It is now generally acknowledged that arc welding can be utilized in most types of steelwork fabrication more efficiently, and often more economically, than was possible with riveting system. In order that these advantages are maximized, it is necessary that the structure should be designed for welding. In other words, care must be taken at all stages of design to give due consideration to the stress-carrying capacities of the different types of welded joints, their behavior under different load conditions, and the basic features of the welding methodology to be employed to produce the joints. Integral to these variables is the design of the welds, whose type, size, and position become important to produce the most effective welded joints.
Fillet Weld
In fillet weld, the weld metal is deposited outside the profile of the joining elements. Figure 1.1 shows a few typical fillet welds.
Butt Weld
In butt weld, the edges of the members are butted against each other and joined by fusing the metal to produce a continuous joint. Thus, butt weld is made within the surface profile of the joining members. Depending on the
current used, the arc can melt the metal to a certain depth only. If the thickness of the members being joined is more than this depth, the edges of the members are required to be prepared to form a groove along the joint line, so that the continuity of the joint through the full thickness is achieved. The prepared groove is then filled by weld metal from the electrode. Figure 1.2 shows a few common types of butt welds.Properties of the parent metals, edge preparation, selection of the electrode, and welding parameters (current, speed, voltage, etc.) play a vital role in developing the strength of a butt welded joint.
Types of Welded Joints
A variety of joints can be formed by using the two types of welds, namely, fillet weld and butt weld. These joints can be made up from the four basic configurations described in the following paragraphs.
Butt Joints
Butt joints are commonly used to join lengths of plates (as in plate girders).
Tee Joints
Depending on the service requirement, tee joints can be formed either by fillet weld or by butt weld. Typical examples of these joints are at flange to web connections, stiffeners welded to the web, and flanges of plate girders. Figure 1.3 shows some examples of such fillet welded joints.
Corner Joints
Corner joints are commonly used in box girders and can be formed either by fillet weld or by butt weld, as shown in Figure 2.4.
Lap Joints
Lap joints are commonly formed by fillet welds. Bonding in lap joints are at the interfaces of the fillet welds only. These joints are widely used in structural fabrication work, such as connecting gussets to main members, as shown in Figure 1.5.
