The Economist has an interesting article on the technology and economics behind the recent skyscraper boom. Here are a few choice excerpts:
Skyscrapers are hard to build and even harder to make money from. Perhaps that is why they hold such an enduring fascination. “The problem of the tall office building”, wrote Louis Sullivan in 1896, “is one of the most stupendous, one of the most magnificent opportunities that the Lord of Nature in His beneficence has ever offered to the proud spirit of man.”
[Fans of "The Fountainhead" may know that Louis Sullivan's life was a "concrete inspiration" for the character of Henry Cameron, although Cameron is an independent character, not a fictionalized version of Sullivan. -- PSH]
Three sorts of changes have shaped the current wave of skyscraper design: materials, lifts and computing…
Translucent towers, which aside from looking pretty also alleviate one of the worst things about skyscrapers–the long shadows they cast on the streets below–are now proposed by architects everywhere. Thin-film technology (coating the glass in glazes that repel heat, but let in light) and self-cleaning glass are becoming standard. And glass can be formed into shapes that now make Mies’s conceptual design look rather conservative, as at 30 St Mary Axe in London (better known as the “gherkin”) or the Hearst building in New York.
Other changes to materials have helped towers weigh less, which allows them to go higher. Floors and walls have become thinner, thanks to innovations like slim-line insulation made of fibreglass and aluminium foil, an idea borrowed from containers used to transport blood. This brings its own problems, though. When a floor is really large, thin ones become like trampolines and engineers have to find ways to prevent the journey to the photocopier from becoming too bouncy.
Architects are also grappling with Mies’s other idea: dispensing with the central core, or breaking it up. Skyscrapers up to 200 metres tall can stand up with a central core of steel and concrete that houses a building’s lifts and the plumbing for support services. Any taller and the building needs outriggers, which provide support like the flying buttresses on a gothic cathedral. This structure can apparently be extended heavenwards indefinitely. The Burj Dubai is made up of a central core with outriggers. [See above image for an example of these "outriggers". -- PSH] It is determined to claim the title of tallest building in the world–so determined, in fact, that its final height is a secret and subject to elongation to keep ahead of would-be usurpers.
The second issue is elevators (or as the British call them, “lifts”).
But engineers also have to work out how to get people to the top floors.
Tall buildings have always relied on changes to lifting technology to go higher–the first hydraulic lifts around 1870 made it possible to go higher than the steam-powered lifts they replaced. Now, however, the constraints come less from the ability of a lift to travel half a kilometre vertically than from how long people must wait in the lobby for a lift to take them to the 50th floor. That makes it necessary to find ways to speed up their journeys around the building.
Most tall towers now have at least two banks of lifts: one for the lower floors and one for the upper ones. In the tallest towers in Asia (home to eight of the world’s ten highest giants) this still means waiting too long. So engineers run two or more lifts in each lift shaft, and build “sky lobbies” where passengers cross between lifts if they want to go the whole way down or up.
These arrangements, whereby cappuccino-carrying office workers or hotel porters are directed to a particular lift according to where they want to go, are collectively known as “hall call”. KONE, a Finnish lift company, is working on a lift system that sends text messages to people’s mobile phones as they enter a building, informing them to take lift five, say, if they want to go to their desk or lift seven if they want the cafe on the 60th floor.
And finally, advances in computing,
Contemplating buildings this complicated has been possible in recent years only because computers have became powerful enough to build three-dimensional models that developers, architects, structural engineers, mechanical engineers and builders can all work on. Before such computer systems arrived, design changes had to be made on several sets of drawings, which increased the chances of mistakes. Strange shapes constructed at lower levels were possible before computers sped up. But ambitious forms like the new 230-metre China Central Television building in Beijing (which looks a little like a bent croquet hoop) needed computer processors to design.
Computers have made other things possible, too. Engineers can use them to test how a building might stand up to a fire or an aeroplane crash. When the main tower at Canary Wharf was proposed in the 1980s, according to Peter Bressington of Arup, an engineering firm that is a prolific builder of skyscrapers, nobody was able to predict accurately how long it would take to evacuate if a fire broke out. Now Arup can run a simulation in which a fire starts on the 35th floor, one lift is out of action and a few thousand people have to get out, and see how long it takes.
As well as allowing skyscrapers to go taller, these changes have made them more efficient machines for living or working in and brought their running costs down.