Construction Technology of Steel Structure Connection and High Strength Bolt

3. High-strength bolt connection construction

Bolt connection is divided into ordinary bolt connection and high-strength bolt connection. The difference between the two is that high-strength bolts are made of high-strength steel after heat treatment. High-strength bolt connection is one of the main connection methods for steel structures that are currently combined with welding. , When constructing high-strength bolts, use a special wrench to tighten the bolts and apply the specified pre-tension to them. It is characterized by convenient construction, detachable and replaceable, uniform force transmission, good joint rigidity, large bearing capacity and high fatigue strength, nuts are not easy to loose, and the structure is safe and reliable.

• General requirements. The rigidity bolt process has high requirements on materials. Whether the material is qualified or not is related to the firmness of the steel connection. If the bolts are unqualified or contaminated, the steel structure is prone to loosening and falling after connection, which will affect the quality of the building. Therefore Before use, its performance should be checked, and it should be lightly loaded and unloaded during transportation; it should be stored in a dry, ventilated, rain-proof, and moisture-proof warehouse for construction site storage. Container; during installation, the friction surface of the joint should be clean and dry.
• Installation process. The bolt connection on a joint should start from the middle of the bolt group, expand to the surrounding, and tighten one by one. The initial tightening, retightening, and final tightening of torque-type high-strength bolts should be painted with corresponding colors or marks every time they are completed to prevent leakage. High-strength bolts shall pass freely into the bolt holes. The penetration direction of multiple high-strength bolts in one joint should be consistent. The chamfered side of the washer should face the bolt head and nut, and the beveled side of the nut should face the washer. After the final screwing of the strength bolt connection pair, the exposed bolt threads should be 2~3 threads, of which 10% of the bolt threads are allowed to be exposed for 1 thread or 4 threads.
• Fastening method. There are two methods for fastening high-strength bolts, namely, the fastening of large hexagon head high-strength bolts and the fastening of high-strength bolts of torsional shear type. The connection pair of high-strength bolts with large hexagon head is generally fastened by torque method and angle method: the torque method is divided into two steps: initial tightening and final tightening. Tow, use a short wrench for initial screwing, screw the nut to the component, mark it, use a long wrench for final screwing, and screw it from the marked position to the final screwing position. The torsional shear high-strength bolts used for fastening the torsional shear high-strength bolts have a torx head at the end, and a special wrench is used for fastening. Put the sleeve on the nut and the torx head, rotate in the opposite direction, and then twist off the tail to reach the torque value.

4. Steel structure connection quality acceptance

The quality of steel structure connections shall comply with the provisions of the “Code for Acceptance of Construction Quality of Steel Structure Engineering” (GB50205-2001). Its quality inspection can be divided into one or several inspection batches according to the division principle of inspection batches of corresponding steel structure fabrication projects or steel structure installation projects. The key problem in welding is the weld. Common weld defects include cracks, weld bead, burn-through, arc craters, pores, slag inclusions, undercuts, incomplete fusion, incomplete penetration, etc. Weld defects will weaken the weld. The force area and the stress concentration at the defect will damage the connection strength, impact toughness and cold bending performance. Therefore, it is necessary to do a good job in the quality inspection of weld seams. Rigid strength bolt construction should pay attention to firmness, so that the bolt connection method can achieve the expected shear and tensile effects.

1）Weld quality inspection. The quality of steel structure welds should be inspected by visual inspection, ultrasonic inspection, radiographic inspection, impregnation inspection, magnetic particle inspection, etc. according to different requirements. Carbon structural steel should be cooled to ambient temperature after the weld seam, and low-alloy structural steel should be inspected for weld flaw detection 24 hours after welding.

2）Final tightening inspection of high-strength bolt connections. The final tightening torque check should be carried out within 48 hours after the completion of the high-strength connection pair of large hexagonal head within 1 hour. Quantity to be inspected: randomly check 10% according to the number of nodes, and not less than 10; randomly check 10% of each node to be spot-checked according to the number of bolts, and not less than 2. The final inspection of torsional shear high-strength bolt connections is marked by unscrewing the torx head.

Steel structure is an indispensable part in modern buildings. The diversification of buildings requires solid and reliable technology in the connection of steel structures. Steel structure welding and strength bolt construction are the main methods of steel structure connection, with high efficiency and high performance. Good, safe and reliable, it has been widely used in construction with good results. With the continuous improvement of society’s requirements for construction technology and the rapid development of technology, the welding technology and high-strength bolt construction technology used in steel structure connections will also become more and more perfect.