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  • This is a hole on top of the Shanghai World Financial Center.

  • This is a 660-ton steel ball hanging inside of Taipei 101.

  • And these are massive clockwise balconies on the Burj Khalifa, the tallest building ever made.

  • These design choices might seem like gimmicks to give these skyscrapers their iconic looks.

  • But behind each feature is a brilliant engineering trick designed to one thing: Confuse the wind.

  • Wind can cause a bunch of issues for buildings: broken windows, structural damage, and discomfort for the people inside.

  • And today's super-skinny skyscrapers have to deal with a particular wind-induced phenomenon called vortex shedding.

  • This happens when wind flowing past a building creates vortices, strong swirls of air that magnify the damaging effects of wind.

  • In low winds, these vortices cancel each other out.

  • But in higher winds, they create alternating low pressure zones that make the building rock back and forth.

  • As the wind speed increases, so does the intensity of the back and forth movement.

  • Every object also has its own natural sway frequency and when that matches with the frequency of vortex shedding, it creates a dramatic spike in the intensity of swaying.

  • On the top floors of a high rise, that kind of swaying can be nauseating, plus it can damage the integrity of the building.

  • But architects have an arsenal of tricks to reduce movement.

  • The first one?

  • Tapering.

  • The higher up you build, the stronger the wind force gets.

  • So to reduce surface area where the wind is stronger, designers can simply make a building skinnier as it gets taller.

  • They can do that with tapering, like The Shard in London or with periodic setbacks, like the Willis Tower in Chicago.

  • Then, designers can soften edges.

  • Hard edges aren't good on wind, so you'll often see skyscrapers with round corners.

  • But architects can achieve a similar effect with small cutouts from the edges.

  • Take Taipei 101, for example.

  • The building was originally designed with square corners, but when a scale model was tested in a wind tunnel, the designers saw a lot of swaying.

  • Here are the results after designers added sawtooth corners.

  • They reduced movement by 25 percent.

  • The next option is pretty simple. You can just open it up with holes.

  • Skyscrapers like Saudi Arabia's Kingdom Centre and Shanghai's World Financial Center do this with a single gap up top, allowing wind to pass right through where it's blowing the strongest.

  • But 432 Park Avenue in New York achieves this effect with several double-floor cutouts that allow wind to pass through along the length of the entire tower.

  • There's also twisting.

  • This wind resistance technique makes for some of the most stunning skylines today.

  • Dramatic spirals redirect the wind, guiding it upward and off of the building.

  • That's the same wind resistance trick used by some industrial chimneys and car antennas.

  • Corkscrew shapes like this were impossible to build until fairly recently, thanks to advancements in software and material science.

  • And they're also promising from a sustainability perspective.

  • During the design process on the Shanghai Tower, for example, adding the iconic twist reduced the wind load by 24 percent, saving developers $58 million in structural material.

  • Finally, there's the technique so good it's invisible: damping.

  • Dampers are mechanisms designed to absorb the energy from a building's movement, counteracting the effect of the wind.

  • Skyscrapers do this in two major ways.

  • First are slosh tanks: these are containers filled with several tons of water.

  • The water sloshes back and forth, and its weight displacement helps keep the building from swaying.

  • Second are tuned mass dampers: massive weights suspended in the middle of a building.

  • These were traditionally hidden away in building design, placed on empty floors along with other technical equipment.

  • But they don't have to be. Taipei 101's tuned mass damper has been a popular tourist attraction since it opened in 2004.

  • They even have a mascot for it: Damper Baby.

  • It's a little weird.

  • These shapes, holes, and counterweights form a secret design language hidden inside of our skylines.

  • And as more people move out of rural areas and into urban ones, skyscrapers will keep getting taller and skinnier.

  • These technologies are what's making that future possible and letting us keep building into the sky.

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This is a hole on top of the Shanghai World Financial Center.

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