Ordinary bolts for steel structure construction are divided into 3 kind: A, B, C. The first two are refined bolts, which are less useful. In general, ordinary bolts all refer to C-class ordinary bolts. In some temporary connections and connections that need to be removed, C-class ordinary bolts are commonly used. The frequently-used ordinary bolts of building structures are M16, M20, M24. Some mechanical industry rough bolt diameter may be relatively large, for special use.
High-strength bolts: The material of High-strength bolts and ordinary bolts is different. High-strength bolts are generally used for permanent connections. Commonly used are M16 to M30, the performance of oversized specifications is not stable, should be used carefully. The bolt connection of the main components of the building structure generally adopt high-strength bolts.
The difference between ordinary bolt and high-strength bolt
Normal bolts are reusable, high-strength bolts are not reusable.
High-strength bolts are generally made of high-strength steel (45no. steel (8.8s), 20MmTiB (10.9S), are pre-stressed bolts, the friction type requests torque wrench to apply the specified pre-stress, and the pressure type requires the screw-off of the wobbler.
Ordinary bolts are generally made of ordinary steel (Q235) and only need to be tightened.
Ordinary bolts are generally 4.4, 4.8, 5.6 and 8.8 class. High-strength bolts are generally 8.8 and 10.9 class, of which 10.9 class are mostly.
The screw holes of ordinary bolts are not necessarily larger than high-strength bolts. In fact, the ordinary bolt screw holes are relatively small. Ordinary bolt A, B class screw hole is generally only 0.3 to 0.5mm larger than bolts. C class screw holes are generally 1.0 to 1.5mm larger than bolts.
Friction-type high-strength bolts rely on friction to transmit loads, so the difference between screw and screw hole can reach 1.5 to 2.0mm. The transfer characteristic of the pressure type high-strength bolt is to ensure that under normal use, the shear force can not exceed friction force and the same as friction type high-strength bolt. When the load is increased again, the connection plate will be relatively slipped, the connection depends on screw shearing resistance and hole wall pressure-bearing to transmit force, same as ordinary bolts, so the difference between screw and screw hole is slightly smaller, 1.0 to 1.5mm.
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