The connection characteristics and basic requirements of fasteners selected by fasteners

Mechanical connection is divided into two categories: static connection and dynamic connection. The static connection is fixed to each other, and relative movement is not allowed. In the dynamic connection, each other can move relative to each other in a certain form. The connection in the steel structure is a static connection, and the threaded bolt or pin connection as a hinge or pin is a dynamic connection.

Mechanical connection can also be divided into two categories: detachable connection and non-detachable connection. After the detachable connection is disassembled, it can be reassembled and then used again (generally, it can be disassembled several times); when the non-detachable connection is disassembled, the connecting piece or the connected piece will be damaged, and it cannot be used unless it is repaired or replaced. Threaded fastener connections and pin connections are mostly detachable connections, and riveted connections are non-detachable connections.

(1) The force and transmission method of fasteners

From the perspective of the possibility of relative motion between two connected parts, the so-called connection is the constraint on the relative motion. For example, two connected parts may have relative movement in three mutually perpendicular directions and relative movement around three mutually perpendicular axes due to their own structural characteristics and no connecting parts. After connecting with the connecting piece, all the relative movement is restrained by the static connection, and only relative movement in a certain direction or relative movement around a certain axis is allowed to be connected. For these kinds of relative motions, there is a problem of the way of force. There are 4 ways to sum it up:

1. The axial force acting on the plane of the connecting surface to cause the two connected parts to separate;

2. One is the lateral force acting along the connecting surface of the two connected parts which tend to move relative to each other;

3. The rotating torque of the couple acting on a perpendicular to the connecting surface to cause the two connected parts to rotate relative to each other;

4. Acting on a couple of reversing moments perpendicular to the connecting surface to make the two connected parts turn relatively.

Of course, some connections may be subjected to this combination of forces or moments at the same time. At this time, the influence of each force or moment on each part of the connection can be analyzed separately, and then combined to find the total influence.

The fastener connection bears the load through different stress methods, how is the load transmitted in the connection? This is the problem of force transmission. In summary, there are two ways: one is to pass through the contact transmission force of the connecting part of the connected and connecting parts. At this time, the bolt shaft is stretched, sheared and squeezed, and its thread Subject to compression, bending, shearing and squeezing, other heads are also subject to appeal. If there are several connecting pieces or structural elements that transmit force (such as thread teeth) in the connection, there is often a problem of uneven force on each piece or element. The other is to transmit force through the friction of the contact surface of the connected piece in the connection, and the connecting piece serves to clamp the connected piece to ensure that there is sufficient positive pressure between the contact surfaces. If there are several connecting pieces in the connection, there is a problem of uneven friction at each connection.

Of course, there are also connections that transmit force in two ways at the same time. At this time, one way is often the mainstay.

The choice of the force transmission method is mainly based on the structure to be connected, the size and nature of the force on the connection, the manufacturing and assembly of the connecting part and the assembly process conditions. Generally speaking, when using the friction method, more consideration should be given to reliability.