Why do skyscrapers not fall over in strong winds?

Burj KhalifaCapturing our attention and imagination; skyscrapers represent the coming together of science, engineering and architecture. Combined with human ingenuity, the end results are impressive structures that reach ever higher and higher into our cities skies

Located in Dubai, United Arab Emirates, the Burj Khalifa is the tallest building in the world with a height of 828 m / 2,716.5 ft. Opened in 2010, it not only holds the record for being the tallest building in the world, but also holds a handful of other world records. In fact, the Burj Khalifa is so tall that you can watch the sunset at the bottom of the building, get into the elevator (which holds another world record) and watch the sunset all over again from the top observation deck.

Designing and building these impressive skyscrapers is a tall order because they are subjected to such immense natural forces. Take the wind, for example. At the top of the Burj Khalifa the wind speed can reach 150 km per hour / 90 miles per hour. To endure this, skyscrapers are traditionally built with the ability to move a few metres, similar to a swaying tree, to help reduce the stresses on the building. So when stood atop a skyscraper, if it feels like the ground is moving – it probably is.

A simple way to control how much the skyscraper moves is to build it with a very strong core at its centre. The Empire State building and other early skyscrapers were built with the central elevator shafts strengthened by a network of steel bars to hold the core of the building together tightly. More modern methods include having one or more concrete cores built into the centre of the building to provide a rigid centre for the skyscraper.

But due to the amazing height of the Burj Khalifa, these techniques are simply not enough to stop the building from swaying excessively.The Burj Khalifa engineers instead built the skyscraper with three wings arranged around a central core, in the shape of a Y. As the tower rises into the sky, these wings circle the building, stopping at various heights to produce a series of ledges spiralling up the sides of the building. At each of these ledges, the tower has a different profile to the wind, which has the effect of deflecting and disrupting it – thus stopping the wind from forming organized currents that would cause the building to sway. And yet even with this impressive engineering, the top of the building still moves by a quease-inducing 2 metres

To see how all that high-level engineering performs, check out this video of a sandstorm hitting the tower, filmed from a head-cam at the very top of the building. And although it’s only a video, if you’re easily scared of heights, it’s probably best not to watch. (Seriously.)

Answer by Nathan Beal

Photo Credit: Sigma.DP2.Kiss.X3 via Compfight cc

Article by Nathan Beal

November 13, 2014

Nathan is currently in the throes of a PhD in Computational Chemistry at the University of Manchester. When he’s not behind a computer, he’s outside enjoying the sights of the city. A fan of The Walking Dead, he has a strange apathy to all things football-related.

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