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"WTC 7 And The Unscientific NIST Report"
posted Tue, 08-26-08
wtc 7 collapse
NIST WTC 7 Investigation Finds Building Fires Caused Collapse
The fall of the 47-story World Trade Center building 7 (WTC 7) in New York City late in the afternoon of Sept. 11, 2001, was primarily due to fires, the Commerce Department’s National Institute of Standards and Technology (NIST) announced today following an extensive, three-year scientific and technical building and fire safety investigation. This was the first known instance of fire causing the total collapse of a tall building, the agency stated as it released for public comment its WTC investigation report and 13 recommendations for improving building and fire safety.
“Our study found that the fires in WTC 7, which were uncontrolled but otherwise similar to fires experienced in other tall buildings, caused an extraordinary event,” said NIST WTC Lead Investigator Shyam Sunder. “Heating of floor beams and girders caused a critical support column to fail, initiating a fire-induced progressive collapse that brought the building down.”
“Video and photographic evidence combined with detailed computer simulations show that neither explosives nor fuel oil fires played a role in the collapse of WTC 7,” Sunder said. The NIST investigation team also determined that other elements of the building’s construction—namely trusses, girders and cantilever overhangs that were used to transfer loads from the building superstructure to the columns of the electric substation (over which WTC 7 was constructed) and foundation below—did not play a significant role in the collapse.
According to the report, a key factor leading to the eventual collapse of WTC 7 was thermal expansion of long-span floor systems at temperatures “hundreds of degrees below those typically considered in current practice for fire resistance ratings." WTC 7 used a structural system design in widespread use.
Determining the probable collapse sequence for WTC 7, NIST found that the impact of debris from the collapse of WTC 1 ignited fires on at least 10 floors of WTC 7, and the fires burned out of control on six lower floors. The heat from these uncontrolled fires caused thermal expansion of the steel beams on the lower floors of the east side of WTC 7, damaging the floor framing on multiple floors. Eventually, a girder on Floor 13 lost its connection to a critical interior column that provided support for the long floor spans on the east side of the building. The displaced girder and other local fire-induced damage caused Floor 13 to collapse, beginning a cascade of floor failures down to the fifth floor. Many of these floors had already been at least partially weakened by the fires in the vicinity of the critical column. This collapse of floors left the critical column unsupported over nine stories.
“When this critical column buckled due to lack of floor supports, it was the first domino in the chain,” Sunder explained. “What followed in rapid succession was a progression of structural failures. Failure first occurred all the way to the roof line—involving all three interior columns on the most eastern side of the building. Then, progressing from east to west across WTC 7, all of the columns in the core of the building failed. Finally, the entire façade collapsed.”
Structural Features of the Collapse
A striking feature in the collapse of WTC 7 is symmetry. The collapse progressed evenly throughout the building, and the debris piled up almost completely within the foundations of the building (see the picture below).
The symmetry of WTC 7's descent means that all of its steel supports – 25 central and 58 peripheral columns – were destroyed almost simultaneously. Any asymmetry in the damage to structures would have led to asymmetrical collapse. By contrast, a symmetrical collapse without the controlled use of explosives would violate the principle of least resistance. Local office fires (typically dying out in about 20 minutes in any given location) and structural damage here and there could not have weakened all the central and peripheral support structures in a way that would have caused all of them to fail at the same moment. The simultaneity of the destruction of support structures throughout the building can, however, be explained by controlled demolition.
Outside September 11th, highrises have toppled in earthquakes, but no completed highrise has been totally destroyed except in controlled demolition.
A controlled demolition is also suggested by the drop of the center of the skyscraper moments before the surrounding structures started to fall, as well as by the fact that the outer walls were pulled inwards. In a controlled demolition the collapse is caused by first destroying the weight-carrying core of a building, which "pulls" the exterior walls inwards ("implosion"). Although the lowest floor with fires was reportedly the sixth floor, the building seems to have undergone a traditional demolition, beginning from the bottom floor. An emergency worker who witnessed the collapse of WTC 7 was interviewed on 9/11. He described hearing what sounded like a "clap of thunder", followed by what looked like "a shockwave ripping through the building", with windows busting out, and "about a second later the bottom floor caved out and the [rest of] the building followed after that". The videos showing the collapse support his description.
Steel is very fire-resistant material. In tests conducted by Corus Construction in several countries, the fire endurance of steel-framed parking garages was examined by feeding fires with hydrocarbon fuel. Steel beams and pillars heated to a maximum of 360 degrees Celsius, and the breaking of steel was not even close. In Cardington fire endurance tests, modelled on conditions in real buildings, unprotected steel was subjected to temperatures of up to 1100 degrees Celsius (2012 F), but there was no collapse. Similarly, in the fire experiments contracted by the National Institute of Standards and Technology (NIST), testing the pancake collapse theory by modelling the fire exposure of WTC's floor assemblies, there was no collapse. Although NIST ignored the results in its final report, it acknowledged that the results "established that this type of assembly was capable of sustaining a large gravity load, without collapsing, for a substantial period of time relative to the duration of the fires in any given location on September 11th."
In the Windsor Building in Madrid, an almost 24-hour intensive fire did not collapse the building. Moreover, the fires in WTC 7 were small compared to the fires in Windsor Building and most known skyscraper fires. The latest case is the all-engulfing fire in Al Nasr Tower in 2006. Fires have never collapsed a single steel-framed highrise to the ground.
In December 2007, it was acknowledged in the advisory committee meeting of the NIST that the fires in WTC 7 were ordinary office fires and burned out in any given location in 20 minutes. In such a short time, the temperature of fire-protected steel members would have maxed out below 200 degrees Celsius (or ~400 degrees Fahrenheit). Such temperatures have no effect on construction steel.
The debris of WTC 7 was extremely hot weeks after the collapse of the building. Thermal imaging by NASA showed that the top of the debris pile had a temperature of 730 degrees Celsius five days after the collapse. Deeper, and immediately after the destruction, temperatures were probably considerably higher. Residual temperatures like this cannot be explained by office fires or by an ordinary, gravity-driven collapse. When the potential energy of a building experiencing an ordinary gravitational collapse turns into thermal energy, the result is only a few degrees' average increase in temperature.
According to several reports, molten metal was found under the debris pile of WTC buildings. To melt structural steel, temperatures exceeding 1500 degrees Celsius are required. Such temperatures are never achieved in office fires. In addition to molten metal, partly evaporated steel beams were found in the debris of WTC 7. As professor Jonathan Barnett pointed out in a New York Times interview, the fires in the building could not have produced temperatures capable of evaporating steel. However, the use of explosives like thermite can produce temperatures (even 3000 degrees Celsius) that can melt and even evaporate steel.
Craig Bartmer, a NYPD officer, states that he saw WTC 7 come down and heard a number of explosions in rapid succession. He is convinced that the skyscraper was brought down with explosives. Barry Jennings, an official of the New York City, has given a detailed statement of an explosion in WTC 7. As a result of the explosion, he and his colleague were trapped inside the building for over an hour. Several rescue personnel have also come forward saying they were told that the building would be brought down by means of explosives. Such a statement can be heard in this excerpt of Italian TV's documentary, in which one can also hear explosions from WTC 7: in one scene, a loud explosion is shown startling first responders, while a police officer says "the building is about to blow up". Interestingly, a news report on a Finnish TV channel on September 12, 2001, stated that the authorities brought Building 7 down with explosives, allegedly due to the apparent danger of collapse.
HOW DID WORLD TRADE CENTER 7 FALL?
In my opinion, the NIST conclusion that WTC 7 collapse was due to fire is unscientific hogwash. You the reader can judge for yourself. That's all I have to say!
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