What happens when both members of a 2-member joint have no external forces?

• A. It forms a zero force member
• B. It indicates a structural failure
• C. It creates excess weight on the structure
• D. It provides unnecessary reinforcement

Answer: (A)

When both members of a two-member joint have no external forces acting on them, they can be classified as zero force members. This concept is fundamental in structural analysis and is based on certain criteria that determine when a member is unnecessary for carrying loads in a structure.

In a joint with only two members and no external load or support applied at that joint, both members cannot effectively resist any loading, making them zero force members. The primary function of these members is to maintain the structure's geometry; they do not contribute to the stability or transfer of loads. Recognizing zero force members is crucial for simplifying analysis and understanding structural behavior, as it helps engineers focus on the effective load-bearing members in the framework.

The other options do not accurately describe the situation. Structural failure would imply that the structure is no longer viable, while excess weight does not arise merely from the presence of members that are not actively contributing to load-carrying. Unnecessary reinforcement would suggest that materials are adding redundancy without purpose, but zero force members do provide geometric stability even if they carry no load.