How tall can skyscrapers be? (with photos)

One consideration when planning skyscrapers is to wind guests atop buildings, such as the Burj Khalifa, which towers 2,717 feet above the ground.

For a long time, engineers and architects have speculated about how tall a skyscraper could theoretically be. Frank Lloyd Wright, considered the greatest American architect of all time, designed the 1-mile-tall (1.73 km) tower, The Illinois. This tower would be built in Chicago and would have 528 floors. It was designed in 1956 and probably could have been built back then, but at a great cost.

New York City’s Empire State Building has multiple rods to dissipate wind.

Structural materials are not the main factor limiting the height of the building. Very tall buildings are often surprisingly light for their size; after all, they are mostly empty spaces. Steel is strong enough to support structures 6.2 miles (10 km) or higher, while advanced composites can support buildings that reach 62 miles (100 km) or more.

The three main limitations on skyscraper height are wind, elevators, and budget.

A table of altitude vs. maximum wind speed looks like the following for a calm day in a temperate area:

Altitude Maximum wind speed 2 km (1.24 mi) 22 mph 4 km (2.28 mi) 56 mph 6 km (4.52 mi) 90 mph 8 km (4.97 mi) 134 mph 10 km (6. 21 mi) 179 mph 12 km (7.46 mi) 200 mph

Elevator restrictions force designers to limit the height of the building.

Above an altitude of about 12 km (7.45 mi), the wind calms down. It is also worth noting that the air becomes thinner with increasing altitude, slightly lessening the load from intense winds. On top of Mt. Everest, at just under 5.5 miles (~9 km altitude) high, the air is about four times thinner than at sea level.

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To counteract wind force on skyscrapers above about 500 feet (195 m) in height, special design features are required. This can include large internal counterweights, made of metal or even tubs of water, which shift to redistribute the weight towards the center of the building. Buildings composed of multiple stalks, such as the Empire State Building in New York and the Burj Khalifa in the United Arab Emirates, are also good at dissipating wind.

The Burj al Arab in Dubai.

Improvements in the load-bearing capacity of concrete have recently allowed the use of this rigid substance as a building material for very tall buildings, offering wind-dampening luxuries unavailable only with steel. The Ryugyong Hotel in North Korea, although never completed, would be an example of the use of concrete as a building material for this type of structure. Wind problems will certainly be challenging, but not insurmountable.

The Burj Khalifa is a skyscraper in Dubai with a height of 830 m, which makes it the tallest building in the world.

The lift factor is another major height limitation. The taller the building, the more people live and work in it, and the more ground floor space must be used for elevators. This challenge was met by two strategies: using double-deck elevators and using sky lobbies as waypoints for elevator travelers. Using overhead lobbies and local elevators for small sections of the building, a dozen or more elevators could share a single shaft, greatly improving efficiency. For very tall buildings over 6,500 feet (2 km) or more in size, multi-level elevators such as 5-story elevators may be required. Otherwise, the entire ground floor is dominated by elevators.

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The last major limitation on skyscraper size is, of course, budget. Burj Khalifa, the tallest building in the world currently with a height of 2,717 feet (828 m), cost an estimated $4 billion US Dollars (USD). Assuming that costs scale linearly with increasing height (a generous assumption), building a structure 6,500 feet (2 km) tall could cost $10 billion dollars. This is probably close to the limits of what developers would be willing to spend on a single project, though only time will tell.

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