Nearly everyone was shocked to see the towers explode into dust in mid-air, including engineers. We were not given any time to ask how this happened, as the official explanation was already at hand to provide a narrative for the broadcast images: the buildings, we were told, collapsed of their own weight.
We were told that no-one had ever anticipated fuel-laden jumbo-jets crashing into the towers, and that the jet fuel burned with the heat of a nuclear power plant and melted the steal columns of the towers' cores. Faced with the fact that a jet fuel fire could only reach a fraction of the temperature required to melt the buildings' structural steel, the "truss theory" was promoted within days of the disaster. Later endorsed by FEMA, It holds that the fires weakened flimsy trusses supporting the floors, causing the floors to fall on one another in a chain-reaction.
This document examines fallacies in the official explanation:
After the disaster the site was sealed off. People were threatened with arrest for merely taking pictures of Ground Zero. Controlled Demolition Inc., one of the subcontractors involved with the "clean up" operation, helped implement a plan by which virtually all of the steel was expeditiously shipped overseas to be melted down, without ever being subjected to serious forensic analysis. FEMA's own investigators were denied access to the most important physical evidence: the buildings' structural steel.
The site of the vast crime that "changed everything", and of the largest and least understood structural failures in the history of the world, was not allowed to be analyzed for clues.
Nor can the public verify details about the buildings' design crucial to FEMA's theory, since the blueprints have not been released. The description of the towers' structure in their official report leaves over 20% of the steel known to have been used in their construction unaccounted for.
Each tower was designed to survive the impact and fire from a collision by a 707-340 carrying 23,000 gallons of fuel. The similar-sized 767-200s that hit the towers were each carrying about 10,000 gallons of fuel.
The towers' cores were their gravity load bearing components. Standard engineering practices dictated that they be built to withstand around five times anticipated loads. It was not a windy day, and the floors above the impact zones were probably holding well under half their rated loads. So an event would have to cause the simultaneous failure of at least 90% of the cores' steel columns to induce anything approaching the rapid and vertical collapses seen. The official explanation cannot account for such an event.
If WTC towers 1 and 2 and WTC 7 collapsed because of the fires it would be the first time in history that a steel-frame skyscraper totally collapsed because of fires or any cause causes other than controlled demolition and, in rare cases, severe earthquakes. 47-story WTC 7 sustained no impacts from aircraft or large falling objects, and only small fires were observed within it prior to its precisely vertical "collapse".
Since jet fuel (kerosene) boils easily and its vapors ignite easily, it burns off rapidly. FEMA admits the fuel must have been used up within "a few minutes". Thereafter the fire was fueled by the same materials as an ordinary office fire. As time went on the smoke became darker, indicating the fires were smothering for lack of oxygen. Shortly after each collision, the impact hole became and remained dark -- no light or flames were visible within. After the South Tower had been hit, at least 18 people evacuated from above the impact zone down stairwells passing through it.
There is no evidence that, even at their hottest immediately after the impacts, the fires approached the 700 degrees C required to significantly soften steel. Such temperatures would have caused regions of the building to glow red hot in broad daylight. The oxygen-starved fires likely remained below 350 degrees C, and would be harmless to the steel frame even in the absence of insulation. There is no evidence that the fires ever damaged the core structures. Note that softening of steel by high temperatures is reversible, and that steel is a good conductor of heat. If any structural steel had lost strength in the first minutes of the fires, it would have regained most of it as the fires cooled after consuming the jet fuel.
The towers fell almost perfectly vertically, while spewing debris laterally. It is impossible that the aircraft impacts and fires could result in damage so perfectly synchronized and symmetrical as to cause the simultaneous and balanced failures in the structure required for such vertical collapses.
The official explanation that the outer wall channeled the collapse to within the building's footprint doesn't fit the reality that the outer wall was shredded before the bulk of the falling mass reached it. It also fails to acknowledge that the dense core would make the building's top fall like a tree.
In a gravity-driven collapse of the type we were told happened, the floors would crash down within the outer wall, and the wall's steel columns might buckle. The core would remain standing even if the outer wall fell apart.
The explosive disintegrations we witnessed don't look anything like that. Thick clouds of dust and debris are seen billowing from the towers even in the first seconds of their destructions when their tops were falling slowly. Seismic records show the largest movement at the beginning of tower's "collapse". A gravity-driven collapse would cause peak movement at the end, when the falling rubble hit the ground.
The towers exploded into columns of dust resembling the pyroclastic flows of volcanoes. The thick clouds of pulverized concrete were ejected at regular intervals well below the 'collapse zone', meaning the pulverization was caused by forces other than gravity-driven collapse.
The steel box-beam grids of the buildings' outer walls were chopped onto small sections, and hurled tens and hundreds of feet, rather than peeling off. The massive steel box beams of the cores were also broken up into short pieces.
The collapse of floors and buckling of the outer walls proposed by the "truss theory" cannot account for the conversion of the concrete into dust in mid-air, the fine chopping of the outer walls, or the complete destruction of the buildings' resilient cores.
The towers fell at near the speed of a falling object encountering no resistance. It is generally accepted that both towers fell completely in little more than 10 seconds -- only slightly longer than would take an object in free-fall to fall the towers' height. But unless the intact portion of the building were demolished before the falling portion encountered it, it would have greatly slowed the fall, as the kinetic energy of the falling mass wound be tapped to crush each story encountered and accelerate its mass downward.
The unimpeded free-fall of the tower's tops is proof that the towers did not collapse of their own weight.
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