Chicago, IL – Skyscrapers were the invention of New York City, and the Empire State Building held the title of “world’s tallest building” for 87 years. However, cities across the country around the globe have since been testing the limits to see just how high they can go.
An organization known as the Council on Tall Buildings and Urban Habitat (CTBUH) has defined the “supertall category” of skyscrapers as any building taller than 984 feet. To be categorized as “megatall,” the building must reach 2,600 feet in height. The height of a building is measured from the sidewalk to the structural top, including spires, but not antennas or flag poles.
For reference, the Empire State Building is 1,250 feet tall, the Willis (Sears) Tower is 1,451 feet tall, and the Burj Khalifa in Dubai is 2,716 feet tall. The Chinese broke ground on Changsha’s Sky City, which is expected to stand about 2,750 feet tall by mid-2014. At this time, there are 73 supertall buildings and 2 megatall buildings on Earth. From an architectural and engineering standpoint, several factors set these buildings apart from their less-impressive counterparts.
In the mid-1960s, an engineer, Fazlur Khan, introduced a structural system known as the “tube.”By replacing the internal steel frame of a traditional building with a series of inter-connected columns, Khan ensured that the strongest part of the building was on the outside. One a building exceeds 40 stories, wind becomes more of a concern than gravity.
But the tube design was abandoned in the late 1990s, as Bill Baker and Adrian Smith created a “stayed mast” design for Chicago’s 7 South Dearborn. This design featured a centered core, surrounded by eight large columns. Dozens of “post tube” designs emerged in the following years. However, Baker and Smith’s “buttress core” design, which involved a central hexagonal concrete core with triangular buttresses on three sides, secured Dubai’s Burj Khalifa as the tallest building in the world.
Today’s supertall buildings are unique in both design and composition. Although engineers once built high-rise buildings with steel, modern buildings contain a complex cocktail of chemicals and microfibers. Concrete is generally preferable to steel because a concrete tower can be thinner, without sacrificing wind resistance, and concrete towers don’t need fireproofing. Carbon-fiber materials, similar to those in jet airplanes and racing bikes, are promising but pose challenges of their own. Not only is carbon-fiber expensive, but its lightness and flexibility could feel insecure to people inside the building.
Although supertall buildings were once reserved for offices, they are being utilized for condos, hotels, restaurants, and shopping centers. Chicago’s Willis Tower is considered a single-function building because more than 85% of its total floor area is dedicated to office space. On the other hand, Chicago’s John Hancock Center is categorized as a mixed-use building because it has nearly equal parts office and residential space, with a large section for parking as well. Supertall buildings are trending towards mixed-use, especially as space becomes a rare commodity in overcrowded cities.
So aside from bragging rights, what do supertall buildings have to offer for the future? “Vanity height” is such a big deal that CTBUH recently produced a new report examining the egotistical side of skyscraper construction. Shockingly, the report found that 44 of the world’s 72 supertall buildings would lose their “supertall status” without their unusable, uninhabitable spires.
Statistical experts have predicted that the world’s population will surpass nine billion by 2050, and around 70% of these people will live in cities. Supertall buildings posit a solution to extreme urbanization growth, while regarding environmental concerns. For city-dwellers, they present the opportunity to go ice skating, see a movie, eat dinner, and get a night’s rest without ever taking a breath of fresh air. Despite terrorist attacks, anti-urbanization movements, and architectural challenges, supertall buildings have nowhere to go but up. Saudi Arabia’s 3,280-foot Kingdom Tower is set to open in 2017, but what’s next and how high will it go?