(Provided the whole truss is in equilibrium, the two parts that have been cut must also be in equilibrium. This results to three equilibrium equations which can be applied to either of the two parts to determine the forces of the members at the section that have been cut.
Always assume that the unknown member forces at the cut section are in tension. By doing this, the numerical solution of the equilibrium equation will yield positive scalars for members in tension an negative scalars for members in compression (Dr. G.Saravana Kumar 1)
Truss analysis using this method is simplified if members supporting no load are identified. These members maybe be in the truss for stability purposes. They are also used to provide support to the truss if the applied load is changed.
From figure 1.0, the members at C are connected together perpendicularly and there is no external force at the joint. The free body diagram at C shows that the force in each truss ember should be zero for equilibrium to be maintained.
This method deals with graphical representation of equilibrium for each joint (Asst. Prof. Dr. Cenk Ustundug “Theory of Structures). This method unifies all the forces resulting the graphical equilibrium of each and every joint into one force.
From one vector end, a line parallel to the direction of one of the two forces is drawn, while from the other end a second line parallel to the other direction is drawn. ( Asst. Prof. Dr.