Why was the collapse at WTC 1 and 2 a TOTAL collapse?

Question

NIST never mentioned why there was no resistance from the below-the-impact zones. I understand that the portion above the impact zones were very heavy, but it just seems so odd that the portions above the impact zones (14 and 32 floors respectively) had enough momentum to crush both the towers ENTIRELY in 11 and 9 seconds respectively. Now if it is estimated that the free-fall speed at the height of the towers was about 9.22...then why did the towers fall in about that same time? Shouldn't the buildings have encountered more resistance? because it did have 47 core columns and 240 perimeter columns and had 93 and 77 floors of mass beneath the impact zones. Does this defy the law of momentum?

Baron,

thanks for answering, but that doesn't satisfy the asnwer im looking for. It doesn't explain to me why it fell at virtually free-fall speed....the same amount of time it would have taken if the top portions were dropped without anything beneath it.

Wraith,

Thank you too for anwering the question, but i thought that most of the jet fuel burned quickly. You have an explosion so wouldn't that mean that all or most of the jet fuel caught fire right away?

Answer 1

The steel beams are insulated to prevent excessive heat from weakening the beams during a "normal" skyscraper fire.
(Structual steel looses approximately 50% of its strength at 1100 degrees F). It is far more than just likely that this insulation was severely damaged from the impact of the plane
All of the fuel did not burn "instantly" - there wasn't sufficient oxygen for this to take place. The fuel ran down supports, elevator shafts and damaged floors where it continued to ignite in the presence of more oxygen.
Concrete litteraly "explodes" when subjected to extreme heat - think "popcorn." I have accidentally and personally experienced this on a much smaller scale with a concrete floor and a propane torch.
The only force acting on this building was gravity - and without any other forces present, this massive building is coming straight down.
When the weight of thirty or so floors above the damaged area is considered along with the instantaneous impact of the collapsing weight, the only logical conclusion one can draw is that the building had to totally collapse - anything else would have defied many physical laws.
In order to eliminate ALL resistance from the lower floors, explosives would necessarily have been placed at every key point exactly below the impact area and detonated in an exact sequence to the buildings collapse - floor by floor. Obviously, this would have taken major dismantleing of several of the walls and interior construction on each and every level exactly below the impact area. We both know full well that this didn't take place under the eyes of thousands of employees and other people visiting or doing business in the building 24/7. (And the critical timing of the explosives would have had to be impervious and independent of the fire and the extreme heat.)
The difference between static load and instantaneous impact is apparent every time you drive a nail into a piece of lumber. The static load bearing design of a skyscraper isn't going to provide much resistance to 30 floors hammering down on them - and this became apparent when the time of actual collapse was compared to freefall formulas from the same height. NIST didn't elaborate on this time to fall because it simply wasn't an issue that contridicted any of the results caused by the plane ripping damn near through the entire width of the building.

Answer 2

Each floor that collapsed added that much more to the weight, it just couldn't handle that weight. Once the fire zones collapsed, that was all she wrote.

MR Orange: Here is info from the link I gave:
Why did the building fall so quickly?
The buildings did fall quickly - almost (but not exactly) at the same speed as if there was no resistance. Shouldn't the floors below have slowed it down? The huge dynamic loads due to the very large momentum of the upper floors falling were so great that they smashed through the lower floors very quickly. The columns were not designed to carry these huge loads and they provided little resistance.

Answer 3

Believe it or not about sometime last year, there was an excellent TV program on the PBS channel. It was why the towers collapsed and what they have done to improve the structural integrity of a building now.

Anyway, it showed in engineering detail why the buildings collapsed. You see one thing too, was making a building to withstand an airplane attack was not on anyones agenda at the time. Now it is.

Answer 4

When the planes crashed into the towers they spilled burning jet fuel into the buildings support structure which allowed it flow down through the internal support beams. the intense heat from the fire damaged the hardened steel causing it to weaken and bend that kind of heat also will cause the tiny air pockets trapped in the concrete to expand cracking or "popping" the concrete further weakening the supports and making the entire tower composed of brittle concrete glass and soft steel

Answer 5

most of the answers explain what happened

also, free-fall is a myth

audio of the collapse places the falls at 14-16 seconds, nowhere near supposed "free-fall" speed

it's only at "free-fall" in kook videos when the buildings are already falling, or assumed down once they are behind other buildings

Answer 6

its easy to bring a building down with explosives just have a look around i was on a good site the over day which give you a look from the over side of the river just have a surf and you find what your looking for.