IELTS Listening Online – Sample 4

1   pyramid

2   piles

3   aerodynamic

4   metal orb

5   friction

Will there ever be a mile-high skyscraper?

In 1956, architect Frank Lloyd Wright proposed a mile-high skyscraper. It was going to be the world’s tallest building, by a lot – five times as high as the Eiffel Tower. But many critics laughed at the architect, arguing that people would have to wait hours for an elevator, or worse, that the tower would collapse under its own weight. Most engineers agreed, and despite the publicity around the proposal, the titanic tower was never built. 

But today, bigger and bigger buildings are going up around the world. Firms are even planning skyscrapers more than a kilometre tall, like the Jeddah Tower in Saudi Arabia, three times the size of the Eiffel Tower. Very soon, Wright’s mile-high miracle may be a reality. So what exactly was stopping us from building these megastructures 70 years ago, and how do we build something a mile high today? 

In any construction project, each story of the structure needs to be able to support the stories on top of it. The higher we build, the higher the gravitational pressure from the upper stories on the lower ones. This principle has long dictated the shape of our buildings, leading ancient architects to favour pyramids with wide foundations that support lighter upper levels. But this solution doesn’t quite translate to a city skyline as a pyramid that tall would be roughly one-and-a-half miles wide; tough to squeeze into a city centre. 

Fortunately, strong materials like concrete can avoid this impractical shape. And modern concrete blends are reinforced with steel-fibres for strength and water-reducing polymers to prevent cracking. The concrete in the world’s tallest tower, Dubai’s Burj Khalifa, can withstand about 8,000 tons of pressure per square meter; the weight of over 1,200 African elephants! 

Of course, even if a building supports itself, it still needs support from the ground. Without a foundation, buildings this heavy would sink, fall, or lean over. To prevent the roughly half a million ton tower from sinking, 192 concrete and steel supports called piles were buried over 50 meters deep. The friction between the piles and the ground keeps this sizable structure standing. 

Besides defeating gravity, which pushes the building down, a skyscraper also needs to overcome the blowing wind, which pushes from the side. On average days, wind can exert up to 17 pounds of force per square meter on a high-rise building: as heavy as a gust of bowling balls. Designing structures to be aerodynamic, like China’s sleek Shanghai Tower, can reduce that force by up to a quarter. And wind-bearing frames inside or outside the building can absorb the remaining wind force, such as in Seoul’s Lotte Tower. 

But even after all these measures, you could still find yourself swaying back and forth more than a meter on top floors during a hurricane. To prevent the wind from rocking tower tops, many skyscrapers employ a counterweight weighing hundreds of tons called a “tuned mass damper.” The Taipei 101, for instance, has suspended a giant metal orb above the 87th floor. When wind moves the building, this orb sways into action, absorbing the building’s kinetic energy. As its movements trail the towers, hydraulic cylinders between the ball and the building convert that kinetic energy into heat and stabilise the swaying structure. 

With all these technologies in place, our mega-structures can stay standing and stable. But quickly travelling through buildings this large is a challenge in itself. In Wright’s age, the fastest elevators moved a mere 22 kilometres per hour. Thankfully, today’s elevators are much faster, travelling over 70 km per hour with future cabins potentially using frictionless magnetic rails for even higher speeds. And traffic management algorithms group riders by destination to get passengers and empty cabins where they need to be. 

Skyscrapers have come a long way since Wright proposed his mile-high tower. What were once considered impossible ideas have become architectural opportunities. Today it may just be a matter of time until one building goes the extra mile. 

Source: TED Ed – By Stefan Al

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