Steel structure engineering commonly involves bolted connections, which require strict inspection to ensure structural integrity and safety. The fastener joints must be tightly secured against the connecting steel plates, with a neat and orderly appearance. Before any fastening work begins, the connection must pass inspection. Bolts are classified into 11 grades: 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9, 12.9, and so on. Among these, bolts rated at 8.8 and above are considered high-strength, while those below 8.8 (excluding 8.8) are classified as ordinary bolts.
During installation, the number of temporary bolts used at each joint should be determined based on the load applied during construction. It is recommended that no fewer than one-third of all mounting holes are filled with temporary bolts, and at least two temporary bolts should be used per connection point to ensure stability.
In permanent bolt connections, it is not allowed to use more than one washer at a single end, and large nuts should never replace washers. Fasteners must be securely tightened, with at least two exposed threads visible after tightening. For bolts designed to be loose, anti-loosening measures such as double nuts or spring washers should be used. Manual methods like spot welding can also be employed for bolts with exposed threads.
For bolted connections subjected to dynamic loads or located in critical areas, spring washers should be installed as specified by the design. These washers must be placed on one side of the nut. When working with I-beams or channel sections, it's preferable to use inclined washers to ensure the nut and bolt head support surfaces remain perpendicular to the screw axis.
Proper storage and transportation of fasteners are essential. They should be kept in a dry, rainproof, and dust-free environment, organized by type and size. Handling should be gentle to avoid damage to packaging, threads, or the fasteners themselves. Any remaining fasteners should be properly stored for future use.
Regarding specifications for bolts and nuts in steel structures, the types, sizes, and performance of high-strength bolts, standard bolts, nuts, and washers must comply with current national standards and project design requirements. All components should be fully inspected, with quality certificates, Chinese markings, and inspection reports reviewed.
The torque coefficient for high-strength large hex bolts, the tightening force for torque-shear bolts, and the minimum tensile strength of ordinary bolts must be re-tested according to national standards. A sample of eight bolts per specification should be tested, with results verified through re-inspection reports.
For high-strength large hex bolts, the tightening check should cover 10% of the bolts per node, with torque sampling performed. Each bolt should be tapped with a small hammer (0.3–0.5 kg) to assess tightness. If any connection fails, an additional 10% should be checked. If issues persist, the entire node must be re-tightened and re-inspected. Torque checks should be conducted one hour after installation and completed within 24 hours.
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