What is high-strength bolt friction type connection

What is high-strength bolt friction type connection

1. Incorrect understanding of the concept of high-strength bolt connection pairs

There is no correct understanding of what high-strength bolts are, and even a misconception is made that torsional shear high-strength bolts are friction type, while large hexagonal high-strength bolts are pressure bearing type.

High strength bolts are commonly referred to as high-strength bolt connection pairs in production, but are not simply referred to as high-strength bolts. Each connecting pair includes a bolt, a nut, and two washers, all produced in the same batch and processed in the same heat treatment process. According to installation characteristics, it is divided into large hexagonal head bolts and torsional shear type bolts. According to the performance level of high-strength bolts, they are divided into 8.8 and 10.9 levels, with torsion shear type only used in 10.9 levels. In terms of marking method, the number before the decimal point represents the tensile strength after heat treatment, and the number after the decimal point represents the yield strength ratio, which is the ratio of the measured yield strength value to the measured ultimate tensile strength value. Grade 8.8 indicates that the tensile strength of the bolt rod is not less than 800MPa, and the yield strength ratio is 0.8; Grade 10.9 indicates that the tensile strength of the bolt rod is not less than 1000MPa, and the yield strength ratio is 0.9. In structural design, the diameter of high-strength bolts is generally M16/M20/M22/M24/M27/M30, but M22/M27 is the second choice series. Normally, M16/M20/M24/M30 is the main choice. When assembling high-strength bolt connections, the side of the nut with a circular countertop should face the chamfered side of the washer. For the assembly of high-strength bolts with large hexagonal heads, the chamfered side of the washer under the bolt head should face the bolt head.

2. The Code for Acceptance of Steel Structures GB50205 specifies that the manufacturing and installation units shall conduct anti slip tests and re inspections separately (as specified in Article 6.3.1 of the Strong Clause) for the inspection of the anti slip coefficient of the friction surface of high-strength bolt connections. The anti slip coefficient must be greater than or equal to the design value. When making specimens on site, they should be made of the same material and batch as the steel structural components they represent, using the same friction surface treatment process and having the same surface condition. They should also be connected by high-strength bolts of the same performance level in the same batch and stored in the same environment for anti slip testing. If the component is a finished product leaving the factory, in addition to the anti slip coefficient test report required in the factory, the manufacturer should also provide three sets of test pieces for each batch to inspect whether the anti slip coefficient meets the requirements on site after the component enters the site.

In the inspection of engineering data, many construction sites only have anti slip coefficient test reports from the manufacturing plant in the factory, and there is a lack of retest reports on the anti slip coefficient of specimens provided to the construction site.