Types of Supports and Constraints:

A structural member (namely, a beam, a truss, etc.) required to be firmed up by supports so as to function correctly. These supports impose some constraints against movements, which require be taken into account.

Concept of Constraints

A body is not always free to move in all of the directions. The limitation to the free motion of a body in any of the direction is called as constraint. For instance, a ball resting on a frictionless horizontal plane is free to move in horizontal direction but it may not move vertically downwards. Therefore, the horizontal plane restricts or constraints the motion of the ball vertically downwards.     

            In the above condition, the ball presses the plane downwards along with a force equivalent to its own weight and the plane is turn reacts on the ball or exerts an upward force equivalent to its own weight. Such a condition is expected according to Newton's third law.