5.2 : Support Reactions

A coplanar force system refers to a set of forces that all lie in the same plane and are subject to different reactions between the point of contact and the supports. Understanding how different types of supports affect coplanar forces is crucial for designing safe and reliable structures that can withstand external loads.

The purpose of the supports is to prevent the translational motion of the system by applying an equal and opposite force and to prevent the system's rotation by applying a couple of moments in the opposite direction. Depending on their purpose and application, there are three main types of supports: roller support, pin support, and fixed support.

Roller support allows translation in only one direction by providing a single reaction force normal to its surface. This type of support is frequently used where movement needs to be restricted, such as bridges that expand or contract due to temperature changes.

Pin support provides a reaction force in the plane perpendicular to its axis when subjected to an applied force. This permits rotation but restricts translational motion, making it useful for structures with cantilevers or uniform loading conditions along its length.

Lastly, fixed support prevents both translation and rotation by providing two reaction forces and a moment to any applied force. This type of support is often used in buildings due to its high degree of stability requirements.