All language subtitles for How.Did.They.Build.That.S03E05.Heights.and.Balance.1080p.HULU.WEB-DL.AAC2.0.H264-WhiteHat_track3_[eng]

[Jay] How do you build

a 1.2 million-square-foot
office building

on a 45-foot-wide strip of land?

There's no room to put anything,
to even start construction.

The equipment is large
and the site was tiny.

[Jay] How do you
realize a wild idea

for a mind-bending building
perched on a parking garage?

[Laurie] One of the younger
architects said, "Hey, look!

This actually
looks like a pterodyactyl."

[music]

[Jay] And how do you
make a suspension bridge

312 feet in the air

across a half mile-wide
mountain valley?

These guys were working at the
height of the State of Liberty,

from the ground
to the torch in the air.

[music]

[Jay] This is the age
of the extraordinary.

[Dr. Agbedor]
It's totally different

from anything around it.

It's like a visitor
from another planet.

[Jay] Where ingenious
engineers have unleashed

unchecked creativity.

Now their secrets are revealed

as we discover the amazing
stories of their construction.

[Mat] Look at this building,

and your brain
just screams at you,

"This building
does not make sense!"

[Jay] To try and understand...

how did they build that?

If there's one way to guarantee

a truly breathtakingly
original building,

it's to ask an architect
to deliver the impossible.

Now, Chicago is a city with
more than its fair share of

incredible buildings.

So when a plot of land
came up that was too small

to build anything useful on,

it was time to turn
the idea of a skyscraper

completely
upside down--literally.

Chicago, Illinois is home
to around 2.7 million people.

It's the United States'
third-largest city,

and one of the most
densely populated.

With barely
any available land left,

developers here have been forced
to rethink the impossible.

But when they took on an
extra challenging plot of land

pinned in by
the river, the railroad,

and restrictive planning laws,

no one knew
if they would pull it off.

[Erik] There is nothing
there to work with.

You stare at it and realize,

how are we gonna put
a building there?

[Jay] By defying the laws
of gravity, that's how.

This is 150 North Riverside,

a huge office building
balanced precariously

on its tiny base.

[Dr. Agbedor] You can't
believe that tiny stem

is able to support
that weight on top of it.

[Jay] An extraordinary
feat of engineering,

constructed on a site
with one of the country's

busiest stretches of
railroad passing through it.

[Chris] The most important thing
was not building the building.

The most important
thing on the site

was keeping the trains running.

[Jay] It took almost six years
and $270 million to complete.

[music]

[Jay] So, how did they build it?

[music]

[Jay] In the 19th century,

the Chicago River
was a vital artery

for the booming lumber
and meatpacking industries.

But, as the railroad took over,

the city turned
its back on the water.

[Anthony] The river
had become kind of

a dumping ground
for trash and sewage.

And it wasn't 'til
the early 2000s

when Chicago really
began reinvesting into

beautifying the river
and amenitizing the river.

[Jay] By 2011,

much of the riverfront
has been revitalized,

apart from
one small strip of land.

This was the last
available riverfronting site,

um, that hadn't been developed.

This piece of property
was extremely valuable

from that standpoint,

if you could just
figure out how to do it.

[Jay] To make sure it pays off,

the developers want to create
1.2 million square feet

of office space.

The problem is the site
is incredibly narrow,

wedged in between the river
and the main railroad route

into Union Station.

What's more,
Chicago planning laws mandate

that all new buildings are set
back a minimum of 30 feet from

the water to provide
a walkway along the riverfront.

When you put the area where
you couldn't build anything,

we were left
with a strip of land

that was about 45 foot wide.

The 1.2 million-square-foot
office building

needs a footprint of
at least 28,000 square feet.

What they have is just 6300.

[Jay] To make the money work
and keep the city happy,

the architects
come up with a daring plan

that breaks all the normal rules
of skyscraper construction.

Usually tall buildings
have a big base

and get narrow as they go up.

They want to literally
turn that idea on its head.

To pull off this
astounding balancing act,

first, the team
will have to dig deep

into the Chicago
bedrock to anchor

a slim, but incredibly
strong concrete core

752 feet tall
and just 39 feet wide.

[music]

[Jay]
Then they'll need to engineer

a mighty steel support system
that will act as a tabletop,

holding the weight of
a 54-story office building

and channeling
its forces into the ground.

By lifting the offices up,

they will create space
for a riverside walkway

to the east.

But they want to take
things one step further--

enclosing the railroad tracks
to the west,

creating space
for a public park.

If they succeed,
the result will be

an astonishing Y-shaped building

that appears to teeter
over the waterfront.

Before they can even start,

there's a fairly big
problem to overcome--

getting the
materials, machinery,

and manpower needed
onto the site.

There's no room to put anything
to even start construction.

The equipment is large
and the site was tiny.

[Jay] It's impossible
to access by road,

boxed in by railroad tracks,
elevated bridges,

and the water.

So the team turns
that to their advantage.

[Chris] Ultimately
we took the approach

to view the Chicago River
as a liquid roadway

to bring equipment in

to remove excavated
soil from the site.

[Jay] Not only can
they use the river

to get materials
on and off site,

but it also offers
the chance to create

much-needed space to work.

The contractor put a large
90-foot barge on the river

and a ginormous crane.

[Chris]
Being able to utilize that

more than doubled the amount
of available space that we had

while still maintaining
all of the river traffic

and making sure that even the
largest Chicago river traffics

were able to pass by
all of our operations.

[Jay] In 2014,
with the barges in place,

construction begins.

The first challenge
is to create foundations

strong enough to support
the huge skyscraper

on its tiny base.

It takes six months
drilling 16 boreholes

into the bedrock...

...each 10 feet wide
and 120 feet deep

before filling them
with concrete and steel.

The plan is to
tie these together

by pouring a 10-foot-thick
concrete mat on top.

But it's now February,

and in Chicago, the average
low temperature is 20 degrees.

Cold slows down
the concrete curing,

which risks weakening.

And even if
a small area freezes,

it can cause serious damage.

So the team decides to
speed up the arrival of spring.

[Erik] They spent the few days
having to first preheat the hole

so that the concrete
wouldn't start to freeze up

as soon as it hit
the ground on contact.

[Jay] With the help of concrete
blankets and propane heaters,

they are finally ready.

This will be the second-biggest
pour in Chicago's history--

3600 cubic yards of concrete

which has to be
poured in one go.

[Dr. Agbedor] As soon
as the concrete is poured,

it starts to set.

And if another round of concrete
is poured on top of that,

not in a continuous manner,

you will introduce
lines of weakness

which will jeopardize
the structural integrity

of that concrete.

[Jay] How will they
pour all that concrete

without stopping?

[Jay] In Chicago,
the team trying to balance

a 1.2 million-square-foot
office building

on a base just 39 feet wide

is about to pour
the 3600-cubic-yard

concrete mat foundation.

It's a huge operation
months in the planning.

So when the day arrives,

on the evening of Friday,
February 13, 2015,

there's no going back,

even if that means working
through a blizzard.

Once we started pouring,
we couldn't stop

until we completed it.

[Jay] To keep the
concrete flowing,

they need two pumps

and 336 trucks
working around the clock.

There's no good way to bring

the concrete trucks
close to the hole,

so they're up on the bridges
with their long pumps and booms.

Uh, it was a very long process.

[Jay] Finally,
24 hours after they began

late on February 14th,
the job is done.

I'm sure all the, uh,
significant others at home

were not happy about them
sticking through that

on Valentine's Day,

but it was a good
Valentine's Day

for the project team, for sure.

[Jay] The next challenge
is to execute a bold plan

to transform the railroad
lines running through

the west side of the site
from an eyesore

into an oasis.

[Jay] The architects
wanna cover them

with a 100,000-pound
precast concrete deck

and create one and a half
acres of green space.

Supporting it all
will be 113 very thin,

very strong piles
set between the tracks.

[Chris] The micropiles
are basically

10 inch diameter pipes

drilled into the bedrock

about every five to seven feet.

[Jay] But this is a
busy commuter route

serving Chicago's Union Station.

Trains pass through
every five to seven minutes

from dawn to dusk.

And Amtrak stipulates
that the work must be done

without any disruption.

Our goal was that
no train passenger,

no train operator
knew what was going on.

[Jay]
So, how could they do that?

[Rob] The contractor
negotiated with Amtrak

the hours between
midnight and 5:00 AM

for operating in the tracks.

[Corina] This is like
Mission: Impossible.

Every night they have to
sneak into the railyard

and build against the clock.

[Erik] It was a rough couple
of months for the neighbors,

there's no way around that.

The contractor did
everything they could,

giving them good notices,

sending them over apology
donuts every now and then

after an especially rough night.

[Jay] After four
months of piling,

the team starts
laying the 107 pieces

of precast concrete.

Each one is 80 feet long
and weighs 75,000 pounds.

[music]

[Jay] Eventually, the area
will be transformed into a park,

but it also serves
an immediate purpose.

[Erik] Suddenly we had
a luxuriously sized

construction site

to bring in trucks and all
the materials and everything.

[music]

[Jay] It's now summer 2015,

and the team's attention turns
to building the skyscraper

and making sure
it's strong enough

despite the tiny base.

Usually a high-rise building
has columns around the edges,

which transfer the loads
directly into the foundations.

But here we don't have that.

Those columns are left
hanging in the air

eight floors from the ground.

[Jay] It falls to the
team to come up with

an elegant solution
to this major challenge.

We basically build
a truss system

that, uh, uh, angles
the forces into the core.

[Jay] A truss system
uses triangles,

known for their
strength and stability,

to distribute weight.

Here, 16 massive steel trusses

will funnel the forces
created by the tower

into the slender concrete core.

With 54 stories to handle,

they need to be
very, very tough.

No ordinary steel is
strong enough to cope.

[Rob]
There's a mill in Luxembourg

that produces the largest
roll shape in the world,

and it produces 65 ksi steel,

which is 20% stronger
than conventional steel.

It weighs 925 pounds
per lineal foot, so half a ton.

It's, uh, the biggest,
baddest shape in the world.

[Jay] As each
truss is assembled,

it must be perfectly
symmetrical.

Any mistake could throw off the
engineers' careful calculations.

[Rob] If you think
about a champagne flute

or a ballerina en pointe, right?

It's all about balance
on that very narrow base.

[Jay] By September 2015,

the truss is complete.

And 150 North Riverside
begins to climb rapidly

towards the sky.

[music]

[Jay] But the
700-foot-tall building

has one more challenge
for the engineers to overcome

in the Windy City.

[Rob] As the winds
blow in Chicago,

the building will naturally
move back and forth.

[Jay] To stop the
inhabitants getting seasick

or, in this case, windsick,

the engineers add a simple,
but ingenious extra feature

above the office accommodation.

It involves 160,000
gallons of water.

[Rob] We introduced
these damper tanks.

They're filled with water.

And as the building
wants to move this way,

the water pushes back
the other way, and vice versa.

And so it settles
the movement of the building.

[Jay] In February 2017,

30 months after work began,

150 North Riverside
is finally complete.

Over 1.2 million
square feet of office space

now stands proud beside
the Chicago River.

Its extraordinary engineering

is wrapped in 540,000
square feet of shimmering glass.

[Erik] The building
itself is beautiful.

When the sun comes up the
Chicago River from the south,

the whole façade
just blazes white,

and it's just
a glorious experience.

[Jay] Its astonishing shape
has earned it nicknames,

including the Champagne Flute
and the Tuning Fork.

Generally speaking, I think
it's a very clever design.

I think it's very aesthetic.

I don't know if there's an
architectural reasoning for it,

but it's very pretty.

[Woman] I feel like this
building defies gravity,

so the people behind
it must be geniuses.

I don't try to
figure it out too much.

I just enjoy it.

[Jay] Thanks to
the tiny footprint,

there's space
beneath the offices

for a landscape
riverside footpath on one side

and a peaceful park
on the other.

[music]

[Corina] It's a special
kind of building

that simultaneously creates

a new kind of
commercial development

and it also gives
back to the community.

[Jay] The untapped potential
of one of Chicago's

most challenging sites

has finally been unlocked.

[music]

[Chris] I lived it.
I breathed it.

I lived and died by
the failures and the successes.

150 North Riverside
represents everything

that I think that
I'm capable of professionally.

[music]

Los Angeles has long been
known as the City of Angels.

But with the arrival of

a jaw-dropping
new office building,

the City of Angles would
perhaps be more accurate.

And while it may be
named after a creature

from the dinosaur age, trust me,

the Pterodactyl Building
could not be more futuristic.

[music]

[Jay]
In Culver City, Los Angeles,

there's an extraordinary
new building in town.

Is it a bird?
Is it a parking garage?

[Jay] Part parking garage,
part office building,

part Jurassic bird.

Wait, what?

[Jay] This is what happened
when an inventive developer--

Nothing like it really
had ever been done before.

[Jay] --and a
trailblazing architect--

With a wall, with a floor,
with a roof, with a window.

[Jay] -- decided to turn
the dull and mundane

into something that would
stop you in your tracks.

I mean, you turn the corner
in this business district,

and you're like, "What is that?"

[Jay] This is the Pterodactyl.

So, how did they build it?

[music]

[music]

[Jay] Culver City, California

rose to fame as home
to some of Hollywood's

biggest movie studios.

In its mid-20th century heyday,

tucked among the movie lots were
small factories and warehouses,

producing everything
from props to wardrobe.

Fast forward to
the 1980s, though,

and many of those buildings
had fallen out of use,

including an area
called Hayden Tract,

where 60 acres of
warehouses now lie empty.

Developer Samitaur-Smith
spot an opportunity

to transform this area,

building workspaces for the
new start-up tech companies

springing up in LA.

[Dr. Mabry] Samitaur-Smith

aren't your typical
commercial developers, though.

This is a creative
power couple.

Before they turned to
property development,

Laurie Samitaur-Smith
acted in Hollywood,

while her husband once
worked for Pablo Picasso.

We had to do some dynamic,
different-looking

kinds of buildings.

We couldn't build blah,
boring, typical buildings

that you see on
every city street.

We had to do
something different.

[music]

[Jay] To help them
achieve their vision,

they joined forces
with Eric Owen Moss,

a local architect
unafraid of breaking the mold

with his ideas for what
a modern office can be.

It doesn't have to be elevators,
double-loaded corridors,

and nine-foot
floor to ceiling heights.

It can be all over the place.

He sees things in a building
that most architects don't.

[Jay] Together,
they begin gradually

transforming Hayden Tract

into an architectural
laboratory.

[Laurie] As we were successful

and got more and more tenants,

we were able to afford to
build more and more buildings.

And each time,
the building was an experiment.

[Jay] In the late 1990s,
though, they hit a roadblock.

City planning rules
mean that before

they can add any more
office space to the area,

they must first build parking
for at least 530 cars.

[Laurie] We had no ambition
to build a parking structure.

Still to this day they are
the epitome of ugliness.

[Jay] Laurie Samitaur-Smith
throws down the gauntlet

to Moss.

[Laurie] "I want you to
design something incredible

"that will grab the eye,

"so when they drive in
the driveway,

"they don't see the ugly four
levels of a parking structure.

They see something on the
roof which is unbelievable."

[Jay] Moss takes that
brief and begins designing.

His idea is to hide the parking
garage with an office building

that will look like
a haphazard collection of boxes

perched precariously
on its edge.

[Eric]
So having built the garage,

the building is hung over
the face of the building.

[Jay] Pulling this off, though,

will call for some serious
creative thinking.

[music]

[Jay] At the heart
of the new building

will be a brand-new garage

with parking for 800 cars

and the ramps to
connect the four levels

sitting at the front.

So far, so ordinary.

But the team will
have to find a way

to bury enough
structure in the garage

to support what's to come.

Then they'll need to design
and build a steel skeleton

strong enough to
support the weight

of the intricate
interconnecting boxes

and to prevent them
from tipping forward

as they're built over the edge.

Finally, the building
will need to be wrapped

in a material to protect it
from the California sun

while maximizing
the dramatic effect

of its bird-like form
swooping down

over the front of
the parking garage.

One of the younger architects
stood back one day

and looked what he was drawing.

And he said to
everyone around him,

"Hey, look!

This actually looks
like a pterodactyl!"

And the name stuck.

[music]

[Jay] In 1998, work begins.

The developers
don't yet have the funds

to build the Pterodactyl itself.

So they start with
the four-story parking garage.

The garage is very
straightforward, functional.

Garage floors and ramps.
It's pretty mundane.

[Jay] But there is
one way in which

this differs from
the run of the mill garage.

Eventually it will have
the extraordinary shape

of the Pterodactyl
hanging off of it.

So it's vital to build
sufficient support

into the structure now.

The answer lies in
18 vast steel columns.

The columns are
extended two levels

above the top deck,

so the top of the fourth floor,

and in anticipation
that the Pterodactyl itself

would be built at some point.

[Jay] It takes
more than ten years

to get the money together
for the main building.

But in June 2012,
Samitaur-Smith

finally receive the
email from the bank

they've been waiting for.

And I'm wearing that email.

Let me put my glasses on.

Our banker wrote the email,

"Order the steel!"

[music]

[Jay] They're ready
to start construction

and the team is facing
its first problem.

The nine office boxes
are designed to look like

they're sitting
effortlessly on the garage.

But at around 15 tons each,
they're gonna need supporting.

One of the main challenges

that kind of
is the core of this project

is the fact that we are
sitting on several columns,

and that's all
we have for support.

[Dr. Mabry] If this was a
standard rectangular building,

it would be relatively
straightforward

to funnel the loads
through the 18 columns

that are sticking out
of the parking garage.

But this building is
anything but standard.

[Jay] The building's
unique design

requires a unique solution.

[Hooman] We came up
with these frames

that provides
a support point for each box.

[Jay] It's an ingenious
piece of engineering.

First, the 18 steel columns
will be braced with beams.

Then a series of steel
rings will be created

to encircle the boxes.

These will carry the load
from the boxes into the beams,

then down through the columns
and into the parking garage.

Now they have to build it.

And that involves creating
10,000 individual pieces

of steel.

We knew we had to fabricate
the pieces offsite

because onsite
would've just been impossible

and not have the accuracy
we needed them to have.

[Jay] Then the team
has a mammoth job

of getting the right part
in the right place.

So we had to come up with apps

that kept track of
more than 10,000 members.

Not only are they building
a 10,000-piece jigsaw,

the tolerance of each piece
is just 1/8 of an inch.

The level of detail
we had to go through

was honestly incredible.

[Jay] Despite the challenges,

the Pterodactyl's
steel skeleton creeps forward.

Next, they have to suspend
the boxes over the edge.

Architect Moss has
designed them to look like

they're about to
crash into the ground.

The challenge is
making sure they don't.

One of the features
of the building was

that it was overhanging
from the edge of the garage,

and one of the
challenges with that is

there aren't any
supports within the ramp.

What this means is
that the force created

by hanging
the boxes off the side

has to be channeled back to
the steel columns on the roof.

[Jay] The team turns
to an engineering trick

called a cantilever,

used to create
the seemingly impossible.

A cantilever is an overhang
that's supported on one side.

There's different
ways it can work,

but the secret is to have
a piece of steel or a beam

that's hidden out of sight.

[music]

[Jay] The problem here
is that the design of the boxes

leaves nowhere to hide
a large piece of steel.

Not only do they need to look
sharp edged and delicate,

they need to merge
and interconnect

in complicated ways.

[Hooman] There was some
really tight areas,

so we didn't have room
for structure, per se.

And it still had to
hold up the building.

[music]

[Jay] So, how will they
pull off the impossible design?

[music]

[Jay] In Culver City,

the team needs to support
the vast weight of a building

that hangs perilously over
the edge of a parking garage

without compromising
its sleek, futuristic look.

The solution is to hide
strategically placed

smaller pieces of steel
all over the frame,

which work together to
hold up the cantilever.

[Hooman] We added
braces in certain areas

kind of like pulling up
on a hanging area

to strengthen it

so that it would perform
the way we needed it to perform.

In some areas,
we didn't have room for braces,

so we had to put two members
next to each other,

kind of doubling up the members.

[Jay] It takes almost two years
and 134 tons of steel.

But finally, the complex
overhanging frame is complete.

[music]

[Jay] The final challenge
is to clad the exterior

in something that will
weatherproof the building,

while also creating
a final finish worthy

of Laurie's singular vision.

[Laurie] I always
had this fantasy that

one day that pterodactyl

was just gonna
start to flap its wings

and take off,

and just fly across
the pavement, you know,

from the parking structure
to my window, to me.

[music]

[Jay] Fitting, then,

that the team decides to cover
this prehistoric fantasy

of a building in scales.

Well, okay, tiles.

About 28,000 square feet
of them made from zinc.

[Corina] The zinc tiles
are a really clever solution.

They're weatherproof.

They won't rust.

And they're flexible
enough to wrap around

the corners of the building,

essentially hide
in the building's recesses.

But actually, most of all,
they look amazing.

[Jay] In 2015, 17 years
after it was first designed,

the Pterodactyl
is ready for action.

It couldn't be more at home
than in Tinsel Town.

It looks like a huge
blockbuster special effect.

[Jay] Its gleaming angles
and gravity defy form,

show what happens
when daring designers

push engineers to their limits.

[Hooman] This project
was very special.

I am very lucky to
have the opportunity

to solve this puzzle.

[Laurie] I'm not saying that
it's everybody's cup of tea.

But there are enough
people out there

who say, "That's what I like.
It's something different."

That was, and is,
the Pterodactyl.

[music]

[music]

Imagine the world's
longest suspension bridge

stretching between
two mountaintops.

Picture it
311 feet up in the air,

miles from anywhere,

and with views across one of
the most picturesque landscapes

in all of Eastern Europe.

"Sounds totally awesome, Jay!

But would anybody really go
and build something like that?"

In Czechia, they already did.

[music]

[Jay] The beautiful
Králicky SneOník Mountains

lie in Eastern Europe.

A magnet for skiers
drawn by the great snow

and stunning views,

the area has
prospered as a resort.

[music]

[Jay] But with climate change
making the weather

less and less reliable,

they realized
they could no longer afford

to solely rely on the snow.

So, they decided to
create a mountain trail.

But this is no ordinary
stroll through the woods.

[music]

[Jay] At its heart
is a 2365-foot-long,

vertigo-inducing foot bridge

soaring between
two mountain ridges

312 feet above the valley below.

You can almost
imagine James Bond

hanging off the bottom of it,
being pursued by an enemy.

[Jay] It's the world's longest
suspension foot bridge,

built in one of the most
difficult locations possible.

It's the last place that
you can imagine finding

such an incredible
piece of engineering.

[Jay] It had to be tough
enough to cope with winds

of up to 134 miles per hour

and strong enough
to need no pylons

along almost half a mile
of walkway.

This is Sky Bridge 721.

So, how did they build it?

[music]

[Jay] The Ski Resort of
Doini Morava in Eastern Europe

got its first
ski lift in the 1970s.

And ever since,
the local economy

has relied on winter visitors.

But as winters get
warmer and shorter,

there's less and less snowfall.

[speaking foreign language]

[Jay] The resort
needs a solution

that will keep visitors coming
regardless of the snow.

Their audacious plan

is to create a walk
through the mountains,

but with a difference.

It will start on
a sky-high foot bridge

that stretches almost
half a mile across the valley,

strung between
two mountain peaks.

First, the engineers
will need to find a way

to support it at
either side of the valley

by building pylons strong enough

that it needs no support
along its length.

[music]

[Jay] Then they'll
need to figure out

how to connect the pylons

with lightweight
tension steel cables

designed to carry the weight
of the four-foot-wide deck.

They'll also have to engineer
a way of stabilizing the bridge

to help it cope with winds
of up to 134 miles per hour,

drastic temperature changes,

and wildly varying loads caused
by snowfall and visitor numbers.

If they succeed,

they'll have created the
longest suspension foot bridge

on the planet.

[music]

[Jay] More than 500 feet
longer than its nearest rival,

making it won't be easy.

Because bridges hang in midair,

there's nothing underneath them

to resist the pull of gravity.

So the longer they have to span,

the heavier that bridge is,

and therefore
the stronger that force is

that's pulling on it.

[Jay] It's a daunting
prospect for any engineer.

[speaking foreign language]

[speaking foreign language]

[Jay] Despite any concerns,
work begins in late 2020.

The first stage is to
design and build the system

to attach both ends of
the bridge to the mountain.

[Corina] The problem is, the
longer the suspension bridge,

the heavier it is,

and the pylons have
to be stronger.

So this is going to be
a very, very long bridge.

[Jay] Working at
two mountaintop sites

on opposite sides of the valley,

3,610 feet above sea level,

the team digs 30 feet
down into the bedrock

to create foundations
capable of taking the load.

Then, prefabricated
steel sections

are transported up
winding mountain roads

from the valley below...

before being bolted
and welded together

to create two
38-feet-tall steel pylons.

[music]

[Jay] After six months

and a whole lot of
concrete and steel,

the bridge's supports
are in place.

But the hard work
has only just begun

because somehow, they now need
to get 158 tons of cable strung

between two mountaintops

which are almost
half a mile apart.

[Dr. Mabry] In the past,
for a simple bridge

across a narrow gap,

they may have even
used a bow and arrow

to fire the first
pilot line over.

If you're over water,
you can use a boat

to carry the line across.

But neither of
those are gonna work

for a span over 2300 feet

between the two
towering mountains.

[music]

[Jay] Can 21st century
technology solve the problem?

[Jay] In Czechia,
engineers need to find a way

to string steel cables across
a half a mile-wide valley,

312 feet in the air.

The first step
is to get a pilot line

between the two pylons.

To span the huge distance,

they deploy some
21st century hardware.

[Dr. Mabry]
It's such a neat idea.

Once a drone has taken
the pilot line over,

you can attach a slightly
thicker cable to the end

and use pulleys to pull that
back across the valley.

You can then attach
another slightly thicker cable

to the end

and continue to pull it
across the valley

until you pull
the final cable over.

[music]

[Jay] It takes
three days of pulling

increasingly thick lines
across the valley.

But at last, they are
ready for the final cables.

As these steel wires,
each three inches thick,

half a mile long,
and weighing 23 tons,

are unraveled
300 feet in the air...

...they're vulnerable to winds

which can reach
134 miles per hour.

[speaking foreign language]

[Jay] It takes six long
weeks of careful stretching,

but finally, all six cables
can be attached at both ends.

It's a huge moment for the team.

[speaking foreign language]

[Jay] Now they have
to build the deck,

the most hair-raising
challenge yet.

244 sections,
each 10 feet by 4 feet,

have to be suspended
312 feet above the ground.

With no way to get
a crane into the valley,

the only way to do it is to
lay the walkway piece by piece

while suspended from the cables.

These guys are working
at 312 feet in the air.

That's the height of
the Statue of Liberty,

from the ground to
the torch in the air.

[Jay] Working simultaneously
from each end,

two teams lay
the deck piece by piece.

[music]

[Jay] It takes
10 weeks, but at last,

the deck is complete.

However, there is still one more
important challenge to come.

[speaking foreign language]

[Jay] The Sky Bridge
needs to handle temperatures

between minus 62 and 90 degrees.

[Dr. Mabry] Drastic
temperature changes

are a bridge engineer's nemesis.

Heat and cold can cause steel
cables to expand and contract

or stretch and shrink.

[speaking foreign language]

[Dr. Mabry] If cables start
to sag or tighten too much,

it could stress
the structure in ways

that it can't cope with,

potentially leading to collapse.

[Jay] To overcome this,

the engineers devise
an ingenious system of cables

which attach
the bridge to huge moveable

four-ton concrete blocks
on the valley floor.

As the bridge rises or
falls with the weather,

the blocks rise and fall too,

keeping the exact same
tension in the cables.

[Dr. Mabry] It's genius.

Such a simple idea,
but it allows the bridge

to react constantly to
the changing pressures on it.

Even better, it's practically
maintenance free.

[Jay] In May 2022,
the Sky Bridge

opens to anyone brave
enough to walk across.

I had to ask my
colleague to grab my arm

and to go with me.

If you see just
the bottom under you,

that's strange.
That's so crazy.

[Jay] Built in 18 months

and at a cost of almost
10 million US Dollars,

it's an enormous achievement.

[speaking foreign language]

[Jay] Open rain or shine,
the bridge was visited by

290,000 people in
its first year alone.

[speaking foreign language]

[music]

[Jay] The bridge isn't
just an incredible structure

in its own right;

it's transformed the
fortunes of this entire area.

It just goes to show what
great engineering can do.

[music]

[music]