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9/11 Commission

Total Progressive Collapse

Progressive collapse describes a collapse in which an initiating event leads to a disproportionate collapse. This phenomenon is rare, especially in steel-framed buildings. The phenomenon of total progressive collapse is even more rare. In fact, there appears to be no example of total progressive collapse of a steel-framed building outside of the alleged examples of the Twin Towers and Building 7.

The example of progressive collapse most often cited is the collapse of a series of cantilever floor sections on the corner of a 23-story apartment building in Newham in East London, on May 16, 1968. This event was far from a total collapse. In fact, it did not cause failures of any of the support columns of this building, and is thus not remotely applicable as an example of total progressive collapse.

Global Collapse

Despite the absence of a single example of total progressive collapse of a steel-framed building before or after 9/11/01, the alleged phenomenon is the lynchpin of the official explanation for the collapse of the Twin Towers and Building 7. As if to obscure this fact, NIST's report on the Twin Towers employs a new term for the phenomenon: global collapse, which it uses multiple times without clarifying its relationship to total progressive collapse, although it also uses the term "progressive collapse" 16 times.

The procedures and practices used in the fire resistance design of structures should be enhanced by requiring an objective that uncontrolled fires result in burnout without local or global collapse.

Removal of thermal expansion from the spandrels and equivalent slabs in the tenant area to avoid local buckling that affected convergence but had little influence on global collapse initiation

This further increased the gravity loads on the core columns. Once the upper building section began to move downwards, the weakened structure in the impact and fire zone was not able to absorb the tremendous energy of the falling building section and global collapse ensued.

As with WTC 1, once the upper building section began to move downwards, the weakened structure in the impact and fire zone was not able to absorb the tremendous energy of the falling building section and global collapse ensued.

The downward movement of this structural block was more than the damaged structure could resist, and global collapse began.

The downward movement of this structural block was more than the damaged structure could resist, and the global collapse began.

Recommendation 8. NIST recommends that the fire resistance of structures should be enhanced by requiring a performance objective that uncontrolled building fires result in burnout without local or global collapse.

page last modified: 2005-10-25
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Outside of the 9/11/01 attacks, a partial collapse of the Ronan Point apartment building is the most frequently cited example of a progressive collapse.