I was wondering this earlier today. If the towers had been damaged not quite bad enough to actually collapse on their own but teetering"on the brink" (say 98% of the way to full collapse) would we have been able to bring them down in a controlled fashion without destroying adjacent buildings in the process? Additionally, how do you set up a controlled demolition on buildings that massive that would have been too unsafe to really work around, let alone inside to place charges?
I’m thinking that the area around the WTC was so dense that there wouldn’t have been any way to demolish the buildings without putting the demolition crews lives at great risk. Even then I don’t know how we would have brought them down in any sort of controlled fashion.
I could swear that Cecil Adams wrote a column on this question, but I can’t find it. Anyhow, David Macaulay wrote a book called Unbuilding that imagined how you would disassemble the Empire State Building. (The idea is that it’s to be rebuilt overseas, so it’s not a demolition project.) Basically, his idea is that you’d start at the top and reverse the building process. Presumably some of the structure could be lowered in the elevators, although you’d probably need a tower crane to disassemble and lower the structural steel. So you wouldn’t do a controlled demolition, although some quite large buildings have been taken down that way.
The techniques of controlled demolition using explosive charges are sophisticated. Crews aren’t nearby (nor is anyone else) - they fix charges and then back way off before setting them off. If the buildings are strong enough to withstand people walking near their base, charges can be safely placed. (If they aren’t, they will collapse on their own on the next windy day.)
YouTube has lots of videos of controlled building demolitions (sample). It’s often impressive how little problem this creates for nearby structures.
Controlled demolition is out, since it’s illegal in the City of New York (There might have been a waiver, but I don’t know if the city would have been willing to grant it).
If I wasn’t clear I’m asking about the towers being in the same shape they were in just before they finally gave way. I’m sure there was no chance of elevators or stairs past a certain point. And thing were likely VERY unstable so I’m not sure how you could safely put someone inside to place charges even if it was legal.
I was thinking maybe work off some sort of super cranes or something on top of nearby buildings? Hook up giant blimps to the top to keep them from crashing down while being disassembled?
They would have to reinforce the buildings first, from the ground up, to make them stable enough to disassemble from the top down. And no way is a controlled explosive demolition going to be done on buildings of that size in that limited space.
Even if they had the space to do a controlled demo job on it, I doubt that it could be done considering the damage to the upper floors. In a controlled demo, the building collapses into itself, but with as much damage as was done to the upper floors of the WTC buildings I would think that trying to control where the upper stories fell would be a crap shoot.
There was actually a thread similar to this a few months ago.
Anyway, a slight hijack (no pun intended) - one thing I’ve wondered about is what would have happened if for whatever reason (the flight was delayed, they crashed before making it, they overshot the building, etc.) the terrorists had failed to hit the second tower, but the first one still got hit and ended up collapsing.
Would there have been any way to salvage it? Or would the debris from the one tower falling have damaged the other building beyond repair or messed up the foundation to the point where it was no longer sound?
There was a case in Quebec a few years ago where someone in a small plane hit a TV tower. IIRC aircraft and body had to stay embedde up there for several days while the authorities determined if the tower was even safe to be near, let alone climb.
That would be the situation, I suspect. Nobody would be expected to climb or go near the buildings, inspections would likely be done from a distance with helicopters and hi-res cameras; followed by building inspections from the top down by helicopter if it seemed stable. All the while, anything within 2,000 feet would stay evacuated.
If the buildings were too unsafe, then they would likely be blasted down by volunteers. I wounder if they would alternatively try to build a parallel steel framework around or alongside to steady them and allow for top-down demolition. A 100-story open-frame ironwork would probably not be as big an effort as a full repalcement building. could be done in a few months, and footings would consist of just filling the base area all the way down with solid concrete.
I assume if the buildings were “marginal” then the biggest issue would be bracing them to stop any swaying that might create failures. Either you build a framework 80 floors high between the towers, or you weld brace pieces across the holes and weakened columns. Then you have something strong enough to allow top-down demolition or full-scale rehabilitation, whatever is cheaper. The guys doing the brace welding or scaffold building would probably be volunteers paid a huge amount and with a massive contingency payment to their widow.
How did they demolish the Windsor Tower in Madrid?
But charges are not placed only near the base in a controlled demolition. The charges are placed inside, and on almost every floor. The building probably would not have been safe enough for that.
I can’t imagine anything than a controlled, explosive demolition being used, even if the demolition setup isn’t as thorough as in an ideal scenario.
Dismantling from the top down requires months and a building 98% of the way to collapsing is going to fall down in the first strong wind storm. Nobody is going to prefer an uncontrolled collapse at an unpredictable time when they can have a partially controlled collapse at a known time.
Knowing the time would let them evacuate the area, board up windows, set up barricades, etc. that would minimize damage to nearby buildings and to pedestrians.
They take out the centre support, and the two sides collapse in. This is usually a rectangular building. Oddly, The WTC7 did this perfectly since the central lobby featured a “weakest link” and collapsed first. The ends fold into the middle, so debris goes inward rather than outward.
For items much taller than wide, they try to find a clean direction to drop the building - since it’s usually impossible to do the “interior fold” when a building is shaped like a tall thin tower. Perhaps the logical thing would be to take out a northwest corner of each tower and try to topple it in the gap of the northbound west side highway. I don’t know if they can aim a building that well. It would be expensive if they missed - but the world trade centres gone would be expensive anyway; what’s another 30-storey building compared to that?
I doubt that anyone could purposely drop both towers vertically. You can see when one tower started to go it was leaning, we can only speculate on the feedback mechanism that kept it upright (the low corner hit first, encountered the most resistance, so slowed and straightened?) I’m not sure much more damage could be avoided by deliberately dropping them the same way they actually fell.
This too would require explosives all through the upper floors; basically, setting massive explosives in the weakest part of the building, where the airplane-shaped holes were. Then what? Lay 1000 feet of cable down the building to trigger the blast with, or trust a radio detonator?
Whereas every brace you weld into place would make the building that much more stable until you could do a top-down demolition. I wonder if some bright boy would have suggested that they could make a pair of 60-storey towers out the remains and saved a lot of money all around? According to stories of the camp in Afghanistan, even the engineer Bin Laden did not expect the towers to completely collapse; at most he expected the top third to topple off.
Yes, it’s possible the building could have supported itself, but not the additional weight of a few workers placing charges.
I think dracoi has it right: You analyze the situation, place as many demolition charges as you think are consistent with safety and minimizing damage to nearby buildings, evacuate the area, detonate the charges, and deal with the results (which probably will include some “collateral” damage). An imperfect solution, but substantially better than the alternatives.
the meridian tower in phila. was shored up and brought down floor by floor after the fire. the fire floors had to be stablized first before they could start deconstruction.
they ran freight like elevators on the outside of the building. took quite some time as well.
I’m not sure how much damage was done structurally to the buildings below the impact points. I could picture them temporarily condemning them and the surrounding areas, assess the structure, and then use various methods to decrease the live load of the damaged portions (shoot out the windows and then use solo men to push as much weight out the windows. Desks, files, computers, furniture, etc. everything that’s not part of the structure). You could even use copters to lift heavy equipment off the roof.
Once it’s light enough and structurally sound enough it’s a matter of dismantling the damaged portion piece by piece either dropping pieces or lifting them away by copter.
After that you could cap them off at that level or attempt to rebuild.