Which of the following describes a zero force member in structure analysis?

• A. All members at a 3-member joint
• B. Both members of a 2-member joint with no external forces
• C. A member subjected to compression and tension
• D. A member with a load greater than its capacity

Answer: (B)

A zero force member in structural analysis is a member that carries no force under certain conditions, and these specific conditions help to identify such members effectively.

In particular, when addressing the situation of both members in a two-member joint without any external loads or reactions connected to that joint, it is established that these members must have no force acting on them. This is because if there are only two members and no external load, those members cannot resist any applied forces, leading to the conclusion that they are zero force members. This principle is essential for simplifying analysis and understanding the behavior of structures.

Recognizing zero force members helps in the design and analysis of structures, ensuring that unnecessary material is not included in places where it does not contribute to load-bearing capacity, thus optimizing material use and improving efficiency.