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.