The other mile-high club (skyscrapers)

[n2doc]

A new lightweight lift cable will let buildings soar ever upward
Jun 15th 2013

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.

Roped together
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.

more

http://www.economist.com/news/science-and-technology/21579437-new-lightweight-lift-cable-will-let-buildings-soar-ever-upward-other

[krispos42]

1. Or they could just mount electrified rails on the elevator shaft...

...and the drive motor on the car itself. Sort of like a subway train, only vertical.

The usual rails and safeties would hold the car in the shaft. Have rubber tires pressed against the walls of the shaft and driven by the motor.

Honestly, I had thought the really big buildings had moved beyond the steel-cable-with-counterweight design already.

[caraher]

2. This could use a lot more energy

The beauty of the counterweight system is that your motor (mostly) doesn't actually lift the load against gravity, it's there to accelerate the system and overcome friction (at least when in perfect balance). The "vertical subway" you envision would need a much larger motor than a comparable horizontal system because it has to lift the entire weight of the car (including the motor) against gravity.

I suppose one could devise a way to recover some of the energy when the elevator goes down. But the counterweight-based design is still popular because it's elegant and energy-efficient.

[krispos42]

3. That is very true

But my thinking is that because really talk buildings are something of an anomaly, and very expensive, the system had already been abandoned for today buildings. The extra energy used, compared to the other, regular buildings, would be minor.

The vast majority of elevators should be the counterweight kind, of course. If all elevators were like vertical trains we'd be wasting tons of power.

[WovenGems]

4. Oops!

Isn't this supposed to be a thread for bragging?