[Intro]
For nearly forty years, New York City’s Empire State Building was the tallest building
in the world.
Topping out at 381 meters, it now feels like something of a relic.
The tallest building currently under construction -- Saudi Arabia’s Kingdom Tower -- will,
if all goes as planned, be more than 2 and a half times taller than the Empire State.
Yes, we’re talking about a one-kilometer-tall building.
How is that possible?
And, how high can we go?
The short answer to the second question is: No one really knows.
But a good look at the Kingdom Tower and other super-skyscrapers will give you a sense of
the challenges that come with building something that’s as tall as, like, from here to the
nearest Starbucks.
Kingdom Tower was originally conceived as a mile-high building, or 1.6 kilometers, but
the project was scaled back after soil testing revealed layers of weak, porous limestone
and sandstone underneath.
To provide a sturdy foundation for this ginormous structure, 270 long concrete cylinders called
piles have been installed, as much as 1.8 meters in diameter and at depths up to 110
meters.
Working up from there, you have building materials to consider.
Three decades ago, the tallest buildings on Earth were mostly made of steel.
But steel is crazy heavy, so today’s super-structures are built mainly with concrete, or a combination
of steel and concrete.
Now, transporting concrete 800 meters above the ground requires some creative engineering,
and it may be one of the trickiest limitations to get past if we’re gonna go beyond the
1-kilometer mark.
For example, to construct the 828-meter Burj Khalifa in Dubai -- currently the world’s
tallest building -- engineers had to invent a 15-centimeter-wide pressurized tube to transport
wet concrete to the top.
And they had to do it all at night, so that in the heat of the day, it wouldn’t dry
en route to the 163rd floor.
Some engineers say the future of building materials may be in carbon-fiber composites,
the lightweight and super-strong materials that are already used to build fancy bicycles
and modern airplanes.
The downside is the cost: Carbon fiber is very expensive.
And, even if a builder could afford enough of it to get to one kilometer in height, there’s
still the question of how you keep the building standing.
Because the taller a building gets, the harder it is to stabilize.
Wind in particular is a constant challenge for building designers, and it’s more complicated
than just making sure the foundation is strong.
The tallest skyscrapers today have to regularly withstand wind speeds over 150 kilometers
per hour.
To do that, most are built with joints at the corners where steel beams can expand and
contract, allowing the building to sway.
That’s a good start.
But you also have to contend with wind vortices.
As the vortices keep moving, they quickly separate from the building, and when they
do, each one essentially pulls the structure toward it: These eddies of air end up yanking
the building from side to side, perpendicular to the flow of the wind.
This is called vortex shedding, and you might have seen its weird-looking effect on a flagpole
or light post on a windy day.
Wind-tunnel tests have helped engineers find some solutions to the phenomenon, like rounded
edges and notches on a building’s face that can act like wind-shock-absorbers.
But then, more practically, just about every skyscraper architect will tell you about the
elevator problem.
I mean, you can build the world’s tallest building, but if you can’t get people up
there to buy t-shirts, then … what’s the point?
So, the elevator problem is two-fold: First, elevator shafts can’t exceed 600 meters
in length -- at that point, the cables used to move the cars just become too heavy to
work.
In the Burj Khalifa, engineers solved this problem by creating what they call sky lobbies,
where passengers heading to the top get off, and take a second elevator ride.
But modern super-scrapers are also limited by elevator speeds.
No one wants to take 15 minutes to get to work on the 120th floor.
But if you go too fast, then you’re talking about air pressure and ear popping, not to
mention queasy passengers.
So most elevators don’t exceed speeds of 10 meters a second, and those have air pressure
controls and roller guides to dampen the vibrations.
To move people more quickly, one option may be electromagnetically-driven elevator cars
that don’t need any cables.
One company has already created a prototype using technology similar to the maglev motors
on new train systems.
So, it’s going to be 2019 at the earliest when the world gets its first look at a kilometer-tall
building, and we can learn how engineers defeated some, or hopefully all, of these problems.
Will we go higher?
Probably.
But until someone comes up with super cheap carbon fiber and perfects the electromagnetic
elevator, the steps are going to be incremental, and few and far between.
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