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911Research.WTC7.net site last updated:3/21/13
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Background Attack Aftermath Evidence Misinformation Analysis Memorial

Collapse Theories

Theories Purport to Explain the Unexplainable

All theories to be taken seriously must explain the collapses of the Twin Towers as the result of some chain of events triggered by the jet collisions. To this end a variety of "theories" have been advanced. They range from vague notions of forces too immense to imagine, to partial explanations with huge gaps filled in by hand-waving, but are nevertheless dignified by publication.

  • Core meltdown is more a notion than a theory. It is invoked through comparing the heat of the building fires to that of nuclear power plants, and supposes that the fires melted the structural steel. This theory can be used in conjunction with a pancake theory, but usually the idea of core meltdown is so compelling by itself that the pancake scenario isn't required. Since the core meltdown theory isn't endorsed by any official government report, it is frequently used in straw-man attacks against challenges to the official story, as in articles in Scientific American and Popular Mechanics .

  • The progressive collapse theory is the root of all the official building collapse theories. The mass of the overhanging part of the building simply crushes the part underneath, accelerating as it falls. The two major variants of the progressive collapse theory are the truss failure theory, endorsed by FEMA, and the column failure theory, endorsed by NIST.
    • The column failure theory holds that the fires weakened the columns on at least one floor sufficiently to cause the columns to buckle, and the upper section of the building to come falling down. To explain how all the columns on one level could suddenly collapse, column failure theories sometimes feature collapse initiation theories.
      • The creep buckling theory explains how the weakening of some columns due to heat could cause them to buckle, starting the spread of a kind of buckle contagion through the remaining columns.
      • The progressing column instability theory is apparently very similar to the creep buckling theory, but allows the columns to spread failure contagion without buckling. This theory is a key ingredient in NIST's Global Analysis .
      Once the columns fail in unison, it is still necessary to crush the rest of the tower from top to bottom.
      • The pile-driver theory supposes that the top of each tower acted like a giant battering ram, crushing the intact portion of the tower from top to bottom.
    • The truss failure theory blames trusses under the floors, which are more easily heated than columns, and/or their connections to the columns. The failure of the floor trusses precipitates a chain reaction of floors falling on one another, which in turn leads to total building collapse. The truss failure theory is better known as the pancake theory. To explain how a whole floor could fall, despite uneven fire stress, requires a truss failure contagion theory.
      • The zipper theory explains how all of the trusses on a floor could fall in rapid succession because of a domino-effect failure of their column connections. The zipper theory is much easier to understand if one erases, as did NOVA , the perpendicular cross-trusses and floor pans, and imagines the floor as a series of parallel trusses resting on weak angle brackets.
      Once the first floor falls on the second, it must somehow exceed the design loads of the one below, which should have been able to easily absorb the impact of the first floor falling about nine feet, especially if it didn't fall all at once. Theories that explain this generally blame some aspect of building design and/or materials.
      • The angle bracket theory helps to explain the cascade of floor collapses below the fire zone by suggesting that engineers forgot to apply standard engineering practices when designing the column connections of the floor trusses. Mis-describing the welded steel shelves that supported the truss ends as angle brackets helps us imagine this.
      Once the floor diaphragms have started to pancake down between the core and outer wall, it is still necessary to dispose of the dense steel grid constituting the outer wall, and the steel lattice of the core structure. This requires some form of sudden column failure theory. Such theories are usually only implied in tellings of the truss failure theory. Sections of the outer wall and core structure are supposed to immediately collapse from lack of lateral support once the floor diaphragms fall away. Since the perimeter wall and core structure were easily self-supporting except possibly in high winds, sudden column failure theories usually take some liberties in describing the architecture of the perimeter wall and core structures.
      • The column splice failure theory has the outer wall breaking up along column splice connections between the three-story-high by three-column-wide prefabricated sections. This theory is easier to accept if one forgets that every set of three column splice connections was surrounded on both sides by six continuous column spans, bound to the spliced columns above and below by horizontal spandrel plates four feet high.
      • The freestanding core column theory has the core columns suddenly buckling catastrophically due to lack of lateral support from the floor diaphragms. This theory depends at least on the core columns being freestanding, as the FEMA Report allows, in contrast to construction photos that show them to be cross-braced by horizontal beams and diagonal trussing.

  • The shockwave theory postulates some unspecified "shockwave" which travels ahead of the crushing mass, breaking up the building. Shockwave theories tend to be found in amateur attempts at accounting for the building collapses.


page last modified: 2007-12-16