Which collapse pattern occurs when flooring separates from exterior bearing walls but remains supported?

The correct answer, A-frame collapse, refers to a situation where the flooring separates from the exterior bearing walls but remains supported in some manner. This type of collapse commonly occurs when external forces, such as those from a heavy load or an explosive impact, cause the walls to fail or deform, while the center part of the structure, particularly the flooring, maintains some degree of support, often from internal structural elements.

In an A-frame collapse, even though the walls may be compromised, the overall integrity of the flooring is not entirely lost, preventing it from falling to the ground completely. This can create a precarious “A-frame” shape as the structure's load continues to be distributed in a tilted manner.

Understanding this collapse pattern is crucial for rescue technicians, as it informs how structural stability can still be present, allowing for potentially safe operations to be conducted in the vicinity. Recognizing the distinct features of an A-frame collapse can aid technicians in determining safe access points and egress routes during rescue operations.

The other collapse patterns, such as lateral and vertical collapses, and reinforced collapse, reflect different structural failure mechanics that do not accurately describe the specific situation mentioned in the question.