Posted on 09/11/2023 12:41:34 PM PDT by nickcarraway
Countless conspiracy theories have circulated in the wake of 9/11, the day when terrorists hijacked planes and attacked the World Trade Center in New York twenty two years ago.
By David Oswald, RMIT University; Erica Kuligowski, RMIT University, and Kate Nguyen, RMIT University
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.
Grecian Delight supports Greece 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 on 9/11? 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 of lightweight materials, such as aluminium. If you compare the mass of an aircraft with that of a skyscraper more than four hundred meters tall and built from steel and concrete, it makes sense the building would not topple over.
The towers would have been more than one thousand times the mass of the aircraft and designed to resist steady wind loads more than thirty 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.
As such, the impact also structurally damaged the supporting steel columns. When a few columns become damaged, the load they carry is transferred to other columns. This is why both towers withstood the initial impacts and didn’t collapse immediately.
Progressive collapse vs 9/11 conspiracy theories This fact also spawned one of the most common conspiracy theories surrounding 9/11: that a bomb or explosives must have been detonated somewhere within the buildings.
These theories have developed from video footage showing the towers rapidly collapsing downwards some time after impact, similar to a controlled demolition. But it is possible for them to have collapsed this way without explosives.
It was fire that caused this, and this fire is believed to have stemmed from the burning of remaining aircraft fuel.
According to the FEMA report, fire within the buildings caused thermal expansion of the floors in a horizontal and outwards direction, pushing against the rigid steel columns, which then deflected to an extent but resisted further movement.
9/11 conspiracy theories This figure shows the expansion of floor slabs and framing which likely happened as a result of the fires. Credit: FEMA With the columns resisting movement, there was nowhere else for the concrete floors to expand. This led to an increased buildup of stress in the sagging floors until the floor framing and connections gave in.
The floors’ failure pulled the columns back inwards, eventually leading to their buckling and the floors collapsing. The collapsing floors then fell on more floors below, leading to a progressive collapse.
9/11 conspiracy theories The buckling of columns initiated by floor failure. Credit: FEMA This explanation, documented in the official reports, is widely accepted by experts as the cause of the Twin Towers’ collapse. It is understood the South Tower collapsed sooner because it suffered more damage from the initial aircraft impact, which also dislodged more fireproofing material.
The debris from the collapse of the North Tower set at least ten floors alight in the nearby World Trade Center 7, or “Building 7,” which also collapsed about seven hours later.
While there are different theories regarding how the progressive collapse of Building 7 was initiated, there is consensus among investigators that fire was the primary cause of failure.
Both official reports made a range of fire safety recommendations for other high-rise buildings, including the improvement of evacuation and emergency response. In 2007, the National Institute of Standards and Technology also published a best practice guide recommending risk-reducing solutions for progressive collapse.
What does this mean for high-rise buildings? Before 9/11, progressive collapse was not well understood by engineers. The disaster highlighted the importance of having a “global view” of fire safety for a building, as opposed to focusing on individual elements.
There have since been changes to building codes and standards on improving the structural performance of buildings on fire, as well as opportunities to escape (such as added stairwell requirements).
At the same time, the collapse of the Twin Towers demonstrated the very real dangers of fire in high-rise buildings. In the decades since the World Trade Center was designed, buildings have become taller and more complex, as societies demand sustainable and cost-effective housing in large cities.
Some eighty-six of the current one hundred tallest buildings in the world were built since 9/11. This has coincided with a significant increase in building façade fires globally, which have gone up sevenfold over the past three decades.
This increase can be partly attributed to the wide use of flammable cladding. It is marketed as an innovative, cost-effective, and sustainable material; yet, it has shown significant shortcomings in terms of fire safety, as witnessed in the 2017 Grenfell Disaster.
The Grenfell fire (and similar cladding fires) are proof fire safety in tall buildings is still a problem, and as structures get taller and more complex with new and innovative designs and materials, questions around fire safety will only become more difficult to answer.
The events of 9/11 may have been challenging to foresee, but the fires that led to the towers’ collapse could have been better prepared for.The Conversation
David Oswald, Senior Lecturer in Construction, RMIT University; Erica Kuligowski, Vice-Chancellor’s Senior Research Fellow, RMIT University, and Kate Nguyen, Senior Lecturer, ARC DECRA Fellow and Victoria Fellow, RMIT University
Betty Ong, I think.
Where id the towers go? By Judy Wood B.S., M.S., Ph. D.
It is a very detailed heavily illustrated book in hardcover, unfortunately out of reach for most of the general public due to the price which currently is around $ 51.00 at Amazon. It leads us to fires in CA and Maui. Read the book. Visit her website and compare photos to Maui. Brush fire or something else? Same white dust that should be black. Boats with fiberglass hulls untouched while everything else is gone. People burning in water. Cars with melted hoods and windshields but plastic dash still in tact parked next to a palm tree with fronds still waving. Any good Catholics who burns palm fronds knows...they go up like match sticks.. Aluminum wheels melted and flowing across roads next to the ocean. If you can’t see what is wrong, you can certainly feel it. If 911 was about starting a war in the Middle East, Maui is Pearl Harbor for humanity.
Georgia Girl 2 wrote: “The conspiracy theory is that a bunch of rag heads flew airliners into the twin towers and made them collapse. I can’t find anybody I personally know who still believes it.”
What’s the latest on those thousands of indictments that were going to be tried in Gitmo in July?
Can someone explain Mohamed Attah’s passport fluttering to the ground landing atop the rubble unburned?
9/11 Commission has about the same believability as the JFK assassination commission.
John Brennan over-road State Department denial of visas for the nineteen from SA.
THIS is enough to make any human who’s brain can fog a mirror to scratch their own head.
...but there’s SO much more...
But slightly less believability as the TWA Flight 800 commission.
If 9/11 was an inside job, what happened to the crews and passengers on the planes involved? Why was Barbara Olson, who posted here on FR, never seen again after boarding Flight 77, which struck the Pentagon?
That good enough for you as another phone call??
There were in fact a number of other people who called love ones after the hijackings and before the crashes.
So what caused the destruction of the buildings?
Depends on who all you think were “terrorists”.
The FBI, CIA, and the DOD claim you are a terrorist.
I think they are.
Apparently, here on Free Republic, we are supposed to believe some sort of untold stories or theories as to what really happened that day.
Apparently, people on Free Republic have unique insights the rest of us just aren’t seeing. We are so blinded by seeing jet airplanes crash into buildings that we just aren’t seeing the big picture. We are supposed to believe something other than terrorist attacks happened.
I AGREE WITH YOU.
Klaus Schwab was in New York on 9/11 watching while having breakfast. Was he the one that orchestrated the whole thing?
Heat. And trusses. Heat is the enemy of steel.
Ironically it’s also what creates it.
Also, a meme:
Number 1 theory is thermite.
Why bring Klaus into this? Is GWB/Rummy not enough for you?
Re: 32 - It’s called ignorance, low intellect, or malicious intent.
For my money, I think a lot of it is low intellect. Some conspiracy theorists could not make it through the NIST report or any of the other dozens reports by engineering school, so they just started making crap up, or jackassin’.
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