With the rapid growth of countries like China and the unparalleled success of Dubai as the tax-free haven of the Middle East, a new type of building has emerged over the last decade: the supertall tower.
The term, implemented by many professional periodicals and the Council on Tall Buildings and Urban Habitat, is little more than a fashionable one, separating skyscrapers in two categories: those that are between 100 to 300 meters (980 ft) from the less than 60 buildings that defy gravity and reach heights in excess of 300 meters.
Unlike The Home Insurance Building in Chicago (long since demolished), considered by many as the first skyscraper ever built, the advent of the supertall towers is the product of economic prosperity and not of technological breakthroughs. This is why The Burj Khalifa (originally Burj Dubai), the current world’s tallest, utilized the same structural concept employed at a much smaller scale in the Sears Tower (now Willis Tower) over 30 years ago.
Though they reach for the skies, these supertall buildings are often bound to earthly structural configurations that lack the inventiveness of older tall predecessors. An illustrative example is precisely the Burj Khalifa, a colossus of concrete, steel and glass sitting in the desert of Dubai, defying the inclement weather, which includes the occasional sandstorm. The tower was designed to be the tallest and also the costliest, with luxurious interiors pitched to those with deep pockets. The structural strategy that allowed it to rise to the incredible height of 829 meters (2,722 ft) is referred to as “the bundled tube concept“. The idea is to group a series of steel-framed cages with columns at the perimeter in order to gain stiffness and sustain great lateral loads (wind). This is the case of a system where the whole performs better than the sum of its parts. It might be easier to think of the concept as a stack of cards you are trying to rip. The more cards you hold, the harder it is to rip them.
These supertall towers often limit their aesthetic impact to an uninterrupted glass skin that represents the continuation of the modernist idealist glass boxes that began to populate cities over 50 years ago. The problem here does not lie on the implementation of an old idea, but on the use of concepts that do not reflect the current global circumstances. It bears to remember that modernist boxes came about in a world that was not nearly as worried about energy consumption and environmental change. Experience has long since suggested that these modern pieces are heat sinks when temperatures rise and glassy icy boxes that shed heat when temperatures drop.
To justify construction at a performance level, what often happens is that designers resort to energy-saving strategies that put a higher price tag in return for greater efficiency. How does the Burj Khalifa, for instance, justify its continuous glass skin in a desert-like habitat? The answer is by adding layers of glazing, reflective glass tints and insulating coats that are usually sprayed or injected into the air chambers sandwiched in between thin glass panes. To me, these tactics are a way of cheating, allowing designers to insist on materials and design schemes that are not naturally suitable to the context they are in.
However, it would be naive to suggest that these glass facades are not what people want, both aesthetically and functionally. After all, how successful would a designer really be if he/she were to insist on alternative building skins that are simply not as visually appealing as glass? Performance still does not sell as well as beauty.
There are a few instances in which passive techniques and other site-specific measures have driven the design of skyscrapers. There is, for instance, the SOM-designed National Commercial Bank in Jeddah, Saudi Arabia. Due to average high temperatures that are enough to superheat a glass structure, the building turns its back to the city around it. The offices and glass skin are disposed towards the center, facing a huge atrium carved out in the middle of the triangular plan. This scheme is not only effective in providing shelter from high outdoor temperatures, but it is a unique aesthetic statement that separates the high-rise from the rest, looking like a monolithic piece of stone shaped by the desert, rather than the glassy boxes that bear no relation to their context.
It is ironic that in the exclusive club of the supertall, architects and clients have opted for such conservative and traditional designs. Instead of the exoskeleton of giant steel X-braces that elegantly describe the John Hancock Center in Chicago as it tapers upward (completed in 1968), supertalls have simply taken the concrete tower of 20 to 40 stories and multiplied its size.
This is where Sky City, the soon-to-be tallest building ever in China, is a breath of fresh air. What it does differently is that it proposes a lightweight steel structure that does away with the heavy, time-consuming, energy and labor-intensive reinforced concrete core. In conjunction, the tower is to rely on prefabricated parts that will be shipped and connected on-site to the rest of the structure. The goal is to save time, employ less labor and simplify the process of construction. The lightweight and unconventional character of the structure will also set it apart on a purely visual level, allowing the glassy facade to be a lot more airy and lighter than it can usually be.
If it were to be approved and the structure passes rigorous feasibility analysis, Sky City is a step in the right direction in the development of supertall towers. This is a building that is informed by technological innovation and an original structural configuration that is driven to lower costs, simplify construction and reduce the impact of the massive project in the environment.
There is, of course, the question of whether supertall buildings are really necessary, especially when seen from an environmental perspective. The answer to this question is simply NO. Supertalls are terribly unnecessary and often respond to a client’s wish for exposure. The idea is that the taller the skyscraper is, the more interest the building will generate, and a higher premium can be charged for condominiums at great heights.