The collapse _____ is how the building failed.

• A. Mechanism
• B. Pattern
• C. Mode
• D. Failure

Answer: (A)

Understanding how a collapse progresses—the sequence of failures that disrupts the structure’s load path—is central here. The term collapse mechanism names that physical process, describing which elements fail, in what order, and how their failure reroutes loads until the structure loses stability. That specificity is why it’s the best choice: it captures the actual way the building failed, not just what it looked like afterwards or a vague notion of failure. A pattern would describe the debris arrangement or appearance after the collapse, not the underlying process that caused it. A mode is less precise in this context, and simply saying “failure” is too vague to convey how the failure happened. In practice, identifying the collapse mechanism helps responders anticipate hazards and plan appropriate shoring or stabilization to interrupt the progression.