What type of collapse occurs when floor supports fail in a structure, causing large sections to drop while one side remains supported?

• A. V-type
• B. Lean-To
• C. Tunnel
• D. Pancake

Answer: (B)

Lean-To collapse happens when floor or wall supports on one side fail, causing large sections to drop while the opposite side still has some support. The structure tilts or leans toward the unsupported side as a hinge forms on the supported side and the rest of the building drops away. This pattern reflects a one-sided failure where weight can no longer be carried on that side, so gravity drives the building to collapse in a leaning fashion.

This differs from other patterns: a V-type collapse involves two corners failing and the structure breaking into a V shape rather than leaning from one side. Pancake collapse describes floors giving way and piling onto one another like stacked sheets, not a single-sided lean. A tunnel collapse refers to a long, arched failure pattern, not a unilateral lean.