“By night the skyscraper looms in the smoke and the stars
and has a soul.” – Carl Sandburg
In 1956, architect Frank Lloyd Wright
proposed a mile-high skyscraper.
It was going to be the world’s tallest building,
by a lot — five times as high as the Eiffel Tower.
But many critics laughed at the architect,
arguing that people would have to wait hours for an elevator,
or worse, that the tower would collapse under its own weight.
Most engineers agreed,
and despite the publicity around the proposal,
the titanic tower was never built.
But today, bigger and bigger buildings are going up around the world.
Firms are even planning skyscrapers more than a kilometer tall,
like the Jeddah Tower in Saudi Arabia,
three times the size of the Eiffel Tower.
Very soon, Wright’s mile-high miracle may be a reality.
So what exactly was stopping us
from building these megastructures 70 years ago,
and how do we build something a mile high today?
In any construction project,
each story of the structure needs to be
able to support the stories on top of it.
The higher we build,
the higher the gravitational pressure from the upper stories on the lower ones.
This principle has long dictated the shape of our buildings,
leading ancient architects to favor pyramids
with wide foundations that support lighter upper levels.
But this solution doesn’t quite translate to a city skyline–
a pyramid that tall would be roughly one-and-a-half miles wide,
tough to squeeze into a city center.
Fortunately, strong materials like concrete
can avoid this impractical shape.
And modern concrete blends are reinforced with steel-fibers for strength
and water-reducing polymers to prevent cracking.
The concrete in the world’s tallest tower, Dubai’s Burj Khalifa,
can withstand about 8,000 tons of pressure per square meter–
the weight of over 1,200 African elephants!
Of course, even if a building supports itself,
it still needs support from the ground.
Without a foundation, buildings this heavy
would sink, fall, or lean over.
To prevent the roughly half a million ton tower from sinking,
192 concrete and steel supports called piles
were buried over 50 meters deep.
The friction between the piles and the ground
keeps this sizable structure standing.
Besides defeating gravity, which pushes the building down,
a skyscraper also needs to overcome the blowing wind, which pushes from the side.
On average days,
wind can exert up to 17 pounds of force
per square meter on a high-rise building–
as heavy as a gust of bowling balls.
Designing structures to be aerodynamic,
like China’s sleek Shanghai Tower,
can reduce that force by up to a quarter.
And wind-bearing frames inside or outside the building
can absorb the remaining wind force,
such as in Seoul’s Lotte Tower.
But even after all these measures,
you could still find yourself swaying back and forth
more than a meter on top floors during a hurricane.
To prevent the wind from rocking tower tops,
many skyscrapers employ a counterweight weighing hundreds of tons
called a “tuned mass damper.”
The Taipei 101, for instance,
has suspended a giant metal orb above the 87th floor.
When wind moves the building, this orb sways into action,
absorbing the building’s kinetic energy.
As its movements trail the tower’s,
hydraulic cylinders between the ball and the building
convert that kinetic energy into heat,
and stabilize the swaying structure.
With all these technologies in place,
our mega-structures can stay standing and stable.
But quickly traveling through buildings this large is a challenge in itself.
In Wright’s age,
the fastest elevators moved a mere 22 kilometers per hour.
Thankfully, today’s elevators are much faster,
traveling over 70 km per hour
with future cabins potentially using frictionless magnetic rails
for even higher speeds.
And traffic management algorithms group riders by destination
to get passengers and empty cabins where they need to be.
Skyscrapers have come a long way
since Wright proposed his mile-high tower.
What were once considered impossible ideas
have become architectural opportunities.
Today it may just be a matter of time
until one building goes the extra mile.
How do engineers ensure that these massive structures
don’t come down in a massive earthquake?
Check out this lesson,
and learn why it’s not the sturdiest buildings,
but the smartest, that remain standing.