What is high strength bolt friction type connection

1. Wrong understanding of the concept of high strength bolt connection pair
There is no correct understanding of what high strength bolt is, and even mistakenly believes that the torsional shear high strength bolt is friction type, while the large hexagon high strength bolt is pressure bearing type.  
The full name of high-strength bolt in production is high-strength bolt connection pair, which is not generally referred to as high-strength bolt. Each connecting pair includes a bolt, a nut and two washers, which are produced in the same batch and processed in the same heat treatment process. According to the installation characteristics, it is divided into large hexagon head bolt and torsion shear bolt. According to the performance grade of high strength bolt, it can be divided into 8.8 grade and 10.9 grade, and the torsion shear type is only used in grade 10.9. In the 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 ratio, that is, the ratio between the measured yield strength and the measured ultimate tensile strength. Grade 8.8 indicates that the tensile strength of the bolt rod is not less than 800MPa and the yield ratio is 0.8; grade 10.9 indicates that the tensile strength of the bolt rod is not less than 1000MPa and the yield 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, and under normal circumstances, M16 / M20 / M24 / M30 is the main choice. When assembling high strength bolt connection pair, the side of nut with round table should face the side with chamfer of washer. The chamfered side of the washer under the bolt head should face the bolt head when assembling the large hexagon head high strength bolt connection pair.

2. It is clearly stipulated in the code for acceptance of steel structures (GB 50205) that the manufacturer and the installation unit shall carry out anti sliding test and re inspection respectively (clause 6.3.1). The anti sliding coefficient must be greater than or equal to the design value. When making the test pieces on site, the test pieces and the steel structure members should be made of the same material and batch, adopt the same friction surface treatment process and have the same surface state, and adopt the same batch of high-strength bolt connection pairs with the same performance grade, and store them in the same environment for anti sliding test. If the components are finished products, in addition to the anti sliding coefficient test report in the factory, the manufacturer shall also provide three groups of test pieces for each batch to inspect whether the anti sliding coefficient meets the requirements after the components enter the site.  
In the inspection of engineering data, many construction sites only have the test report of anti sliding coefficient of the manufacturer in the factory, but lack the retest report of the anti sliding coefficient of the test pieces provided to the construction site.
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