2001-12 Why Did the World Trade Center Collapse

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<hide> <let name=data index=Date>2001-12</let> <let name=data index=Authors>\Thomas W. Eagar\Christopher Musso</let> <let name=data index=Source>The Minerals, Metals & Materials Society</let> <let name=data index=Topics>\9-11/official/papers\World Trade Center/NYC/v1/twin towers/steel\9-11/anomalies/collapse</let> <let name=data index=URL>http://www.tms.org/pubs/journals/JOM/0112/Eagar/eagar-0112.html</let> <let name=data index=Title>Why Did the World Trade Center Collapse? Science, Engineering, and Speculation</let> <let name=data index=TitlePlain>Why Did the World Trade Center Collapse</let>

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There have been numerous reports detailing the cause of the World Trade Center Tower collapse on September 11, 2001. Most have provided qualitative explanations; however, simple quantitative analyses show that some common conclusions are incorrect; for example, the steel could not melt in these flames and there was more structural damage than merely softening of the steel at elevated temperatures. Some guidelines for improvements in future structures are presented.

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The collapse of the World Trade Center (WTC) towers on September 11, 2001, was as sudden as it was dramatic; the complete destruction of such massive buildings shocked nearly everyone. Immediately afterward and even today, there is widespread speculation that the buildings were structurally deficient, that the steel columns melted, or that the fire suppression equipment failed to operate. In order to separate the fact from the fiction, we have attempted to quantify various details of the collapse.

The major events include the following:

  • The airplane impact with damage to the columns.
  • The ensuing fire with loss of steel strength and distortion (Figure 1).
  • The collapse, which generally occurred inward without significant tipping (Figure 2).

This paper is apparently considered to be part of the official story canon.

The collapse is explained thusly:

As the joists on one or two of the most heavily burned floors gave way and the outer box columns began to bow outward, the floors above them also fell. The floor below (with its 1,300 t design capacity) could not support the roughly 45,000 t of ten floors (or more) above crashing down on these angle clips. This started the domino effect that caused the buildings to collapse within ten seconds, hitting bottom with an estimated speed of 200 km per hour.

The fact that both buildings fell through the path of most resistance is also explained:

It has been suggested that it was fortunate that the WTC did not tip over onto other buildings surrounding the area. There are several points that should be made. First, the building is not solid; it is 95 percent air and, hence, can implode onto itself. Second, there is no lateral load, even the impact of a speeding aircraft, which is sufficient to move the center of gravity one hundred feet to the side such that it is not within the base footprint of the structure. Third, given the near free-fall collapse, there was insufficient time for portions to attain significant lateral velocity. To summarize all of these points, a 500,000 t structure has too much inertia to fall in any direction other than nearly straight down.

This explanation highlights the anomaly of the steel beams found horizontally embedded in neighboring buildings, however.

Eagar also seems to be unaware of the partly-melted girders and pools of molten steel found in the rubble, as he does not attempt to reconcile them with this statement:

The temperature of the fire at the WTC was not unusual, and it was most definitely not capable of melting steel.

Important Claims:

  • The cause of the collapse was not softening of the steel.
  • The cause of the collapse was mechanical changes induced by uneven heating of the steel.

As far as I know, these claims are accepted as part of the official story.

Commentary:

  • 2007-11-29 Jet Fuel Made the WTC Fires Cooler: "Thomas Eagar, a Professor of Materials Engineering and Engineering Systems at MIT and a defender of the official story" argues that the jet fuel actually reduced the heat of the fires somewhat.

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