This is a hole on top of the Shanghai World Financial Center.
This is a 660-ton steel ball hanging inside of Taipei 101.
And these are massive clockwise balconies on the Burj Khalifa, the tallest building
ever made.
These design choices might seem like gimmicks to give these skyscrapers their iconic looks.
But behind each feature is a brilliant engineering trick designed to one thing:
Confuse the wind.
Wind can cause a bunch of issues for buildings: broken windows, structural damage, and discomfort
for the people inside.
And today’s super-skinny skyscrapers have to deal with a particular wind-induced phenomenon
called vortex shedding.
This happens when wind flowing past a building creates vortices, strong swirls of air
that magnify the damaging effects of wind.
In low winds, these vortices cancel each other out.
But in higher winds, they create alternating low pressure zones that make the building
rock back and forth.
As the wind speed increases, so does the intensity of the back and forth movement.
Every object also has its own natural sway frequency
and when that matches with the frequency of vortex shedding, it creates a dramatic
spike in the intensity of swaying.
On the top floors of a high rise, that kind of swaying can be nauseating, plus it can
damage the integrity of the building.
But architects have an arsenal of tricks to reduce movement.
The first one?
Tapering.
The higher up you build, the stronger the wind force gets.
So to reduce surface area where the wind is stronger, designers can simply make a building
skinnier as it gets taller.
They can do that with tapering — like The Shard in London
or with periodic setbacks, like the Willis Tower in Chicago.
Then, designers can soften edges.
Hard edges aren’t good on wind, so you’ll often see skyscrapers with round corners.
But architects can achieve a similar effect with small cutouts from the edges.
Take Taipei 101, for example.
The building was originally designed with square corners,
but when a scale model was tested in a wind tunnel, the designers saw a lot of swaying.
Here are the results after designers added sawtooth corners.
They reduced movement by 25 percent.
The next option is pretty simple. You can just open it up with holes.
Skyscrapers like Saudi Arabia’s Kingdom Centre and Shanghai’s World Financial Center
do this with a single gap up top, allowing wind to pass right through where it’s blowing
the strongest.
But 432 Park Avenue in New York achieves this effect with several double-floor cutouts that
allow wind to pass through along the length of the entire tower.
There’s also twisting.
This wind resistance technique makes for some of the most stunning skylines today.
Dramatic spirals redirect the wind, guiding it upward and off of the building.
That’s the same wind resistance trick used by some industrial chimneys and car antennas.
Corkscrew shapes like this were impossible to build until fairly recently, thanks to
advancements in software and material science.
And they’re also promising from a sustainability perspective.
During the design process on the Shanghai Tower, for example, adding the iconic twist
reduced the wind load by 24 percent, saving developers $58 million in structural material.
Finally, there’s the technique so good it’s invisible: damping.
Dampers are mechanisms designed to absorb the energy from a building’s movement, counteracting
the effect of the wind.
Skyscrapers do this in two major ways.
First are slosh tanks: these are containers filled with several tons of water.
The water sloshes back and forth, and its weight displacement helps keep the building
from swaying.
Second are tuned mass dampers: massive weights suspended in the middle of a building.
These were traditionally hidden away in building design, placed on empty floors along with
other technical equipment.
But they don't have to be. Taipei 101's tuned mass damper has been a popular tourist
attraction since it opened in 2004.
They even have a mascot for it: Damper Baby.
It’s a little weird.
These shapes, holes, and counterweights form a secret design language hidden inside of
our skylines.
And as more people move out of rural areas and into urban ones,
skyscrapers will keep getting taller and skinnier.
These technologies are what’s making that future possible
and letting us keep building into the sky.
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