction of the force to the edge of the adjacent hole or the distance to the edge of the connecting member; t is the thickness of the connecting piece; Fu is the minimum tensile strength of the connecting member; d is the nominal diameter of the bolt. For the connection, the total pressure resistance is the sum of the pressure values ​​of the individual bolts. Both the friction type and the pressure type connection are subjected to the calculation of the bearing strength. The enlarged holes and the short and long slots are used and the force is parallel to the direction of the slots, and the friction type connection is used. The two steel plates are bolted together, as shown in Figure 2, using M22, A325 high-strength bolts, which are standard holes, friction-type connections, and threads at the shear plane. The steel plate contact surface treatment is Class A. The design considers the deformation around the bolt holes. Find the bearing capacity Pu of the connection. Figure 2 is a simplified diagram of the calculation of the example: look up the table, A325 bolt, thread at the shear plane, shear strength F; when the diameter is 22mm, the standard hole diameter is 24mm, the ultimate strength of the pre-tensioned steel.
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