Final answer:
The incorrect assumption for the Method of Joints is that members are in tension, bending, or compression. In reality, truss members are assumed to only be in tension or compression, as they are idealized to be pin-connected and unable to resist moments.
Step-by-step explanation:
The Method of Joints is a process used in statics to solve for the forces in the members of a truss, which is a structure made up of members, often arranged in connected triangles, that supports loads. When applying the Method of Joints, several assumptions are made for the sake of simplicity and solvability:
- The truss is stable, meaning it can withstand the applied loads without changing shape.
- Members are assumed to be weightless to simplify calculations. In reality, members have weight, but this weight is often accounted for as external forces applied at the joints.
- Members are connected by joints that allow rotation, theoretically acting as perfect pin connections. This assumes that there are no moments (rotational forces) in the truss members.
- Members are straight, which permits analysis using geometric principles.
The incorrect assumption in the list provided in the question is that members are in tension, bending, or compression. In the analysis of trusses using the Method of Joints, members are assumed to only be in tension or compression, not bending. Truss members are designed to carry load axially and bending is typically not allowed in ideal truss analysis because the joints are pin connections and cannot resist moments.