Example 3: Draw the complete free-body diagram of the structure shown.
The structure is made up of beam ABC and the angle bracket BDE. The beam is fixed at point A. The bracket is pinned at point E and is in contact with the beam through a roller at B.
We first draw the free-body diagram of the structure as a single unit by removing the supports at A and E and showing the corresponding reactions with assumed senses.
It is also possible to go one step further, and separate the two parts in contact at B. Since the roller is perpendicular to the beam, there will be a normal (vertical) force acting at B. Assuming the surface of contact is smooth, there will be no friction force. Therefore, the two free-body diagrams are shown as
Notice the action and reaction at point B as a consequence of the third law of Newton. A closer examination reveals that the bracket BDE is a three-force member.