Which collapse pattern is the most vulnerable to secondary collapse?

• A. Dome
• B. Pile
• C. Cantilever
• D. Wedge

Answer: (C)

Secondary collapse happens when the initial failure causes remaining structure to become unstable and fail as well, often due to redistributed loads and dynamic movement of debris. The cantilever collapse pattern is most vulnerable because the overhanging portion relies on a long, exposed lever arm. When the cantilevered part yields, the load path through the supported section experiences a sharp change, creating high bending moments and transferring stresses to nearby elements. The overhang can also swing or drop, imparting additional forces to adjacent members and increasing the chance that they will fail in sequence. This combination makes progressive or secondary collapse more likely with cantilever patterns than with dome, pile, or wedge patterns, where failures tend to be more localized or load redistribution occurs in ways that are less likely to trigger widespread additional collapse.