Types of Frames in Engineering Mechanics

Frames in Engineering Mechanics:

A frame may be defined as a structure made up of several bars, riveted or welded together. These are made up of angle irons or channnel sections and are called members of the frame or framed structure.

Types of Frames:

Though there are mainly two types of frames:

  • Perfect Frame
  • Imperfect Frame

Perfect Frame:

A perfect frame is that, which is made up of members just sufficient to keep it in equilibrium, when loaded without any change in its shape. The simplest perfect frame is a triangle, which contains three members and three joints are as shown below figure. It will be interesting to know that if such a structure is loaded, its shape will not be distorted.

Thus, for three jointed frame, there should be three members to prevent any distortion. It will be further noticed that if we want to increase a joint to a triangular frame, we require two members as shown by dotted lines in figures. Thus we see that for every additional joint to a triangular frame, two members are required.

The no. of members in a perfect frame, may also be expressed by the relation:

n = (2j – 3)

where n = no. of the members and j = no. of joints.

Imperfect Frame:

An imperfected frame is that, which doesn’t satisfy the equation:

n = (2j – 3)

In other words, it is a frame in which the no. of members are more or less than (2j – 3). The imperfect frames may be further classified into the following two types:

1. Deficient Frame: A deficient frame is an imperfect frame, in which the no. of members are less than (2j – 3).

2. Redundant Frame: A redundant frame is an imperfect frame, in which the no. of members are more than (2j – 3).