Mechanical Engineering - Engineering Mechanics - Discussion

Perfect Frame.

The frame, which is composed of such members, which are just sufficient to keep the frame in equilibrium, when the frame is supporting an external load, is known as the perfect frame. Hence for a perfect frame, the number of joints and number of members are given as n = 2j -3 Imperfect Fram An Imperfect frame is one that does not satisfy the relation between the numbers of members and number of joints given by the equation n = 2j -3. This means that the number of members in an imperfect frame will be either more or less than (2j-3) It may be a deficient frame or a redundant frame. Deficient Frame If the numbers of members in a frame are less than (2j-3), then the frame is known as a deficient frame. Redundant Frame If the numbers of members in a frame are more than (2j-3), then the frame is known as a redundant frame.

Deficient is the correct answer.

Imperfect when n>2j-3 redundant and when n<2j-3 deficient.
n=2j-3 Perfect frame.

An Imperfect frame not satisfies the relation between the number of members and a number of joints given by the equation n = 2j – 3.

This means that number of members in an imperfect frame will be either more or less than (2j-3) It is known as a redundant frame.

What is redundant?

Redundant means extra sections which are not required for its function. They are useless and only increase load on frame.

A redundant frame is the one, which has got members more than required for it to become a perfect frame.

Redundant frame is one which require no force to move it moves by itself.

Redundant frame is an extra frame in the system which has a same function as another part such that the entire system will not fail if the main part fails.

Frame n = 2j-3.

So perfect frame n = 2j-3.

Imperfect frame:

n<2j-3 (deficient frame).
n>2j-3 (redundant frame).