The majority of debris fell onto itself. Of course when you have something big that collapse debris is going to go everywhere, but most of it fell straight down. A bunch of floors failed and fell straight down on top of the next floor causing it to collapse.
The outside parts of the building went out, which happen to be mostly outside scaffolding/glass/window framing, etc. But the floors sat on trusses connected to the underside support structure of every floor. Meant to support ONE floor each. Maybe two floors could have been supported by the trusses. But it wasn’t enough to hold the top third or so of the building. 5 or so compromised floors failed, and dropped on top of the next floor in line. Which made the next floor in line fail faster and faster.
If you watch, you can literally see it happen. Top of South Tower goes like this:
1.) debris goes outward from those damaged floors falling.
2.) half second or so pause.
3.) then the South Tower falls.......top down
The reason you don’t know what happened is because you haven’t seen it happen before. You’ve only seen explosives destroy. Since that’s what you’ve seen mostly, you know for sure it wasn’t explosive. Good enough for me.
I've witnessed reinforced concrete “destroyed” two ways, extreme pressures such as hammers and penetrators that leave the concrete destroyed structurally but generally left as its components as the gravel and such...and explosively to induce the speed of sound though the concrete and particulate it which requires explosives with speeds over 3200 meters per second. That will turn concrete and all its components into a fine powder.
I can't comment on why the building fell down, but what happened during and after I can have my own poorly informed opinion about.
The metal floor pans on each building were filled with almost a ft/acre each of reinforced lightened concrete. Thats almost 110 acres of concrete, each building. How did the 500,000 ton building in the act of falling, create enough energy to grind to a particulate mostly all of this concrete so fine it founted like Vesuvius and coated the surrounding area with up to 6 inches of the material that once resided in the falling “pancakes” as solid concrete.
To accomplish this with explosives some have estimated it would require about 2-300,000 tons per building.
See my dilemma? Leaves the conspiracy guys with a real problem, too. My eyes and limited experience allows me to opine it was blown to kingdom come, from the top down, 10 or more floors at a time, yet it would take probably 2-300,000 “tons” of explosives to do so. What energy other than the force of gravity on a falling object was present to make that much material capable of blowing away on the wind?
Therein lies the rub. Hard to hide 300,000 tons of really high explosives in 500,000 ton buiding, isn't it?