Superstructures
Discover the engineering tech behind humankind’s biggest buildings as we track the rise and rise of the skyscraper
How clever engineering and technology have seen the rise of the world’s biggest skyscrapers
Today these Goliaths are often seen as symbols of national and civic pride, as well as being a key solution to urban overcrowding. Yet the skyscraper as we know it only came into being in the late-19th century, not through the ambition of architects but through a combination of contemporary engineering techniques and materials that finally triumphed over the builder’s age-old enemy: gravity.
For most of history the tallest human-made structure on Earth was the Great Pyramid of Giza at 147 metres – a height that would barely qualify as a skyscraper today. The reason was simple. Because all buildings were constructed from bricks and mortar, they were all built to the same principle: the higher the building, the bigger the base. However, all that changed with the Industrial Revolution and the ability to construct ever stronger and longer iron and steel girders. Suddenly buildings could be taller without having to take up so much space at ground level, sparking an international race that culminated in today’s tallest and most talkedabout buildings.
Skyscrapers are a monumental challenge to both design and construction. Winds can cause them to sway, earthquakes can shake even the strongest foundations and fires can melt through steel cores. As skyscrapers begin to approach the edges of thinner, colder air, living conditions must be adapted to compensate. For all these reasons, building skyscrapers remains a constant test of human ingenuity against natural forces.
Designing a skyscraper requires the combined efforts of hundreds of skilled professionals and thousands more to construct, usually to strict deadlines. It starts with planning, these days involving lengthy computer-aided design processes that must factor in everything from ground conditions and load and stress testing, health and safety guidelines and emergency evacuation procedures.
Once construction begins, attention focuses around a steel skeleton called the superstructure – a collection of vertical columns and horizontal girders that run through the building. This concentrates the downward force of gravity into a relatively small area at the base, transferred through the substructure – a series of steel columns, plates and springs underpinned by reinforced concrete – that extends far underground. This allows the building’s concrete and glass exterior, or curtain wall, to reach higher by effectively only having to support its own weight. Ultimately, however, the whole structure rests on clay, making the foundation just as important as the visible structure that rises above it into the clouds.
It is the superstructure that has to cope with the most strain. For the first skyscrapers – which rarely exceeded ten storeys – iron was used, but throughout the 20th century when the US ruled the world of high-rise construction, steel became the material of choice. Superstructures used to resemble a series of steel boxes containing both horizontal and vertical supports throughout to spread the load. However, as skyscrapers grew taller, the distance between these supports decreased, reducing available floor space – a vital consideration – as well as increasing weight. In the mid-1960s a new tubular design emerged based around interconnected exterior columns, reducing the number of interior columns required. It was this design that enabled the original World Trade Center and other record-beating structures to be made.
For nearly 150 years modern skyscrapers have been built to inspire shock and awe, relying on eye-catching designs and everhigher altitudes to attract tenants, businesses and visitors. In technical terms there is no real
reason why skyscrapers couldn’t reach three or even five kilometres, and with commercial airliners cruising above eight kilometres they’d have little to fear from accidental collision – although since 9/11 the public has understandably less confidence in such assurances.
Indeed, it is the threat of terrorism that poses the biggest obstacle to the continued dominance of the skyscraper. Ever since the twin towers of the World Trade Center in New York collapsed from the top down and inside out, architects have been forced to go back to the drawing board about how skyscrapers should be designed and the kind of events they should be built to withstand. Nowhere has this been felt more keenly than in the One World Trade Center, which opened on the Ground Zero site in
November 2014. Featuring not only a 56-metre windowless concrete base but also 0.9-metre reinforced concrete walls for stairwells and elevator shafts, windows made of blast-resistant plastic on one side of the building, dedicated stairwells for firefighters and a ventilation system including biological and chemical filters, safety and security now lie at the heart of this highly symbolic megastructure.
With the continuing risks involved in containing so many people in a single exposed building, as well as the escalating costs of building them, will future generations still idolise the skyscraper or is this just a new challenge to our 4,000-year obsession with
‘growing up’? Only time will tell…