Graphical method
The same analysis can be performed graphically, with forces represented by lines drawn to scale in the same direction as the corresponding forces.
The method progresses through the same steps as the analytical method but with the magnitude and direction of member forces represented graphically. This description is confined to the treatment of the first joint.
At joint 1, all that is known is the direction and magnitude of the reaction and the direction of the forces in members 1-2 and 1-3. Using this information a line is drawn to scale in the direction of the reaction force, establishing points c and d on the diagram. A line is drawn to scale from d in the direction of the member 1-2, similarly another line is drawn in the direction of 1-3 from the point c. The junction of these two lines establishes the new point a.
The process is repeated until the forces in all members are found. The method is essentially self-checking since the diagram must close and since every member at 45 degrees, for instance, must have a corresponding line in the force diagram drawn parallel to the member itself.
It is possible that this procedure leads to two points on the force diagram which are coincident. The physical interpretation of this is that the force in the corresponding member is zero.
