154 Machine Drawing
dharm
d:\N-Design\Des10-1.pm5
10 10 p
75
XX–
10
10
45
75
225
105
30 30
400
X X
Fig. 10.7 Built-up girder
However, it should be noted that the length of the joint is decided by the load to be
resisted by the joint.
10.5.1.1Lozenze or Diamond Butt Joint
This is one kind of butt joint made either with a single or double strap. As the name implies,
the rivets in this joint are arranged in a diamond shape. Figure 10.8 shows a double strap
diamond butt joint. The joint is generally used to connect tie bars in bridge structures and roof
trusses.
10.5.2 Boiler Joints
These joints are used mainly for joining metal sheets used in the construction of boilers, water
tanks and pressure vessels. Obviously, these joints must be made air-tight, as the above vessels
are required to retain fluids and withstand internal fluid pressure as well.
For manufacturing boilers, water tanks and pressure vessels, the edges of the plates to
be joined (in case of lap joints only) are first bevelled. The plates are then rolled to the required
curvature of the shell. Holding the plates together, holes are then drilled and riveting is followed.
Boiler joints are classified as: lap joints, butt joints and combination of lap and butt
joints.
10.5.2.1 Lap Joints
In a lap joint, the plates to be riveted, overlap each other. The plates to be joined are first
bevelled at the edges, to an angle of about 80° (Fig. 10.9). Depending upon the number of rows
