Frames:

1. Support loads.

2. Usually stationary.

3. Fully constrained.

Not all forces are directed along the members as in a truss. In a member of truss, forces are directed along the member only. For example, in the following illustration, truss is subjected to compressive forces.

 

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L4 : Frames

A structure is called a frame if at least one of its individual members is a multiforce member. A multiforce member is defined as one with three or more forces acting on it, or one with two or more forces and one or more couples acting on it. Frames are structures which are designed to support applied loads and are usually fixed in position.