Strength of Materials

12.5 METHOD OF SECTIONS OR METHOD OF MOMENTS

When forces in a few members of a truss are to be determined then this method is the most simple one. This method is easy since we do not need the solutions from other joints. Here, we pass a section line passing through the members in which the forces are to be determined. The section line should be such that it does not cut more than three members in which the forces are unknown. The truss on one side of the section line is treated as a free body in equilibrium under the action of external forces. The unknown forces are then determined using the equilibrium equations, ΣM = 0, ΣF_x = 0 and ΣF_y = 0. When we get a negative value of force in a member then the assumed direction is not correct and it has ...