00:00In 1956, architect Frank Lloyd Wright proposed a mile-high skyscraper.
00:12It was going to be the world's tallest building, by a lot,
00:16five times as high as the Eiffel Tower.
00:20But many critics laughed at the architect,
00:23arguing that people would have to wait hours for an elevator,
00:26or worse, that the tower would collapse under its own weight.
00:30Most engineers agreed, and despite the publicity around the proposal,
00:34the Titanic Tower was never built.
00:37But today, bigger and bigger buildings are going up around the world.
00:42Firms are even planning skyscrapers more than a kilometer tall,
00:46like the Jeddah Tower in Saudi Arabia, three times the size of the Eiffel Tower.
00:51Very soon, Wright's mile-high miracle may be a reality.
00:56So what exactly was stopping us from building these megastructures 70 years ago?
01:01And how do we build something a mile-high today?
01:05In any construction project, each story of the structure
01:08needs to be able to support the stories on top of it.
01:11The higher we build, the higher the gravitational pressure from the upper stories on the lower ones.
01:17This principle has long dictated the shape of our buildings,
01:21leading ancient architects to favor pyramids with wide foundations
01:24that support lighter upper levels.
01:27But this solution doesn't quite translate to a city skyline.
01:31A pyramid that tall would be roughly 1.5 miles wide,
01:34tough to squeeze into a city center.
01:36Fortunately, strong materials like concrete can avoid this impractical shape.
01:43And modern concrete blends are reinforced with steel fibers for strength
01:47and water-reducing polymers to prevent cracking.
01:51The concrete in the world's tallest tower, Dubai's Burj Khalifa,
01:56can withstand about 8,000 tons of pressure per square meter,
02:00the weight of over 1,200 African elephants.
02:04Of course, even if a building supports itself,
02:08it still needs support from the ground.
02:10Without a foundation, buildings this heavy would sink, fall, or lean over.
02:15To prevent the roughly half a million ton tower from sinking,
02:19192 concrete and steel supports, called piles,
02:24were buried over 50 meters deep.
02:27The friction between the piles and the ground
02:29keeps this sizable structure standing.
02:31Besides defeating gravity, which pushes the building down,
02:36a skyscraper also needs to overcome the blowing wind,
02:39which pushes from the side.
02:42On average days,
02:43wind can exert up to 17 pounds of force per square meter on a high-rise building,
02:49as heavy as a gust of bowling balls.
02:52Designing structures to be aerodynamic,
02:54like China's sleek Shanghai Tower,
02:56can reduce that force by up to a quarter.
02:59And wind-bearing frames,
03:01inside or outside the building,
03:03can absorb the remaining wind force,
03:05such as in Seoul's Lotte Tower.
03:08But even after all these measures,
03:10you could still find yourself swaying back and forth
03:13more than a meter on top floors during a hurricane.
03:17To prevent the wind from rocking tower tops,
03:20many skyscrapers employ a counterweight weighing hundreds of tons,
03:24called a tuned-mass damper.
03:28The Taipei 101, for instance,
03:30has suspended a giant metal orb above the 87th floor.
03:34When wind moves the building,
03:36this orb sways into action,
03:38absorbing the building's kinetic energy.
03:41As its movements trail the towers,
03:44hydraulic cylinders between the ball and the building
03:46convert that kinetic energy into heat
03:49and stabilize the swaying structure.
03:52With all these technologies in place,
03:54our megastructures can stay standing and stable.
03:58But quickly traveling through buildings this large
04:00is a challenge in itself.
04:03In Wright's age,
04:04the fastest elevators moved a mere 22 kilometers per hour.
04:08Thankfully, today's elevators are much faster,
04:11traveling over 70 kilometers per hour,
04:13with future cabins potentially using frictionless magnetic rails
04:17for even higher speeds.
04:19And traffic management algorithms
04:21group riders by destination
04:23to get passengers and empty cabins where they need to be.
04:28Skyscrapers have come a long way
04:29since Wright proposed his mile-high tower.
04:32What were once considered impossible ideas
04:35have become architectural opportunities.
04:38Today, it may just be a matter of time
04:40until one building goes the extra mile.
04:43How do engineers ensure that these massive structures
04:47don't come down in an earthquake?
04:49Check out this lesson
04:50and learn why it's not the sturdiest buildings,
04:53but the smartest that remain standing.
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