Which structural collapse pattern is most vulnerable to secondary collapse?

• A. Cantilever
• B. A-frame
• C. Pancake
• D. V-shaped

Answer: (A)

Secondary collapse risk is highest when a structure fails in a cantilever pattern because the remaining portion is extended far from its support, creating a long, heavy overhang that is anchored only at a narrow point. That perched mass is highly unstable and, under heat, vibration, or additional loads from firefighting, can progressively give way. A disturbance can cause the unsupported end to fail and pull more debris with it, producing a second, larger collapse. Other patterns tend to distribute debris more symmetrically or settle into a contained pile, which makes a widespread secondary collapse less likely.