9/11: Twin Towers collapse9/11 Conspiracy Theories Debunked: 20 Years Later, Engineering Experts Explain How the Twin Towers Collapsed
The collapse of the World Trade Center has been subject to intense public scrutiny over the last twenty years, prompting several investigations and spawning a variety of conspiracy theories. FEMA’s report was published in 2002, and NIST’s 3-year investigation produced a report which was published in 2005. While there have been critics of both reports, their explanation for the buildings’ collapse is widely accepted. They conclude it was not caused by direct impact by the aircraft, or the use of explosives, but by fires that burned inside the buildings after impact.
The collapse of the World Trade Center has been subject to intense public scrutiny over the twenty years since the center’s twin towers were struck by aircraft hijacked by terrorists. Both collapsed within two hours of impact, prompting several investigations and spawning a variety of conspiracy theories.
Construction on the World Trade Center 1 (the North Tower) and World Trade Center 2 (the South Tower) began in the 1960s. They were constructed from steel and concrete, using a design that was groundbreaking at the time. Most high-rise buildings since have used a similar structure.
The investigatory reports into the events of September 11, 2001 were undertaken by the US Federal Emergency Management Agency (FEMA) and the National Institute of Standards and Technology.
FEMA’s report was published in 2002. This was followed by the National Institute of Standards and Technology’s three-year investigation, funded by the US Federal Government and published in 2005.
Some conspiracy theorists seized on the fact the NIST investigation was funded by the federal government — believing the government itself had caused the twin towers’ collapse, or was aware it would happen and deliberately didn’t act.
While there have been critics of both reports (and the investigations behind them weren’t flawless) — their explanation for the buildings’ collapse is widely accepted. They conclude it was not caused by direct impact by the aircraft, or the use of explosives, but by fires that burned inside the buildings after impact.
Why Did the Towers Collapse as They Did?
Some have questioned why the buildings did not “topple over” after being struck side-on by aircraft. But the answer becomes clear once you consider the details.
Aircraft are made from lightweight materials, such as aluminum. If you compare the mass of an aircraft with that of a skyscraper more than 400 meters tall and built from steel and concrete, it makes sense the building would not topple over.
The towers would have been more than 1,000 times the mass of the aircraft, and designed to resist steady wind loads more than 30 times the aircrafts’ weight.
That said, the aircraft did dislodge fireproofing material within the towers, which was coated on the steel columns and on the steel floor trusses (underneath the concrete slab). The lack of fireproofing left the steel unprotected.
