Original subtitles

[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]