At the figurative and literal core of most buildings is a passenger lift, as the shaft is often constructed to exacting standards whilst the rest of the building is being built around it.
Because of this, the capabilities of lift design are a fundamental factor when it comes to designing and building huge skyscrapers such as the Burj Khalifa, a building that was only made possible thanks to the development of high-speed lift technology.
However, whilst lift speed and maintaining a comfortable atmosphere when travelling up to ten metres per second is important, the limiting factor in constructing buildings taller than this is far more fundamental and thus more difficult to address.
The pulley cabling, often known simply as the hoist ropes or rope for short, is the foundational component that makes lifts work.
Typically made from various composite materials such as steel or carbon fibre, rope connects all the way up a lift shaft and, in most conventional designs, is fundamental for it to operate. If the rope snaps, the lift does not move, although safety brakes will also ensure it does not fall.
Material engineers who specialise in skyscraper design will posit that buildings could theoretically be constructed significantly higher than even the Burj Khalifa, with mile-high buildings potentially possible with current construction techniques.
However, the limits to the rope are a fundamental limiting factor, and not just because of the height of the lift shaft itself.
Whilst conventional ropes limit the distance a lift can travel to around 500 metres, having multiple lift sections and changing points is a common part of skyscraper construction and would not theoretically stop a skyscraper from simply daisy-chaining as many lift shafts as is needed to connect the ground floor to the roof.
However, as a building gets taller, the more materials are affected by environmental and atmospheric conditions, a situation known as building sway.
This movement affects everything in the building, including the rope, which means that more advanced materials are needed to create increasingly tall skyscrapers, to say nothing of hypothetical space elevators.