The connecting pair includes a bolt, a nut, and two washers, all of 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 bolts and torsion shear bolts.
Each connection pair includes a bolt, a nut, and two washers, all of 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 bolts and torsion shear bolts. According to the performance grade of high-strength bolts, it is divided into grade 8.8 and grade 10.9, of which the torsional 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 of the measured value of yield strength to the measured value of ultimate tensile strength. Grade 8.8 means that the tensile strength of the bolt rod is not less than 800MPa, and the yield ratio is 0.8; Grade 10.9 means 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 M16M22M20/M24/M27/M30, but M22/M27 is the second choice series, and M16/M20/M24/M30 is the main choice under normal circumstances.
When the high-strength bolted connection pair is assembled, the side of the nut with the round table should face the chamfered side of the washer. For large hexagon head high-strength bolt connections, the chamfered side of the washer under the bolt head should face the bolt head.
According to the GB50205-2001 specification, the calculation formula of the initial torque is as follows:
Torsional shear type T0=0.065Pc*d
Large hexagonal T0＝0.05Tc
When it is finally screwed, the torsion shear type high-strength bolts are screwed off with the torx head as the tightening sign. For those that cannot be screwed off with tools except for structural reasons, the torx head that does not fall off in the final screwing shall not exceed 5% of the total number of bolts at the node, and shall be marked with the torque method according to the requirements of the specification, and the final screwing shall be carried out. Torque check.
The construction torque of the large hexagonal head high-strength bolts is determined by the following formula:
Tc—construction torque (N m);
k—the average value of the torque coefficient of the high-strength bolted connection pair (the author’s note: the actual test value of the testing organization shall prevail);
Pc—standard value of construction pre-tension for high-strength bolts (kN) (author’s note: GB50205 acceptance specification clarifies that this is the standard value of construction pre-tension for high-strength bolt connections, which is about 10% higher than the design pre-tension value of bolts in GB50017 design code , mainly considering the pretension loss.)
d—diameter of high-strength bolt screw (mm);
According to the above formula, the construction torque value reference table of commonly used high-strength bolts is listed, and the approximate construction torque of each specification bolt is provided for reference. The column of "actual torque coefficient" needs to be adjusted and determined according to the re-test results of the actual selection of high-strength bolts in a specific project. .