Not sure why I think about such things but anyway,
If the airplanes had struck the towers higher up and the resulting collapse was not heavy enough to continue all the way to the ground, leaving a pile a debris at the top of the towers. How would the clean up of the debris have been done?
I can’t imagine it could have been done safely from below and would not the surrounding area (blocks?) have to have been cordoned off (months, years?)because of the possibility of stuff falling off the top whenever the wind blew and the building moved?
Even if it didn’t knock down the towers immediately, it’d probably compromise them to the point where they couldn’t be trusted. They’d salvage whatever of value they could, then evacuate the vicinity for safety and do a controlled demolition that would end up looking a lot like the uncontrolled one did (there’s really only one way a tower like that can go down).
Suspect they would have had to bring them down in a controlled explosive demolition, unless you actually changed the structure radically. Maybe in a controlled demolition, larger /expensive structures like WTC 7 and the undergrounds could be saved.
If you meant that the WTC 1 and 2 actually had larger load margins, eg they were made of reinforced concrete , then perhaps they could have the tops demolished bit by bit top down ( by careful cutting ? or by using explosives even )… And even have damage repaired. (eg new tops built on the bottoms! )… But your question said the top only just avoided pancaking the bottoms, as in low margins, just not so low that the runaway pancake process occurred, so this was already excluded.
The WTC 1 and 2 had load margin of 2. This means that at each floor, the structure was only strong enough to hold at most TWICE the load above.
Now with some damage to the structure at (or near) a floor, the result of the damage easily be that the floor is unable to hold 1 times the load above… that is where it becomes too weak. it fails. So a load margin of 2 is not very much. Reinforced concrete structures have a much larger load margin. WTC 1 and 2 were unique like that. Normally only metal sheds like factories and hangars, or antenna towers, have such a low load margin
I am going on about load margin because that is why , even if WTC 1 ,2 didn’t collapse at the time, they would have had to be demolished due to the damage of the planes and fire.
IANAStructuralEngineer, but I would imagine that, what with the towers being relatively much weaker and far less solid than a tree, there’s no way they could hold together and topple over lengthways. At worst I would have thought they’d start to angle over at the base and then just fold in on themselves and fall straight downwards, albeit rather less “tidily”.
A tree falls over because its roots or lower trunk fail, creating a pivot point near the ground.
For the WTC to have fallen over like a tree, it would have needed a similar pivot point near the ground. As I recall, when one of the towers started its collapse, the section above the impact point did in fact start to tip over a bit, but it didn’t tilt very far before pancaking on the section below the impact point. Had the impact point been much lower, the upper part would have been taller and might have been able to pivot farther over, possibly causing greater damage to adjacent buildings.
Conspiracy nuts would have popped up immediately claiming that planes didn’t really strike the WTC because, if they had, the towers would have collapsed.
As I recall, the 1993 WTC bombing was fairly near to one of the building’s corners. If the blast had been more powerful, wouldn’t the localized break have created such a pivot point?
I would guess so. If it starts falling over, it’s unclear whether the entire building would hold together during the entire descent to ground. There are significant stresses created during that pivoting action: gravity wants to pull everything downward at the same acceleration rate, but the base is barely moving, so later in the swing the top is accelerating downward much faster than 32 fpss, and so on. Consider this chimney demolition video, with detonation at 0:23. As it falls over, it starts to deform from its straightline shape. That chimney was steel-reinforced concrete; the disintegration is even more dramatic for brick chimneys, which have almost no tensile strength. The WTC towers were made with lots of steel to tolerate significant wind loads, but I have no idea how they would have behaved during a tipover.
The Alfred P. Murrah building in Oklahoma City had much less damage than the WTC, and it was eventually demolished by a controlled explosion. Here’s an aerial view of the damage.
The buildings would not have been repairable, and would have been brought down.
This actually is one of those times a fairly simple, at-home experiment helps visualize something regarding 9/11.
Take a cardboard paper towel roll. Stand it on its end. Balance some heavy books on top.
The tube structure can tolerate a LOT of dead weight. The WTC towers took advantage of the tube.
Now, remove the books, and lay the roll down on the floor. Put books on it. It will not support the weight, of course, that it would before. It collapses flat.
The WTC towers couldn’t “topple” like a concrete chimney does. There’s just not enough structural design present to resist THAT load in THAT direction. The top block of one tower did, indeed, topple over a bit before being obscured in smoke and debris, but it would have disintegrated at that angle whether or not it impacted the floors below.
A controlled demolition is what I assumed would be the only way to do it, but still leaves me with the question of how all the prep work would be done with the possibility of steel or concrete or whatever falling at anytime.
And perhaps a bigger question is who would take on the task of doing that demo work, I mean with our litigious society you can be sure their would be numerous lawsuits over every aspect of the explosion and the aftermath. Hard to imagine any insurance company willing to take on that and give the ok to set off the charges.
The other problem is that a lot of the controlled demolitions you see are concrete pillar buildings. Demolition is easy - drill into the pillars, and the charges will crumble enough of the pillars to destroy the strength of the building. How easy is it to destroy structural integrity of stel I-beams?
it seemed to me from the news footage that the lean in the tower collapse was self-correcting. If one side or corner statrs to lead, that has less impact than the flat whole floor. The leading edge will be delayed until the rest of the building catches up,
The upper floors would have been removed by the use of cranes and the remainder of the buildings would have been leveled by controlled demolition.
The upper floors would be too unsafe for workers to be inside to do the prep work necessary for a controlled demolition so they would have used cranes and man-baskets with ironworkers and cutting equipment to remove large sections and lower them to street level after stabilizing it to prevent collapse.
Linear shape charge cutters are used. You attach them to the side of the beam, and when the shaped charge goes off it forces the deformable copper liner on the inner surface of the shape charge through the beam like a supersonic guillotine.
The challenge would be placing the charges on the damaged section of the building and the structurally unstable parts above it without accidentally triggering an uncontrolled collapse in the process. You’d hypothetically have a building that was damaged not quite badly enough to collapse. Judging just how far from collapse it is on its own will be tricky and very important to get right.
