Connections are structural elements that are used for joining different members of the structural steel framework. The steel structure is the assembly of different members like beams, columns.
These various steel members are interconnected using Rivets, Bolts, and Welding. This is known as a connection. Connections can be of various types, based on different criteria.
Based on the method of fastening, the connections are of three types-Rivets, Bolts, and Welding. Based on rigidity, the connections are of three types-Rigid, Simple, and Semi-rigid.
Let us see in detail about the bolts and welded joints.
Bolts
A bolt is a metal pin with a head at one end and a shank threaded at another end to receive a nut.
A bolt connection can be used for end connections in tension and compression members. Bolts can be of many types:
Unfinished bolts or black bolts: This has a square or hexagonal bolt head and the shank area is not finished properly. So the contact between the plates and bolts is not proper. It is used for temporary connections/lightweight structures.
Finished bolts or turned bolts: The surface is finished properly. The contact would be proper.
HSFG bolts: It is made up of medium carbon steel. The class for this bolt is either 8.8 or 10.9. The force is transferred using friction, whereas in the other two cases it was bearing.
Friction bolt: The bolts are stressed up to high stress called proof stress. The bearing and shearing action of the bolt doesn’t come into play.
Bearing bolt: These bolts transfer stresses using both bearing and shearing action.
There are two types of joint, we make using bolts. These are:
Lap joints
Here, plates are overlapped with each other. The rivets are inserted in the overlapped region. The major used types of lap joints are as below:
Butt joints
In this type of riveting, the plates to be joined are kept in alignment butting/ touching, without forming an overlap. The problem in lap joints is that it produces eccentricity in loading, So, Butt joints are preferred. Butt joints are of many times.
Single cover butt joint
Double cover butt joint
Single bolted single cover butt joint
Double bolted single cover butt joint
Single bolted double cover butt joint
Double cover double bolted butt joint
The butt joints, specifically double cover butt joints are more preferred over the lap joints, because for two reasons.
Shear capacity is more in the butt joint than that of the lap joint
There is no eccentricity in the butt joint
Welded joints
When two members are connected using welds, such a connection is known as a welded connection. Welding offers an opportunity to the designer to achieve more efficient use of the materials. Reasons for choosing welded connection over bolted are
It makes the structure lighter than in the case of bolted connections.
100% efficiency can be achieved which is not possible in the case of bolted connection(70 to 80%).
Types of welds
Butt weld: It is provided when the members to be joined are lined up.
Fillet weld: When two surfaces at an angle get welded, the welding is known as fillet weld.
Slot weld or plug weld: In slot weld, when we want to join two plates, a shape is cut as a slot and the periphery of the cut is welded.
Welded joints are more rigid than bolted joints, due to the continuity of the cross-section. On the other hand, bolted joints are connected with plates or angles, and the deflection of these elements during load transfer adds flexibility. For this reason, bolted joints allow more movement with less structural stress.
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