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

where

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.