INSTALLATION OF METAL CONSTRUCTIONS. TECHNOLOGICAL FEATURES. Bolted connections of metal designs

Bolted joints of steel structures, depending on the constructive solution of the joint and perceived loads, are performed on bolts of coarse, normal and high accuracy and on high-strength bolts. Bolts of coarse and normal accuracy are not used in connections that work for shears.

Holes for such connections are drilled or forced. The hole diameter is 2 ... 3 mm larger than the bolt diameter, which greatly simplifies the assembly of connections. But this significantly increases the deformability of the connection, so the bolts of coarse and normal accuracy are used to fix the connections of the direct support of one element to another, in the transmission units through the supporting table, in the form of slats, as well as in flange connections.

Connections on bolts of increased accuracy are used instead of rivets in hard-to-reach places where it is practically impossible to put rivets. The diameter of the hole in the joints on such bolts may be no more than 0.3 mm larger than the diameter of the bolts. Negative tolerance for holes is not allowed. Bolts in such precise holes fit tightly and accept shear forces well.

Connections on high-strength bolts combine ease of installation, high load-carrying capacity and low deformability. They are shear-resistant and can replace rivets and bolts of increased strength in almost all cases.

The assembly of bolted joints at the installation site includes the following operations:

■ preparation of joined surfaces;

■ alignment of bolt holes;

■ screed package of connecting elements of the joint;

■ Drill holes to the design diameter and install permanent bolts.

Preparation of joined surfaces consists in cleaning them from rust, dirt, oil, dust, straightening irregularities. Cut down or cut the burrs on the edges of the parts and holes.

The combination of the holes of all connected elements reach with the help of bushing mandrels, the diameter of which is slightly smaller than the diameter of the hole. Mandrel hammered into the holes, thanks to this they are combined. The screed must provide the necessary density of the package of the elements to be joined. The package is temporary or permanent assembly bolts; after tightening the next bolt, they additionally tighten the previous one. The required density of the collected package can be ensured when installing the bolts in the following order: the first bolt is placed in the center, the subsequent ones are evenly from the middle to the edges of the field.

The installation of permanent bolts begins after adjustment of the structure. Bolts are put in the same sequence as when the package is tightened. Bolt lengths and diameters are specified in the project.

Nuts of high-strength bolts are tightened with a calibration key, which allows to control and regulate the tension force of the bolts. In order for the bolts to withstand large tightening forces, they are made from special steels and subjected to heat treatment. Bolts allow you to have a more dense and solid connection. Under the action of shear forces between the elements being joined, friction forces arise that prevent these elements from moving relative to each other.

Finally, high-strength bolts tighten on the design force after checking the geometrical dimensions of the assembled structures. The set tension, bolts is provided by one of the following methods of regulation of efforts: on the angle of rotation of the nut; on bolt axial tension; at the time of tightening the key indicator type; by the number of impact wrenches.

Regulatory requirements for the installation of steel structures are given in Section 4 of SNiP 3.03.01-87, “DESIGN AND PROTECTIVE STRUCTURES”