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How do Skyscrapers Keep Defying Gravity?

 It seems that with every passing year, skyscrapers are getting taller and taller, as companies, cities and countries try to outdo each other with greater and more breathtaking constructions. Yet, building such giants is far from easy. It’s not only a question of finance, materials and time, it also requires ingenious solutions to combat the problems that come from aerodynamics, safety and weather.
 

In this post, we are going to look at just what the problems that face skyscraper building are, and how these issues are being overcome.

 
The dangers
Perhaps the most important issue for engineers to overcome when designing and constructing tall buildings is the effect of strong winds on the skyscraper at high altitude. If a building has not been well designed, winds and sway can cause terrible damage.

As winds increase in speed, little pockets of air known as eddies collect on the side of the building opposite the wind flow. When the eddies grow, and increase in power, their subsequent oscillations disturb the consistent air flow, leading to something called 'vortex shedding'. 

Vortex shedding is when the two identical eddies are in turn ‘shed’, allowing new air to rush into their place, which brings additional oscillations of air pressure.  
If the frequency of this shedding matches the frequency of the building’s vibration, the building will sway. Depending on how well the structure has been conceived and built, this swaying could topple the skyscraper.

Solutions
A common solution to this devastating event is known as 'dampening'. This is when engineers make modifications to the building’s joints in order to ‘dampen’ the energy build-up from the wind.

For instance, Taipei 101 (formerly the world’s largest building) is fitted with a 730-metric ton mechanical damper inside. This damper is tuned to the same resonance as the building and sways in the opposite direction, reducing the sway factor.
 

However, not all buildings use the same solution. The current world record holder, Burj Khalifa, Dubai, is instead constructed so that no vortices can occur. Because the structure is not built uniformly, air flow is disrupted in such a way that no eddies or vortices can become organized enough to make a difference.
 

The building has a Y-shape plan, with each higher tier slightly rotated from the lower one, making a spiral effect. Each floor is also smaller than the previous one. Countless computer models and tunnel tests were conducted to examine the consequences of the aerodynamic principles involved.

So, thanks to clever engineers' better understanding of aerodynamic physics, and the prestige to be gained from creating the tallest skyscraper, many new record breakers are currently in the works. For example, Jeddah Tower in Saudi Arabia is set to be the first skyscraper to be raised 1 km into the sky. 

Just imagine the incredible views from future buildings like this! But try not to worry about the wind so much.

BONUS: How to Build Higher and Higher

H/T: sciencealert.com
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