Some Specification Requirements For High-strength Bolts

The specification for high-strength bolts is a very important factor in the production, sales, and use of high-strength bolts, so understanding its requirements is very helpful for us. In the following article, we will introduce some important content of high-strength bolt specifications for readers' reference.

1, Friction type high-strength bolt
According to Chinese regulations, when installing friction type high-strength bolts, a pre tension force P needs to be applied, P=0.9*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 key step in ensuring the quality of bolted connections.
2, Pressure bearing high-strength bolt
The design value of the tensile bearing capacity of the pressure bearing high-strength bolts in our country's standards is also determined according to 0.8P, but when the contact surface slip 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 in the ultimate bearing capacity state where the screw is subjected to shear failure or hole wall compression failure when the shear force exceeds the frictional force. Although the shear deformation of pressure bearing high-strength bolts is greater than that of friction type bolts, their bearing capacity is higher than that of friction type bolts.
3, Requirements of international norms
According to DIN standards, friction type high-strength bolts cannot be used in earthquake zones, but are designed based on the strength of the bolts themselves, with only material sub factors and safety factors being reduced, which is higher than the standards in China.
4, Acceptance standards
The acceptance specification GB50205 for high-strength bolts with hexagonal joints requires a retest of torque coefficient for large hexagonal high-strength bolt connection pairs, and a retest of pre tension for torsion shear type high-strength bolt connection pairs. Only after passing the test can they be used. The batch size for the re examination is 8 samples per 3000 sets. For high-strength bolt connections of the same strength grade and diameter but with different bolt lengths, if it cannot be confirmed that they are from the same batch, they are considered different specifications and should be sampled and tested separately. GB/T3632-2008 Specification for Twisted Shear High Strength Bolts and GB131-2006 Large Hexagonal High Strength Bolts stipulates that under the same batch conditions, when the bolt length is ≤ 100mm, the length difference should be ≤ 15mm; When the bolt length is ≥ 100mm and the length difference is ≤ 20mm, it can be considered as the same length.
summary
The specification for 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 the bolt connection. The shear deformation of pressure bearing high-strength bolts is greater than that of friction type bolts, but their bearing capacity is higher than that of friction type bolts. International standards have higher requirements for high-strength bolts. During the acceptance process, the large hexagonal high-strength bolt connection pair needs to undergo a retest of torque coefficient, while the torsion shear type high-strength bolt connection pair needs to undergo a retest of pre tension, and can only be used after passing the test.