Pre-tension force of high-strength bolts used in grid steel structures

The shafts, nuts and sealing rings of high-strength bolts all need to be made of stainless steel plates with high compressive strength. The characteristic standards of high-strength bolts are divided into two types: 10.9 grade (20MnTiB steel and 30VB steel) and 8.8 grade (40B steel, 45 steel and 35 steel). 45 steel or 40B steel can only be used for high-strength bolts with a hole diameter not exceeding 24mm. At present, 20MnTiB has been gradually selected as the special steel for high-strength bolts in engineering projects. There are two types of high-strength bolts, atmospheric friction coefficient connection and pressure-bearing connection. The high-strength bolt friction connection transmits the external force by means of the friction force between the connected prefabricated components. When assembling, the anchor bolts should be tightened so that the extruder screw can cause a pre-tension force to clamp the contact area of ​​the prefabricated components, and the sliding friction mechanism between the contact surfaces can move each other to achieve the purpose of transmitting the external force. When the shear stress is the same as the sliding friction, this is the limit case of the connection's load-carrying capacity. The main difference between the high-strength bolt friction connection and the general anchor bolt connection is that it does not consider the bending resistance of the extruder screw and the pressure bearing of the hole wall to transmit force, but instead uses the friction of the contact area between thick steel plates to transmit force. The force transmission characteristic of the high-strength bolt pressure-bearing connection is that when the shear stress exceeds the sliding friction force, relative movement will occur between the prefabricated components, and the extruder screw will touch the hole wall, causing the extruder screw to be sheared and the hole wall to be stressed. The bearing capacity of the pressure-bearing connection is higher than that of the friction connection, but the deformation is relatively large. Not suitable for construction to take immediate driving force loads. The structure and arrangement of high-strength bolts are the same as those of general anchor bolts. 1. Pre-tensioning force of high-strength bolts The pre-tensioning force of high-strength bolts is achieved by tightening the nuts. Generally, the torque method, corner method or torsional shear belt is used. ①The torque method is to use a specially made wrench that can immediately indicate the torque, and increase the torque from the relationship between the measured torque and the tension of the anchor bolts to make it reach the set pre-tension. ②Corner method is to use a wrench to initially tighten the nut until the part that cannot be moved, and then finally to tighten the nut. That is, starting from the tightened position at the initial tightening, according to the final tightening angle determined by the hole diameter of the anchor bolt and the thickness of the plate stack, the nut is screwed to the preset angle of view automatically or manually, that is, the set pre-tension value is achieved. ③The torsional shear belt is made of high-strength torsional shear bolts. As shown in the figure below, the top of the anchor bolt is equipped with a plum blossom head. When tightening the nut, the pre-tension value can be adjusted by twisting off the cross section of the wound of the nut red plum blossom head.