Can anyone describe the collapse of the WTC towers using only structural knowledge of how they were built?
Answer:
gravity and weight
Firstly you have to time how long an object takes to reach the ground when dropped from the same height. Then time how long the towers took to get to street level. Ive timed it and the WTC towers took between 10 and 14 seconds to drop. (Its hard to be sure for all the dust) WTC7 took 6.5 seconds to drop. Ask yourself is it possible that all 3 buildings could break all of their welds, and joints simultaneously simply because of a few fires on the 80th or 90th storeys?
The only other way that could have happened is with pre planted steel cutting charges which were computer controlled or set off with radio frequency transmissions. There would be no need for miles of det cord and even if there was, it would be well out of sight beneath the floors, cielings and walls.
When the WTC towers were built, they were of unique design. Most skyscrapers were built using a box-like structure of steel framing. They would be riveted or bolted together, then the concrete floors would be poured, and the exterior could be something in the order of brick, or stone, etc.
The WTC was designed for optimal office space. So rather than a box-like steel interior, the outter walls were itself the main supports for the building. They were tied together for strength by steel supports, and those supports were sprayed with a fire-retardant material.
When the aircraft struck the towers, the impact destroyed the fire retardant material from these supports, as well as dumping anywhere from 16,000-20,000 gallons of jet fuel into the buildings. The heat was over 2000 degrees. When the supports overheated, they began to bend. Once they were critically weakened, they could no longer help support the upper floors on top of them. The weight was too much. So they literally collapsed. Millions of tons of steel and concrete crashed down, one floor on top of another.
One more thing.. the center of the buildings consisted of elevators, but not one continuous elevator from bottom floor to top. This also applied to the staircases. You would literally have to transfer from one elevator to another, depending on the floor, and this would be the case also in the stairwells. That is why it took so long to get the people out. Also, around the impact points, the debris kept many from getting into either an elevator, or a stairwell. So they were trapped in many cases.
The buildings failed around the point of impact. The entire building above the failure point then fell on the floors below. Due to the sheer mass of the upper part of the building, even a little velocity would have an enormous amount of momentum and energy. The lower floors collapsed with little or no resistance. As each floor collapsed, one at a time, the energy increased, since both mass (due to the addition of one more floor) and velocity (due to gravity acceleration) of the falling sections also increased.
The total time of collapse can be estimated by throwing a ball off the top of the building. The WTC was 1776 feet high and gravity accelerates at 32 ft/sec/sec.
Using position formula
distance = 1/2.acceleration.time^2 + velocity.time + starting distance
In this case velocity is 0 since the building started at rest, and starting distance is 0, since the roof of the building is our origin in this example
1776 = 1/2 x 32 x t^2 = 16t^2
t^2 = 111
t = 10.5 seconds, which is about how long it took
If the building had collapsed starting near the top (say two floors below the top), then the collapse would've either been incomplete or MUCH slower. The key to the WTC collapse was the upper half of the building was a massive rigid structure which fell on the floors beneath it, disintegrating one floor at a time with comparatively little resistance.
Many conspiracy theorists have also mentioned that the burning temperature of jet fuel is lower than the melting point of steel, so additional factors MUST have contributed to the collapse. However, these theorists fail to realize that at greatly elevated temperatures (such as those created by burning jet fuel), steel weakens significantly (even without melting) and collapse is a possibility.
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