Tightening methods for steel structure bolts

Steel structural bolts and their tightening methods

1、 Torque method

In order to reduce the pre tightening force difference of steel structure bolts that are tightened first and then tightened, ordinary wrenches are generally used for initial tightening (the torque value is not less than 50% of the final tightening torque value) in the process of bolt connection and tightening in steel Structural engineering, so that the steel plates overlap and are disturbed, and then a constant torque wrench that can display the torque value is used for final tightening. The final tightening torque value should be determined based on the relationship between the pre tightening torque and the pre tightening force (increase by 5% -10% after tightening to compensate for the relaxation effect), and the deviation during tightening should not exceed ± 10%.

2、 Angle method

In this method, the specified preload is obtained by controlling the bolt strain (i.e. controlling the angle of the nut). The angle starts from the marking line of the initial tightening action, and then use a long wrench (or an electric or Impact wrench) to finally tighten 1/3-2/3 turns (120 ° -240 °). The final tightening angle is related to the layer thickness and bolt diameter, and can be determined in advance.

3、 Unscrew the end of the bolt

This method is applicable to torsion shear steel structural bolts. Tighten the bolts first, and then cover the nut and bolt end with two special electric wrench sockets. During the operation, the large sleeve rotates in the forward direction to apply tightening torque, while the small sleeve rotates in the reverse direction to apply tightening torque. After tightening the bolts, unscrew the plum blossom head along the end notch.