What Caused the World Trade Center Buildings to Collapse?

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Discussion Overview

The discussion centers around the causes of the collapse of the World Trade Center buildings during the 9/11 attacks. Participants explore various theories and mechanisms related to structural integrity, fire safety, and the effects of the aircraft impacts. The conversation includes technical explanations, hypotheses about demolition techniques, and the role of fireproofing materials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the buildings collapsed as if they were demolished by explosives, suggesting a controlled demolition approach.
  • Others argue that the weight of the buildings and the cascading failure of floors due to melted supports from burning jet fuel led to the collapse.
  • A participant notes that the internal support structure failed from the inside out, questioning the appearance of the collapse compared to a professional demolition.
  • One viewpoint highlights the structural design of the towers, indicating that the collapse mechanism involved one floor collapsing onto another, similar to removing blocks from a stack.
  • Concerns are raised about the adequacy of fireproofing and fire response capabilities, with some attributing the collapse to insufficient coverage of fireproofing materials on structural trusses.
  • Another participant mentions that even if one part of a truss is unprotected, it can lead to the failure of the entire floor.
  • There is a suggestion that maintenance issues over time may have contributed to the collapse, despite the initial construction being sound.
  • Some participants assert that the impact of the aircraft played a significant role in the collapse, while others downplay this factor.
  • Gravity is cited as a fundamental reason for the collapse, with discussions on how structural integrity is compromised when buildings become off-center during a fall.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the causes of the collapse, with no consensus reached on the primary factors involved. The discussion remains unresolved, with differing opinions on the roles of structural design, fireproofing, and the impacts of the aircraft.

Contextual Notes

Limitations include varying interpretations of structural integrity, the adequacy of fireproofing materials, and the specific mechanics of the collapse. Some claims depend on assumptions about the building's design and the effects of fire and impact.

Julian Solos
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World Trade Center Buildings

Why did they collapse downward as if they were being demolished through the use of explosives strategically placed and detonated by demolition professionals?
 
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Professionals know to use the weight of a building itself to aid in demolition. Parts of a building falling will cause those parts beneath to collapse. The terrorist attack duplicated this process. The jet fuel melted supports in the higher floors. As soon as those supports gave way, the floors above collapsed. The impact shattered the supports below, and the collapse cascaded all of the way down.

Had the impacts of the jets been lower down, it would have been even more disastrous. Not only would more people have been trapped, the buildings might have toppled, rather than collapsed.

Njorl
 
Because the heat from the burning jet fuel melted the internal support ring causing it to fail from the inside out.

If it were done by professionals, it may have looked the same at the beginning, but towards the end of the collapse, it wouldn't have fallen outward like it did, and it wouldn't have taken a year to clean up.
 
The WTC towers were essentially composed of three structural elements:

A central tower which was built like typical skyscrapers
A load-bearing steel exterior
and
Floors that tie the two together.

The mechanism of collapse was that one section or floor would give out, and collapse onto another. Much like knocking blocks out of a stack, the result is that the tower stays mostly upright.

It also helps that the floors are essentially only tied in at the endges and at the middle, so when the 'sandwiching' occurs, the floors can break off relatively cleanly.

Enigma - one tower fell inside out, the other fell outside in.

Although the WTC towers collapsed admirably well, there are two obvious shortcomings that they had:

One is that the fire retardant and fire response capabilities were inadequate.

The other is that all of the stairwells were concetrated at the center of the building, so it was possible for the plane to knock them all out at once.
 
"One is that the fire retardant and fire response capabilities were inadequate"

the fire proofing was adequate, the towers fell for two reasons, the first is lazy workmen not covering all the trustes with it.

the 2nd is that its well known that even if 1 part of a trustes is not protected from fire, the entire floor will fall, knocking the rest.

what i find interesting is how that one looked like it inploded, half way down everything just started to get sucked into the middle as it fell.

________________________
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/[/size]

this is what one floor looks like, the thing about this fast and easy to lay floor is that it relys on itself to keep itself up. removing 1 part makes the entire floor fail.

________________________
\/\/\/\/\/\/\/\/\/\/ /\/\/\/\/\/[/size]
.......[/size]^
.......[/size]ohnos!
 
Originally posted by Gara
"One is that the fire retardant and fire response capabilities were inadequate"

the fire proofing was adequate, the towers fell for two reasons, the first is lazy workmen not covering all the trustes with it.

the 2nd is that its well known that even if 1 part of a trustes is not protected from fire, the entire floor will fall, knocking the rest.

According to the things I've seen there were two problems with the fire retardant in the WTC, one was that the foam covering the trusses was knocked off by the colision with the jet. The other was that the sheet rock which was supposed to protect the stairwells during a fire was too flimsy.

There have been no claims that the building was built out of spec.
 
yah when it was first built, it was hunky dory.

but just with anything, it comes down to maintenance. or lack of.
 
I'm sure that the impact of the gigantic jet aircraft had nothing to do with it...
 
Originally posted by Julian Solos
World Trade Center Buildings

Why did they collapse downward as if they were being demolished through the use of explosives strategically placed and detonated by demolition professionals?
Gravity.
 
  • #10
Originally posted by Adam
Gravity.
To elaborate, stability is extremely important to structural integrity of tall buildings. If they get just a little bit offcenter (falling slightly crooked), they'll break apart.

If you remember, the top of one of the buildings (the second , I think) did begin its fall a little offcenter, but a building like that just isn't strong enough to absorb the energy of its own collapse and re-direct it sideways.
 

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