After seeing the destruction caused by the collapse of the WTC, I started to wonder how such a structure would actually be brought down whenever it reaches the end of its design life. With smaller skyscrapers, you can just implode them. But the WTC imploded just as if it had been demolished, yet the destruction that caused was massive.
The WTC had something like 10 levels below ground with shopping malls, a train station, etc. None of that could have survived an intentional demolition.
Do the engineers of such huge structures have to come up with an eventual demolition plan? Or do they design them to stand forever? It seems to me that almost every building eventually comes down.
I can’t say I know the answer. At 439 feet, the [J. L. Hudson Department Store](http://www.controlled-demolition.com/cdi.html#J.L. Hudson Department Store), formerly of Detroit, holds the record for tallest building brought down with explosive demolition. If I read correctly, it was 29 stories above ground and 4 below.
Here in Houston, when the time came for the 24 story Bank of the Southwest building (relatively modern - 1956) to come down in the early '80s they took it apart, piece by piece. It took quite a bit of time.
No buildings are ever imploded. Rather, a series of controlled explosions cause them to collapse.
As for the WTC, while it looked like it was collapsing similar to buildings being intentionally demolished, it was probably the shape of the towers that lead to most big pieces simply falling straight down. The video footage only shows the top of the buildings; after that collapsed I’m guessing there would have been much more outward motion towards the bottom, thus causing the severe damage to the other buildings.
Well, I don’t know… That is one hell of a lot of mass coming down. They were saying that just the shock of the building hitting the ground would have damaged the foundations of the surrounding towers.
Would it have been possible to just dismantle the towers, floor by floor?
I imagine the Sears tower and other mega structures have similar problems. The question remains - do the original architects design the buildings with a demolition plan in mind, or do they just design them to stand forever? The latter seems a little…wishful. There are lots of natural and manmade disasters that could disable a building and leave it useless - fires that weaken the structure, aircraft collisions, other terrorist attacks, earthquakes, or just economic or societal changes that make the building cost-prohibitive to maintain.
In David Macaulay’s wonderful book Unbuilding, the Empire State Building is demolished. The (tongue in cheek) premise is that a Saudi oil magnate purchases it for his headquarters and wants to move it to Saudi Arabia, but they only save and ship the pieces “necessary to restore its appearance”, i.e. the facade, so I assume the general outline of the demolition process is correct.
Wreckers clear out all the interior walls, pipes, etc down to the steel frame. The rubble is sent down to ground level through a series of chutes. Steelworkers disassemble the frame, which is recycled. The pieces they cut loose are lowered to the ground by crane. It takes three years.
Very very oddly, at the beginning of the book, Prince Ali Smith, whose purchase of the Empire State Building motivates its demolition, offers to pull down the World Trade Center towers “as a goodwill gesture.” (New Yorkers, wanting to preserve a historic landmark, offer him the two WTC towers for the price of one Empire State Building.)
Here’s the guys you need to ask: http://www.controlled-demolition.com/ as they’re the ones who do it for a living. Basically, what they do is go in and examine the building, figure out how much it weighs, where the structural loads are, and the slap just the right amount of explosives on the critical supports. They push the button and it all drops down within inches of where they predicted.
Yes, but I’m not sure it works that way with something this big. I mean, even after it comes down it will still make a pile of rubble bigger than most large office buildings. CDI can make the building come down straight, but they can’t make the 6-10 story pile at the end keep from toppling over. And anyway, the energy released by such a collapse is huge, and there was a giant retail shopping complex and a major subway station under the building, which would never survived even a controlled detonation.
Sam, the WTC was the largest building to be brought down in any manner, so until last week, it was unexplored territory. I’m sure that the folks at CD could have brought it down with similar results as the hijackers had they been contracted to do the job. And you’re right about the underground structures not being able to withstand the demolition, at least not all at once. The solution to that would have been to bring the building down either piecemeal or in a slower manner. The WTC buildings both collapsed in a span of about 10 seconds, were one to try and bring a building of that size down using explosives, I imagine that the easiest way to do it that would minimize the damage to surrounding areas would be drop each floor individually. Admittedly, you’d get to a point where the weight of the floors dropping on to the ones below would be greater than the floors could bear, but that would be something that could be figured out ahead of time and planned for. Or, conversely, one could drop the lower floors and work their way up, since the building could stand without any floors at all (If I’m not mistaken.), then you could drop the outer shell last, leaving you with a huge pile, yes, but one that was at least manageable.
Tuckerfan, I’ve read accounts that speculate that the overloading of the floor structures below the collapsing upper stories is exactly what happened. The term most often used was “pancaking.”
The theories varied, but generally, the combination of heat and shock from the impacts of the airliners and the resulting fires caused the floors above the impact points to detach from the steel frames and slam downward onto the floors below, while the relatively intact steel framework beneath the impact points served to confine the collapses. From a purely technical view, the collapses resembled textbook-correct demolition of the type CDI sells.
That’s exactly what they did with One Meridian Plaza in Philadelphia. The building (38 stories, 492 feet tall) was severely damaged by a fire in 1991. After years of sitting vacant, it was finally dismantled. Philly.com has an article on it. This site has a couple of pictures taken during the dismantling.
You know, I never knew what they finally did with One Meridian Plaza after the fire. Its kind of a textbook example (well, not kind of, it just plain is) of how not to let a highrise burn. No sprinklers until the 29th(?) floor, pressure reducing valves on the standpipes that didn’t let enough water come out to stop the fire, stuff like that. On a good note, though, the building didn’t fall down. Almost did, but Newton decided to play fair for once.