Which pattern of structural collapse occurs when exterior walls collapse simultaneously, causing the roof and upper floors to collapse on top of each other?

• A. V-shaped Collapse
• B. Pancake Collapse
• C. Lean-to Collapse
• D. A-frame Collapse

Answer: (B)

Pancake collapse is a vertical failure pattern where upper floors and the roof drop down onto the lower levels, stacking on top of one another like a stack of pancakes. When exterior walls give way across a building, the supporting floors and roof lose their ability to hold, so the collapse proceeds downward in a layered fashion, producing that stacked, multi-story debris configuration.

This differs from other patterns: a V-shaped collapse spreads debris outward as lower sections fail, a lean-to collapse occurs when the structure falls in one direction forming a wedge, and an A-frame collapse creates a triangular, inward-facing shape. Recognizing the vertical, layered nature of pancake collapse helps anticipate hazards and plan safe entry.