PHYSICS IN DUBAI
BY SAMEER AND ARJUN
THE FASTEST ROLLER COSTAR
DUBAI METRO AND TRAM
Wind and earthquake safety
By a long shot, Earth’s tallest man-made structure is the Burj Khalifa in Dubai, climbing 2,717 feet (828 meters) into the sky. It’s 745 feet higher than the next tallest, the Makkah Royal Clock Tower Hotel in Saudi Arabia. Building the Burj required a whole new architectural design, called the buttressed core. It’s shaped like a tripod, with three main legs anchored to a central core that's responsible for most of the height. Rather than relying on super-strong steel and concrete mixtures, its very design gives it stability — each wing buttresses the other two.
Even with these architectural features, at some point, the amount of steel needed to stabilize higher floors becomes too heavy, forcing the building to become thinner. But this also protects it against wind. The Burj rises in a jagged pattern, with uneven levels topping out at varying heights around the structure to deflect gusts and prevent air vortices.
Moving people is probably the biggest challenge in the construction of supertalls. The most advanced elevators available, installed in the Burj Khalifa, can only climb 504 meters, so people have to get off and board secondary elevators to continue their journey to the top. Speed is another problem — the fastest elevator in the world, inside Tapei 101 Tower in Taiwan, rockets upward at roughly 38 MPH. Elevators can only descend at two-thirds that speed. Those limits are for us, not the technology: any faster and most passengers’ ears couldn’t withstand the pressure changes. So, for a building a mile high, you can expect very long rides and lots of transfers.
The higher the building, the wider the base that’s you need, so at a certain size simply getting across the ground floor poses another challenge. Commuting to work would take on a whole new meaning if you have to use a subway to get to the building, and then another subway or transportation system to move around inside it. It might make more sense to plan mega-talls as self-enclosed vertical cities, with work spaces, living spaces, grocery stores, entertainment, and other amenities together, said Werner Sobek, of Werner Sobek Engineers. “If this would be the case, if it was a vertical city, then I think the only limiting factor is transportation,” he said.
Architects could also get creative and employ Eiffel Tower-style designs with hollow bases. Buildings could be built to crouch above other, smaller structures — otherwise, the supertalls would also be superwide and probably too big to fill up.
What is height, anyway?
Like One World Trade Center, many of the world’s tallest buildings are actually shorter than they look, with the uppermost accessible floor lying some distance (and often a considerable distance) below the tip of the spire. This phenomenon, which the CTBUH calls “vanity height,” has increased roughly 400 percent since the mid-1970s.
Without vanity height, 44 (that's 61 percent) of the world’s 72 supertall buildings would measure less than 300 meters, losing their supertall status, according to the CTBUH. The tallest of these is the 390-meter CITIC Plaza in Guangzhou, China.
Buildings that reach a kilometer or higher, including the planned Kingdom Tower in Jeddah, Saudi Arabia, will likely meet that height with similar architectural features. But it’s certainly possible to go a mile up, maybe even higher than a mountain, some architects argue. At that point, the challenge becomes keeping people alive and healthy and comfortable, and designing buildings to compensate for lower atmospheric pressure and less oxygen.
Theoretically, Sauerbruch said, there’s no limit. “Whether this makes sense or not is another question,” he said.