Progressive Collapse
Definition
A failure mode in which local structural failure triggers a sequence of failures in adjacent members, resulting in collapse disproportionate to the initiating event; relevant to the NIST-NCSTAR WTC analysis.
- Defining feature
- Failure severity is disproportionate to the initiating event
- Mechanism
- Loss of one element causes adjacent elements to become overloaded and fail sequentially
- Engineering relevance
- A failure mode studied in structural failure investigation methodology
Common questions
What is progressive collapse?+
Progressive collapse happens when a local failure in one structural element triggers failures in nearby members, creating a domino effect. Each failed piece adds load to the next, causing the building to fail far more severely than the initial damage would suggest.
Why is progressive collapse dangerous in structural investigations?+
It makes cause-and-effect analysis difficult because the final collapse pattern doesn't match the original triggering event. A small localized failure can cascade into total building failure, so forensic engineers must trace back through the failure chain to find the true initiator.
How does one element's failure spread to others?+
When a structural member fails, the load it was carrying gets redistributed to adjacent members. If those members are not designed to handle the extra weight, they become overloaded and fail in turn, propagating the failure through the structure.
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...
- Beach Marks
- Macroscopic curved bands on a fatigue fracture surface, visible without magnification, produced by changes in crack growth rate during service (load changes,...
- Collapse Mechanism
- The kinematic sequence of element failures that produced the observed final geometry of the collapse, reconstructed by investigators from wreckage patterns and...
- Damage-Tolerant Design
- A structural-design philosophy that assumes cracks will form and specifies inspection intervals short enough to detect and repair cracks before they reach...
- Ductile Dimples
- Microscopic cup-shaped depressions visible on a ductile overload fracture surface under SEM, formed by nucleation, growth, and coalescence of microvoids at second-phase...
- Fatigue Striations
- Microscopic parallel marks on a fatigue fracture surface, formed during individual loading cycles in Stage II crack growth. Visible by SEM at...
- Fractography
- The systematic examination and interpretation of fracture surfaces to determine the mechanism, origin, and propagation direction of fracture; uses optical and scanning...
- Load Path
- The route forces travel through a structure from their point of application to the ground. When one element fails, loads redistribute onto...
- MCAS
- Maneuvering Characteristics Augmentation System; the Boeing 737 MAX software feature that repeatedly commanded nose-down stabiliser trim based on a single AoA sensor...
- River Patterns
- Fan-shaped or river-delta-like markings on brittle-cleavage fracture surfaces that indicate crack propagation direction; rivers diverge from the origin and converge toward the...
- S-N Curve
- A plot of cyclic stress amplitude (S) against the number of cycles to failure (N), used to characterise a material's fatigue life;...
Explained in these topics
- Forensic Engineering: Failure Analysis and FractographyA failure mode in which local structural failure triggers a sequence of failures in adjacent members, resulting in collapse disproportionate to the initiating...
- Structural Failure Investigation MethodologyDisproportionate spread of failure beyond a local triggering event, where the loss of one element causes adjacent elements to become overloaded and fail in tur...