Types of bolted connection performance

Types of bolted connection performance:

Bolted connections can be classified into two types, which are: support connection and friction connection.

1- Support connection performance: In cases where partial slippage between the connection plates is allowed, support connection is used. In support function, the bolt is placed in the hole of the connection plates and the nut is closed. When an external load is applied to the bolt, the parts connected by the bolt slide in the opposite direction to each other after overcoming the partial frictional resistance, resulting in a compressive force applied to the edges of the connection, which is converted into a shear force in the bolt. This connection is only for gravity loading and this type of performance should not be used in the connection in the seismic design. In this type of connection, no prestressing force is created in the bolt and to implement this connection, only tightening the bolt by the worker is sufficient.

By applying force to the connections of the above figure, the connection behavior will initially be elastic and with increasing force, the connection behavior will be plastic or plastic. The free diagram of the upper connection plate and the bolt is shown in the figure below.

As shown in the figure above, the failure of the support connection may be accompanied by the destruction of the bolt or the destruction of the plate. The types of possible failures in the support connection in which the bolts are subjected to double-sided shear are shown in the figure below.

2- Friction connection function: When the bolt is placed in the hole of the connection plates, in addition to the nut, a washer should also be used. It should be noted that the washer used in the friction connection should not be a spring washer type. According to paragraph 10-3-5-3 of the tenth topic of the 1387 edition, only this type of connection should be used in seismic design. In other words, this type of operation should be used in the design of all connections of bending frames and double frames, as well as wind connections and lateral load-bearing column joints in simple frames. In this type of connection, in addition to tightening the first bolt, a prestressing force should also be created in the bolt to the amount specified in the design. By applying the prestressing force, the bolt is pulled and by applying a load, friction is created between the connection plates, which causes no slack and full operation of the connection. It should be noted that the shape of the bolt in a friction connection is different from the shape of the bolt in a support connection. So that the friction connection bolts have a larger screw head.

According to the above figure, in a friction connection, since the friction force Nf = µTi caused by prestressing has the ability to transfer force between the connection plates, crushing force is not created under the effect of loads between the bolt body and the wall.

Requirements for the coefficient of friction of steel surfaces in friction joints:

In general, the friction is caused by two factors, one is the surface roughness and the other is the prestressing force. In the design, it is assumed that the connecting surfaces are not painted and have appropriate roughness. As a result, when the parts are installed, all connecting surfaces (including surfaces adjacent to the bolts and nuts), especially the contact surfaces of friction joints, must be completely clean and free from rust, paint, varnish, oils and other materials. Therefore, after the connection is made, the places of all the fastened screws are painted.