Notice that we are dealing with a two-dimensional force system, which means we can only use three equations of equilibrium. When we look at the free-body diagram above, we see five unknown reactions. So what should we do?
If member BDE were an inseparable part of the structure, we could not solve for the reactions using the equations of equilibrium
| Frames |
Free-Body Diagram: The structure is fixed at point A and pinned at point E. In addition, member BDE is resting on beam ABC through a roller at point B. Let's draw the free-body diagram of the structure as a whole first. |