The mold factory teaches everyone about high-strength bolts

High strength bolts are generally not called high strength bolts.

According to the installation characteristics, it can be divided into large hexagon head bolts and torsional shear anchor bolts. Among them, the torsional shear type is only used in Grade 10.9.

According to the performance level of high-strength bolts, it can be divided into 8.8 and 10.9. In Grade 8.8, there are only large hexagon high-strength bolts. In the identification method, the number before the decimal place represents the compressive strength after the heat treatment process; The number after the decimal place represents the yield ratio, that is, the ratio of the average error of yield strength to the average error of ultimate compressive strength. Grade 8.8 means that the compressive strength of the anchor bolt rod is not less than 800MPa, and the yield ratio is 0.8; Grade 10.9 means that the compressive strength of the anchor bolt rod is not less than 1000MPa and the yield ratio is 0.9.

In the overall design, the diameter of high-strength bolts is generally M16/M20/M22/M24/M27/M30, but M22/M27 is the second selected series of products. Under normal conditions, M16/M20/M24/M30 is dominant.

In terms of bending design scheme, high-strength bolts can be divided into compression type and friction type according to the design scheme. The bearing capacity of friction type lies in the anti movement index of the force transmission friction surface and the total number of friction surfaces. The friction resistance Z of sand blasting (shot) and red rust is large, but from the perspective of the operation process, it is very harmful to the construction level of the project. Many construction units have clearly proposed whether they can reduce the requirements to ensure the construction quality of the project. The bearing capacity of the compression type is the minimum of the bending resistance of the anchor bolt and the compression resistance of the bolt rod. When there is only one connection surface, the bending bearing capacity of M16 friction type is 21.6~45.5kN, while that of M16 compression type is 39.2~48.8kN, which is better than that of friction type. In installation, the pressure resistant processing technology should be simple, and the joint surface only needs to eliminate oil stains and rust. The bearing capacity of compressive strength along the axis bar is very interesting in the steel structure specification. The value of the friction type design scheme is equivalent to 0.8 times the pre tensile force. The value of the compression type design scheme is equivalent to the reasonable total area of the extruder screw multiplied by the value of the raw material compressive strength design scheme. It looks like there is a big difference. In fact, the two values are basically the same. I have not been very clear why the standard is written that way, Why use two expressions to measure the same standard value when all the raw materials are the same?

When bearing the shear stress and the tensile resistance of the rod axis at the same time, the friction type regulation is that the sum of the ratio of the shear stress borne by the anchor bolt to the shear bearing capacity plus the stress ratio of the load borne by the extruder screw to the tensile bearing capacity is less than 1.0. The compression type regulation is that the sum of the square meters of the ratio of the shear stress borne by the anchor bolt to the shear bearing capacity plus the square meters of the ratio of the load borne by the extruder screw to the tensile bearing capacity is less than 1.0, In other words, under the same load composition, the safety reserve of compression type high-strength bolts with the same diameter in the design scheme is higher than that of friction type high-strength bolts.

In full consideration of the continuous effect of the M9 earthquake, the friction surface of the connection is likely to be invalid. At this moment, the bending bearing capacity depends on the bending capacity of the anchor bolt and the compression capacity of the parts. Therefore, the seismic code requires the calculation method of the ultimate shear bearing capacity of high-strength bolts.

Although the compression type has an advantage in the design scheme, because it belongs to the shear compression destruction form, the anchor bolt hole is a porosity type anchor bolt hole similar to the general anchor bolt, and the deformation when bearing the load effect is much higher than the friction type, so the compression type key of high-strength bolt is used for the connection of non seismic grade prefabricated components, non dynamic load bearing prefabricated components, and non continuous effect prefabricated components.

All normal application limit cases of these two forms are also different:

Friction type connection refers to the relative movement of the friction surface when the load is basically composed;

The pressure resistant connection refers to the relative movement between the connectors under the load specification;