To identify the conceptual properties of simple trusses. A truss is a structure composed of slender members that are connected at their ends. Planar trusses lie in a single plane and are often used to support roofs and bridges. In designing a truss's members and connections, three assumptions are made: All loadings are applied at the joints. The members are connected by smooth pins. All members in a truss are straight. Each member acts as a two-force member and the forces at the ends of the member must be directed along the member's axis. Because trusses consist of two-force members, each member is either in tension (being pulled apart) or in compression (being pushed together).