Interesting column. For a great illustrated book on the painstaking process of disassembling (and not just destroying) a skyscraper - the Empire State Building, no less! - see Unbuilding by David Macaulay: Amazon.com
Watched them slowly dismantle a @ 30 story building in downtown Minneapolis a few years ago. Quite certain it would be a different process for taller buildings and ones without large surrounding lots, as they had a small bobcat up in it, breaking down the inner walls and then pushing the debris over the side into the parking lot below. A crane was used to bring down large sections of steel as they cut them apart.
China is going to have a helluva problem with this in the long run.
(Article from 2010)
*“Every year, new buildings in China total up to 2 billion square meters and use up 40 percent of the world’s cement and steel, but our buildings can only stand 25 to 30 years on average,” Qiu Baoxing, vice-minister of housing and urban-rural development, said at a recent international forum on green and energy-efficient building.
This means the average life span of China’s residential buildings is shorter than their intended life span of 50 years at the blueprint stage. As a result, property developers have been urged to extend the median life span of buildings.
*
Cecil talks in the column about several nations having innovative techniques in demolishing skyscrapers, the South Africans, French, Japanese. He might have mentioned that the Saudi Arabians too have shown considerable expertise in this area. 
Too soon! 
Pretty cool demonstration of how to collapse a skyscraper.
They did something similar to unbuild the 41 story Deutsche Bank Building in Lower Manhattan after 9/11.
I disagree with the 50 year lifespan though. That seems very short, even if the foundation is flooded with water. Maybe older masonry and concrete skyscrapers as that can crumble and erode. But modern glass and steel skyscrapers have their foundations embedded in bedrock and wouldn’t rust that quickly.
“Modernizing” a skyscraper is more about the interior design, keeping the exterior façade clean and updating systems like HVAC, elevators or electrical. It’s not like they are in a constant struggle to keep the structural integrity so they don’t collapse.
I would imagine there is some maintenance going on to prevent just that. I remember reading in The World without Us the old country saying, “If you want to take down a barn, cut an eighteen-inch hole in the roof and stand back.” A skyscraper is more substantial than a barn, but the same thing applies.
In all fairness, designing skyscrapers for when humans are no longer around to take care of them was not something we covered when I was getting my BS in Civil Engineering. And it’s been over 20 years since I’ve done anything remotely related to structural engineering professionally.
But, here is a thought experiment that should demonstrate the difference between a skyscraper and a barn. Take a steel beam and a wooden beam, approximately the same size and cross section. Leave them outside for a year (for our purposes, assume somewhere in the Northeast USA which has seasons and weather). What will they look like at the end of the year?
The wood beam (depending on factors like how it’s treated), will probably be a bit rotten and invested with insects, mold and fungus.
The steel beam will have a coat of rust on it.
The point being that steel does not rot through like wood. It does rust, however. A steel beem or column’s strength is a function of the non-rusted cross section.
So the calculation is really how long does it take for a skyscraper’s support columns to rust through enough that they can no longer structurally support the building? Keeping in mind that they are designed with large factors of safety, so it may be significant.
Great subject, now I know.
The answer was interesting but I was kind of disappointed it was more about planned tear down than how long would a tower last if left unmaintained or otherwise mistreated by the apocalypse.
I fully understand and agree with what you are saying, but given slightly different conditions those steel beams may go a bit quicker than expected. For example, a bit of ocean level rise and those steel beams in the bottom couple of feet of the building get a permanent soak in salt water, accelerating that rusting (and electrolitic ?) deterioration. Once the base is gone it won’t matter how strong the rest of the building is. To me, this would be the sky scraper version of cutting the hole in the roof of the barn.
Or how about a bit of fire. During my days as a (volunteer) fire fighter we were trained that in a large fire wooden beams would hold strength longer than a metal beam (assuming both have equal exposure to the heat of the fire). The wooden beams would heat up, catch fire, then slowly loose strength as they burned from the outside in. But a steel beam could do two things.
One- Hold their strength until reaching high temperatures, then rapidly sag and collapse.
Two- expand, pushing out on support structures causing them to deform and collapse. This I witnessed in a couple of smaller buildings (not many sky scrapers on the prairie).
Thus the rule that we would never enter a metal structure building to fight a large or long-lasting fire. Strictly wooden structures were open to evaluation.
You’re right that it would happen much faster if the base was soaking in salt water. I just don’t know how fast.
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Skyscraper fires usually don’t get that hot. 9/11 was an unusual case as the fire was fueled by jet fuel. Of course, with no occupants and no electrical power, you eliminate a lot of potential causes of fire.
I hear there’s one in Kansas City that’s seven stories high.
It’s said that the highest point in Nebraska is the top of the Capitol Building in Lincoln …
It may seem like it, but…
*The highest point in Nebraska is Panorama Point, at 5,424 feet above sea level. The lowest point in Nebraska is 840 feet above sea level at the Missouri River in southeastern Richardson County. *
That’s a pretty good difference in elevation. Far more than the 1,699’ difference between highest and lowest in Minnesota, where I live.
Loved that book! Quite fascinating.
hmmm… I think I’m missing a specific reference. After all, Kansas City (Missouri) has quite the sky-line. Could you enlighten me so I can learn and enjoy.
Ah yes, the “Penis of the Plains”. Actually quite the building architecturally and artistically. Stone clad steel structure. Another variation on the “how long would it last”. The worst mother nature could throw at it would be a tornado, or a fault line something like 75 miles away. Although all the hot air from the politics might keep it upright longer than expected.
I grew up in Lincoln and was always told the local laws forbid the building of tall buildings that would obstruct or distract from the view of the capitol building.
The tallest building in South Dakota is 11 stories.
CenturyLink Tower (formerly Qwest Tower) is a 296,448 sq.ft office building located in downtown Sioux Falls, South Dakota. It is 174 feet tall and has 11 stories, dominates the skyline of Sioux Falls, and is the tallest building in the state of South Dakota. Previously the 202-foot Zip Feed Tower was the tallest building in Sioux Falls, as well as South Dakota.
The musical “Oklahoma,” I believe. Everything’s up to date in Kansas City, they’ve gone about as far as they can go…