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Background Attack Aftermath Evidence Misinformation Analysis Memorial

The Column Failure Theory

Wherein All the Columns Suddenly Become as Wet Noodles

Any explanation of the total collapse of the towers would have to account for the collapse of the columns extending the height of the towers. The column failure theory maintains that fire stress to the columns, combined with structural damage from the crashes, was sufficient to level the towers.

The column failure theory was rolled out days after the attack to replace the claims of "structural engineers" on the day of the attack that the jet fuel had melted the towers' steel. It requires that all of the columns on a story reach temperatures of 800 Celsius, well below the over-1500-degree melting point of steel. At 800 C, the steel would lose about 90% of its strength and the weight of the building above would cause the columns to buckle, and the top to begin to fall, according to the theory.

Column failure theory proponents usually invoke some combination of structural damage and fire stress to explain total collapse. Structural damage is used to explain the insufficiency of fire stress and vice versa, in a kind of circular argument.


Actual Conditions

Fires have never caused column failure in steel buildings before, but could the structural damage and fuel load from the jets have created conditions for column failure never before achieved? Perhaps theoretically, but the evidence of the actual structural damage and fires in the Twin Towers precludes those conditions.

FEMA diagrammed estimated column damage for both impacts. They show about 13 percent of the North Tower's perimeter columns broken, and 10 percent of the South Tower's broken.
The fuselage of the jet that crashed into the South Tower appears to have almost entirely missed the core structure.

Structural Damage

The impacts damaged less than 15 percent of the perimeter columns in either tower. The South Tower's core columns apparently escaped significant damage.

  • People in the towers at the time of the impacts reported sways of several feet, but the deflection was not large enough to be noticeable in any of the video footage. The sways were less than the towers experienced in winter storms.
  • The North Tower impact destroyed from 31 to 36 of the 240 perimeter columns (according to FEMA) and an unknown number of core columns.
  • The South Tower impact destroyed about 23 of the 240 perimeter columns, and probably did not damage many of the core columns. The impact hole indicates that the fuselage entered on the right end of the middle third of the southwest wall, and videos show it exiting the east corner. That implies that the plane's trajectory through the building caused the fuselage to almost entirely miss the core structure. The fact there was a passable stairwell in the core after the crash also suggests there was minimal structural damage.

Thus both towers lost less than an eighth of their perimeter columns, and the South Tower lost little of its core. Each of the impact holes were confined to five floors. The North Tower's impact was so high -- just 15 lightweight stories from the top -- that no amount of structural damage to that portion of the core would threaten the whole building. The highly redundant connection of perimeter columns via the horizontal spandrell plates on every floor assured that gravity loads of the broken columns were easily transferred to other parts of the wall.

Fire Severity

The fires were not nearly hot enough to significantly soften steel in either tower. The fires in the South Tower were small compared to other serious high-rise fires, and were diminishing at the time of its collapse.

  • In both towers, the smoke darkened a few minutes after the crashes, suggesting that most of the jet fuel had burned off. Smoke from the South Tower never lightened. Dark smoke indicates oxygen-starved fires.
  • In both towers, there were no visible areas of fire extending to large portions of multiple adjacent floors. Hot fires would have to simultaneously cover several entire floors to have any chance of heating the columns to 800 C.
  • The fires remained confined to the crash zone in the South Tower, and never spread to the other side of the building. Strong fires tend to spread.
  • The exterior columns were not visibly glowing red-hot, as they would have had they been above 700 C.

page last modified: 2013-03-20