Trusses are structures made of up slender members, connected at joints which can be approximated to pinned connections. It is typically assumed that loads are applied to the joints of the truss, not directly to the members. Because of this, the members-only carry axial forces – they do not carry bending moments. The internal force in each member is constant, and a member can be either in tension or in compression. It is important for engineers to be able to determine the axial force in the members of a truss so that they can be designed appropriately.
In this video, I cover the two main methods for doing this, which are the Method of Joints and the Method of Sections. The Method of Joints involves applying the equilibrium equations to solve the internal forces acting on every joint within the truss. The Method of Sections involves creating an imaginary cut through the members of interest and applying the equilibrium equations to the external and internal forces.