Prerequisite expertise in fastener connection engineering

1, ordinary fastener connection

1.1. When ordinary bolts are used as permanent connecting bolts, when there is a design requirement or doubt about its quality, the minimum tensile load of the bolts should be re-inspected. The test method is referred to the "Steel Structure Construction Quality Acceptance Specification GB50205", and the results should be consistent with The current national standard "Mechanical performance bolts, screws and studs of fasteners" GB3098. The purpose is to determine whether the tensile strength of the bolts meets the current national standard requirements.

1.2. The self-tapping screws, rivets and nails used for connecting thin steel plates should be matched with the connecting steel plates. The spacing and margin should meet the design requirements.

1.3, permanent ordinary bolt fastening should be firm and reliable, and the exposed thread should not be less than 2 buckles.

1.4, self-tapping bolts, steel rivets, nails, etc. and connecting steel plates should be tightly attached, and the appearance is neatly arranged.

2, high strength bolted connection

2.1. The steel structure fabrication and installation unit shall carry out the anti-slip coefficient test and re-inspection of the high-strength bolt-connected friction surface according to the provisions of GB50205. The components processed on site shall be tested separately for the friction surface anti-slip coefficient, and the results shall be consistent with Design requirements. The 2,000 tons of monomer project is an inspection lot. The test piece and the represented components shall be made of the same material, the same batch, using the same friction surface treatment process and the same surface state, and connected with the same strength grade of high strength bolts. , stored under the same storage conditions. The surface of the test piece should be flat and free of oil. The edges of the holes and plates are free of flash and burrs.

2.2. After the final screwing of the high-strength large hex head bolt is completed, the final tightening torque should be checked within 1 hour and within 48 hours. The inspection result should meet the requirements of GB50205.

The high-strength bolt connection sub-torque test is divided into two methods: the torque test and the corner test. In principle, the test method and the construction method should be the same.

The final bolt torque value of the strength bolt connection is calculated as follows: Tc=K·Pc·d

Where Tc----final torque value (N·m);

Pc----standard value of construction pre-tension value (kN),

D----Bolt nominal diameter (mm);

K----torque coefficient (value in the re-inspection report).

2.2.1. Torque test method: Dash the screw at the opposite end of the screw end and the nut, and return the nut to about 60°. Use a torque wrench to measure the torque value when screwing back to the original position. The deviation between the torque value and the construction torque value is within 10%.

2.2.2 Corner method test method:

1) Check whether the angle between the final starting line and the ending line drawn at the nut and the relative position after the initial screwing reaches the specified value.

2) Draw a line at the opposite end of the screw end and the nut, then loosen the nut completely, and retighten the bolt according to the specified initial tightening torque and final tightening angle to observe whether it overlaps with the original drawing line. The final twist angle deviation is within 10 °.

2.3, torsion shear type high strength bolt construction moment test method:

Observe the twisted tail of the tail. If the tail plum head is screwed off, it will be regarded as the qualified quality standard; if the tail plum head is not unscrewed, it should be tested according to the above torque method or corner method. After the final setting of the torsion-shear type high-strength bolt connection, except for the structural reasons, the number of bolts that have not been screwed off the end of the plum blossom in the final screw shall not be more than 5% of the number of bolts of the joint. . For all torsion-type high-strength bolted joints that have not been twisted off by the plum blossom head, the torsion-shear type high-strength bolt connection pair which should be screwed off by the torque method or the corner head shall be finalized by the torque method or the angle method and marked with Torque check according to the specifications.

2.4 The order of screwing of the high-strength bolting joints and the initial and double-torque torques shall comply with the design requirements and the current national industry standard “Design and Construction and Acceptance Procedures for High-Strength Bolt Connections of Steel Structures” JGJ82.

Note: The purpose of initial tightening and re-tightening of high-strength bolts is to make the friction surface close to each other, and the bolts are evenly stressed. The emphasis on the installation sequence of large nodes is to prevent the uneven pre-tension loss of the bolts in the joints and affect the rigidity of the joints.

2.5 After the high-strength bolt connection is twisted, the bolt thread should be exposed to 2-3 buckles, of which 10% of the bolts are allowed to expose 1 or 4 buckles.

2.6 High-strength bolt connection friction surface should be kept dry and tidy. There should be no flash, burrs, welding spatter, welding slag, oxygen iron sheet, dirt, etc. The outer friction surface should not be painted except the design requirements.

2.7 High-strength bolts should be free to penetrate the bolt holes. High-strength bolt holes should not be gas-cut and reamed. The number of reaming should be agreed by design. The hole diameter after reaming should not exceed 1.2d (d is the bolt diameter).

Note: Forcibly passing through the bolt will damage the thread and change the torque coefficient of the high-strength bolt connection pair. Even the nut cannot be screwed, so it is emphasized that it can penetrate the bolt hole freely. The gas cutting and reaming is very irregular, which not only weakens the effective load surface of the member, reduces the pressure transmission area, but also makes the hole reaming defects, so it is stipulated that the gas cutting and reaming are not allowed.

2.8. After the total assembly of the bolt ball node is completed, the high-strength bolt and the ball joint shall be fastened. The length of the thread of the high-strength bolt screwed into the bolt ball shall not be less than 1.0d (d is the bolt diameter), and the joint shall not be There are gaps, looseness, etc. that are not tightened.

Note: For the bolt ball node grid, the stiffness (deflection) is often weaker than the design value. The main reason is that the bolts and the high-strength bolts of the steel tube are not fastened, and the gaps and looseness are not tightened. After the system is removed, the deflection is significantly increased due to the connection gap, looseness, etc., exceeding the limits specified in the specification.

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