Two Kilometer Skyscrapers

Depending on the opinion you go with below, we may or may not be capable of building a 2km skyscraper today.   The materials science is there or roughly so, but there's a problem with elevators . . . as noted in the article, part of which is quoted below, a 1.4km building on the drawing board is considered iffy simply because of the enormous wasted volume of its numerous elevators.
  Kim believes that, technically speaking, a 2km might be possible at the current time. He continues: “At this point in time we can build a tower that is 1km, maybe 2km. Any higher than that and we will have to do a lot of homework.” 
Yet Kim states that it is highly impractical to build a 2km-high tower. He adds: “In terms of practicalities, we don’t need to built at 2km, but someone with a lot of money might still want to do it.” 
He points out that building at such height will incur many structural challenges. 
“There might be constraints for the structural engineering – we don’t know many things. When you go up to one or two kilometres, we don’t have much information surrounding the conditions.” Kim also notes that there may be issues with floor lean due to the shortening of columns over time. 
For WSP’s Leclercq, the technical limit at the current time is 1 mile. “I truly believe that 1 mile – 1.6 kilometres – is within range. Over that, it may be possible if there are improvements in concrete quality. But 2km is too big a figure – it’s just a step too far at the moment,” says Leclercq. 
DSA’s Kelshaw is similarly cynical on the feasibility of a 2km tower. “I don’t know why people would want to build something 2km tall. From a developer’s perspective that can’t be feasible. Just to think about that is mind blowing and I can’t see it happening in my lifetime.”
Compare this to Coruscant, where multikilometer skyscrapers have clearly been honed to a fine art.  I can't immediately think of any that are just so tall as to be off-the-chart orbital-tether tall, and I would presume five kilometers to be the rough limit just based on eyeballing the assorted scenes.  That, of course, doesn't account for the subsurface constructions, either, though it is not clear if there's much subsurface stuff underneath the skyscrapers themselves.

In any case, the other elevator problem is speed.  Better elevator cables could be a nice offshoot of orbital tether technology and other nanotech material designs.  Even if superfast elevators were feasible, though . . . say, via pressurized tubes that moved the cars or just nanotech cables or any other idea . . . there would still be a limit to the acceleration.   In an elevator in which you stand, which is generally the most efficient design volumetrically, you can hardly have a 90lb weakling expected to withstand 3g, not to mention the weightlessness or negative-g of a rapid descent.

I suppose we could consider reclining or even prone elevators where you sit in a G-seat or just lie down, but that comes with its own problems, like loading speed.  It's one thing to just walk in to an elevator and pack in like sardines, but quite another have a proverbial first-class section . . . the speed versus the added area (and with it, shaft volume) would require significant consideration.  And all of these things contribute to safety concerns in the event a rapid building evacuation is required.

I would say, then, that gravity control . . . altering the perceived g-forces within the elevator . . . is a likely prerequisite for good skyscraper design on Coruscant, so you can have comparatively few but ridiculously quick elevators that don't leave the building occupants as chunky salsa on the elevator floor.  Otherwise, the dozens upon dozens of elevators shafts as required by current skyscraper techniques would render Coruscant skyscrapers completely wasteful, not to mention the "last mile" problem of reaching a building quickly only to have to spend an age to get to the top.

Perhaps also, like Coruscant, the next true enabler for supertall structures is the flying car, so that when you arrive at the building's address, you're already on the 100th floor.

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