On this page, and three subpages, we look a little more closely at what happens during a gravity-driven collapse of the towers, to understand all the reasons why it would not complete in near-free-fall time if at all.



Like the simplest argument about free-fall this is still an intuitive argument, but the purpose here is to get an overview of all the significant things that would be happening during a collapse which would slow down the process and soon stop it altogether.



On the page about the Tower Structure we learned that the core columns of the towers were designed to hold most of the vertical load (about 60%), while the perimeter columns mostly resisted lateral and twisting forces (and about 40% of vertical load).

Note that, for these pages, I am going along with the assumption that, after the planes crashed and exploded, the fire caused parts of the steel structure to weaken and fail. (This will turn out to be a false assumption, but it is more complex to understand why.)



How the collapse was initiated, is not relevant to the question of where the energy comes from to continue the collapse. (see Collapse Theories - Theories Purport to Explain the Unexplainable)



I will often describe the fall of the towers as a "collapse" but you should take that to mean, "assuming they could have collapsed by gravity alone".

much simpler task of disproving that theory

Collapse Follows Path of Least Resistance

If the upper floors started to tilt, as we saw in both towers, the rotation should continue, following the path of least resistance, until they topple over, thus stopping the collapse.



Collisions Require Time and Energy

Even if a vertical collapse got started, the collision at each floor takes some amount of time to crush the steel and concrete, but in a free-fall collapse, there is NO time to spare. Each collision not only takes time, but it uses a lot of energy to crush the materials.





Ejection of Debris Requires Energy and Slows Collapse

Not all the destroyed floors and columns accumulated in the fall straight down.



In fact, we saw huge amounts of debris, including steel beams and finely pulverized concrete, being ejected out at high velocity throughout the collapse, which requires energy and therefore reduces the energy of the falling floors.



Any mass not falling straight down will reduce the energy of the falling floors, and therefore slow the collapse.

The top toppling over rather than falling straight down. The destruction of the steel and concrete structure of each floor, and the accumulation of debris, which reduces the speed and energy of falling floors. The ejection of debris mass at high velocity that is therefore not falling straight down.

No steel structures have ever collapsed to the ground due to fire damage before or after 9/11. And yet this supposedly happened not only twice in the same day, but three times. Another building, WTC-7, a 47 floor tower that had only a few small fires, collapsed 7 hours later in a more classical controlled-demolition style, removing the bottom support so the top can free-fall down.

In a. It is agreed by most people that the jet fuel was mostly burned up within the first 20 minutes, and the spreading fires may have softened some of the steel and added some heat, but this was a small factor compared to the energy required to collapse the towers. More on the fires later.During a collapse, many things are happening, and a very complex analysis is required to try to show that ithave actually been a gravity-driven collapse. But we have abecause we only need to show how it could not be true. Each of the following points is enough to severely weaken the official story of a gravity-driven collapse. The combination of all of them adds up to impossibility of collapse due to gravity alone.So what does all this mean? Since the towers fell in nearly free-fall time (which almost everyone agrees to) this requires that the falling floors must continue accelerating as if there was, as if the mass and structure of the towers were not there at all.That means thatTo rationalize the near-free-fall time, Bazant and other defenders of the official story give their twisted jumbled mess of an argument, which I suspect is intentionally obscure to hide the flaws. Bazant tries to make it look complex, but it is really very simple. Just remember thatduring the collapse for any of the causes described on this page.Given all those losses of mass, speed, time and energy, it should be much clearer now why a gravity-driven collapse would have a very difficult time completing in near-free-fall time, assuming it got started at all. Subpages linked above and in the panel on the left examine each of these points in more detail.