The specification of high-strength bolts is a very important factor in the production, sales, and use of high-strength bolts, so it is very helpful for us to understand its requirements. In the following article, we will introduce some important contents of the specification for high-strength bolts for readers to refer to.
1, Friction type high-strength bolt
According to Chinese regulations, when installing friction type high-strength bolts, a pre tension force P is required, P=0.9 * 0.9 * fu * Ae/1.2. This means that during the installation process, it is necessary to calculate the required pre tension according to this formula and ensure the correct application of pre tension when applying bolts. This is a crucial step in ensuring the quality of bolted connections.
2, Pressure bearing high-strength bolts
The design value of the tensile bearing capacity of the pressure bearing high-strength bolts in China is also determined based on 0.8P. However, when the contact surface sliding is allowed, its stress state is the same as that of ordinary bolts, and the bearing capacity is the strength of the bolt itself. Pressure bearing high-strength bolts are the ultimate bearing capacity state in which the screw is subjected to shear failure or hole wall compression failure when the shear force exceeds the friction force. Although the shear deformation of pressure bearing high-strength bolts is greater than that of friction type, their bearing capacity is higher than that of friction type.
3, International regulatory requirements
According to DIN standards, friction type high-strength bolts cannot be used in seismic zones. Instead, they are designed based on the strength of the bolts themselves, with only material sub factors and safety factors reduced, which is higher than the Chinese standards.
4, Acceptance specifications
The acceptance code for hexagonal high-strength bolts GB50205 requires that the torque coefficient of the large hexagonal high-strength bolt connection pair needs to be retested, while the torsion shear type high-strength bolt connection pair needs to be retested for pre tension, and can only be used after passing the test. The batch size for the re examination is 8 samples per 3000 sets. For high-strength bolt connection pairs with the same strength grade and diameter but different bolt lengths, if it cannot be confirmed that they are from the same batch, they will be considered as different specifications and should be sampled and tested separately. GB/T3632-2008 Torsion shear high-strength bolts and GB131-2006 specification for large hexagonal high-strength bolts stipulate that under the same batch of conditions, when the bolt length is ≤ 100mm, the length difference is ≤ 15mm; When the bolt length is ≥ 100mm and the length difference is ≤ 20mm, it can be considered as the same length.
summary
The specification of high-strength bolts plays a very important role in the production, sales, and use of high-strength bolts. Friction type high-strength bolts need to be pre tensioned according to specifications to ensure the quality of bolt connections. The shear deformation of pressure bearing high-strength bolts is greater than that of friction type, but the bearing capacity is higher than that of friction type. International standards have higher requirements for high-strength bolts. During the acceptance process, the torque coefficient of the large hexagonal high-strength bolt connection pair needs to be retested, while the torsion shear type high-strength bolt connection pair needs to be retested for pre tension, and can only be used after passing the test.
