A new lightweight lift cable will let buildings soar ever upward
WHEN Elisha Otis stood on a platform at the 1854 World Fair in New York and ordered an axeman to cut the rope used to hoist him aloft, he changed cityscapes for ever. To the amazement of the crowd his new safety lift dropped only a few inches before being held by an automatic braking system. This gave people the confidence to use what Americans insist on calling elevators. That confidence allowed buildings to rise higher and higher.
They could soon go higher still, as a result of another breakthrough in lift technology. This week Kone, a Finnish liftmaker, announced that after a decade of development at its laboratory in Lohja, which sits above a 333-metre-deep mineshaft which the firm uses as a test bed, it has devised a system that should be able to raise an elevator a kilometre (3,300 feet) or more. This is twice as far as the things can go at present. Since the effectiveness of lifts is one of the main constraints on the height of buildings, Kone’s technology—which replaces the steel cables from which lift cars are currently suspended with ones made of carbon fibres—could result in buildings truly worthy of the name “skyscraper”.
The problem with steel cables (or “ropes” as they are known in the trade) is that they are heavy. Any given bit of rope has to pull up not only the car and the flexible travelling cables that take electricity and communications to it, but also all the rope beneath it. The job is made easier by counterweights. But even so in a lift 500 metres tall (the maximum effective height at the moment) steel ropes account for up to three-quarters of the moving mass of the machine. Shifting this mass takes energy, so taller lifts are more expensive to run. And adding to the mass, by making the ropes longer, would soon come uncomfortably close to the point where the steel would snap under the load. Kone says it is able to reduce the weight of lift ropes by around 90% with its carbon-fibre replacement, dubbed UltraRope.
Carbon fibres are both stronger and lighter than steel. In particular, they have great tensile strength, meaning they are hard to break when their ends are pulled. That strength comes from the chemical bonds between carbon atoms: the same sort that give strength to diamonds. Kone embeds tubes made of carbon fibres in epoxy, and covers the result in a tough coating to resist wear and tear.
According to Johannes de Jong, Kone’s head of technology for large projects, the steel ropes in a 400-metre-high lift weigh about 18,650kg. An UltraRope for such a lift would weigh 1,170kg. Altogether, the lift using the UltraRope would weigh 45% less than the one with the steel rope.
Besides reducing power consumption, lighter ropes make braking a car easier should something go wrong. Carbon-fibre ropes should also, according to Mr de Jong, cut maintenance bills, because they will last twice as long as steel ones. Moreover, carbon fibre resonates at a different frequency to other building materials, which means it sways less as skyscrapers move in high winds—which is what tall buildings are designed to do. At the moment a high wind can cause a building’s lifts to be shut down. Carbon-fibre ropes would mean that happened less often.
All of which is worthy and important. But what really excites architects and developers is the fact that carbon-fibre ropes will let buildings rise higher—a lot higher.
via The Economist
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