truss or frame may be defined as a structure, made up of several bars, riveted or welded together. These are made up of angle irons or channel sections and are called members of the frame or framed structure. The frames may be classified into the following two groups:
1. Perfect frame, and
2. Imperfect frame.
A perfect frame is that which is composed of members just sufficient to keep it in equilibrium, when loaded, without any change in its shape. A perfect frame should satisfy the following expression:
n = 2j-3
n = Number of members, and
j = Number of joints.
An imperfect frame is one which does not satisfy the above equation (n = 2j — 3). The imperfect frame which has number of members (n) less than 2j – 3, is known as deficient frame. If the number of members are greater than 2j – 3, Then the imperfect frame is known redundant frame.