Collapse Mechanism
Definition
The kinematic sequence of element failures that produced the observed final geometry of the collapse, reconstructed by investigators from wreckage patterns and structural analysis.
- Basis
- Wreckage pattern and structural analysis
- Output
- Sequence of element failures leading to final geometry
- Field
- Structural failure investigation
- Related process
- Progressive collapse analysis
Common questions
Why does the sequence of failures matter more than just identifying the failed element?+
The order in which elements fail distinguishes an initiating cause (a defect, overload, or impact) from elements that failed secondarily as load redistributed after the first failure. Getting the sequence wrong can point blame at a member that only failed because something else gave way first.
What physical evidence lets investigators reconstruct the sequence?+
Fracture surfaces, deformation direction, debris stratification (what landed on top of what), and connection failure modes each carry directional evidence. Investigators combine this with structural calculations to test whether a proposed sequence is physically consistent with the load path.
Related terms
- Alternate Load Path
- A route by which loads can be redistributed around a failed element without causing progressive collapse. Its presence or absence is central...
- As-Built Drawing
- A drawing that records what was actually constructed, as opposed to the approved design drawing. Discrepancies between the two are a common...
- Load Path
- The route forces travel through a structure from their point of application to the ground. When one element fails, loads redistribute onto...
- Progressive Collapse
- A failure mode in which local structural failure triggers a sequence of failures in adjacent members, resulting in collapse disproportionate to the...
- Tie-Force Method
- A prescriptive design approach requiring minimum tensile continuity across connections so that elements can hang or span around a failed support rather...