Original subtitles

[Male Narrator] What happens when 41 stories

of radically futuristic design reshapes one of the world's most

recognizable and historic skylines?

I was described as public enemy number one.

[Narrator] How do you build a record-breaking bridge

without foundations?

These are the kinds of problems that keep bridge engineers

up at night.

[Narrator] And where do you begin with a gravity defying

cloud of glass and steel,

described as architectural chaos?

[Wolf] We can build everything

and not in the stupid way of doing boxes.

[music]

[Narrator] This is the age of the extraordinary.

[Haley] It's like one of those insect eating plants,

only enormous and white.

[Narrator] Where ingenious engineers have unleashed

unchecked creativity.

Now their secrets are revealed.

As we discover the inside stories of their construction.

This is an incredible feat of planning and engineering.

[Narrator] To try and understand,

"How Did They Build That?"

For our first building we're heading to England where

in 2001, one of the world's most celebrated architects

set out to create an extraordinary building

that would change the London skyline forever.

With the address 30 St. Mary Axe

it clearly needed a snappy nickname like the rocket.

No, no, no. The cigar.

No Jay. I know what we'll call it.

The Gherkin.

[Narrator] The City of London.

Home to the Bank of England since 1694

and a financial powerhouse ever since.

It's known for its traditional values

and until 20 odd years ago, its traditional architecture.

It's really hard to imagine now,

but apart from the Lloyds building

that financial district of London was architecturally

really quite dull.

[Narrator] Then at the very end of the last century,

the opportunity arose for a visionary architect

to change all that

with a building that would drag the city kicking and screaming

into a new millennium.

No one has ever seen a building this shape

and size anywhere in the world.

[Narrator] 41 stories of cutting-edge glass and steel

that was ruffling feathers before it was even

off the drawing board.

[Lord Foster] In the opinion page of a prominent newspaper,

I was described as public enemy number one.

[Narrator] An extraordinary concept that forced engineers

to use techniques never before tried

in a building of this kind.

This is 30 St Mary Axe.

Controversial, iconic and one of a kind.

It transformed the skyline of London forever

and challenged engineers to redefine the possible.

So how did they build it?

It's 1992, and a terrorist attack in the heart of the

city of London provides an unlikely catalyst for change.

A bomb is set off by the provisional

Irish Republican Army

killing three people and injuring 91 others.

It damages the Baltic Exchange,

a trading hall that had been at the heart of the city

for nearly 100 years.

The decision is taken to allow something

much bigger in its place.

Norman Foster, one of the world's most famous architects.

Responsible for the Millau viaduct in France,

and the Hearst Tower in New York,

takes up the challenge of redefining London's skyline.

[Lord Foster] Can it give something back to the city

of which it's a part?

In each of these buildings. They interact with the city.

They try to give something back to the public,

as well as creating something very, very special

for the private spaces within the building.

[Narrator] What Lord Foster has planned for the site

takes special to a whole new level.

A 180-meter tall, 57-meter-wide tower

completely in the round.

In order to reduce the impact at the ground,

it will get wider as it goes up

before being topped with a dome of glass.

An interlocking gridshell of two-story-high steel columns

will interconnect at 18 different points

every other floor.

It will then be covered in an intricate skin

made up of 7,492 panes of glass.

In an incredibly high-tech world,

here windows will simply open and close with the weather.

The passive cooling system will circulate air

through the building,

cutting down on air conditioning,

and giving it some seriously green credentials.

The Gherkin was an object of derision.

I think the name Gherkin originally was hostile.

In the opinion page of a prominent newspaper,

I was described as public enemy number one.

[Narrator] Despite the press being against the building,

in 2000 and with some trepidation,

the planning committee grants permission to go ahead.

A year later,

the construction teams break ground.

Arriving here and seeing the

enormity of the task was inspiring.

You really felt like you were getting involved

with something that was going to be out of this world.

[Narrator] The first challenge is to lay the foundations.

[Ellie] The base of the Gherkin is remarkably small,

but because it swells as it rises,

what you get is a very large building with a very small

ground-level impact.

[Narrator] It also creates a serious challenge

because it means the entire weight of the large building

is concentrated onto the small footprint.

Unable to spread the weight out,

the engineers have to create some heavy-duty foundations to

keep the building from sinking into the soft London clay.

Here you want to make sure foundation's sound.

People think that the building,

that the bits they see of the building is complicated.

There's an awful lot in the ground

that's similarly complicated that you will never see.

[Narrator] The team starts by drilling piles.

These underground columns measuring about

five and a half miles in total will hold the tower up.

Each has to be engineered to within an inch of its life.

The load was designed for 117 thousand tons.

We drilled 333 piles into the ground.

Collectively, that's nine kilometres

of straight shaft digging.

The London clay, it gets harder the further you go down.

And when I say hard,

it's like steel when you hit down on the bottom.

It is that hard.

[Narrator] With the piles drilled,

the team plans to finish the foundations with a massive

eight-feet deep concrete slab

connecting all 333 piles together.

It's absolutely crucial that the entire slab

cures at the same time.

No mean feat when you're pouring this much concrete.

You could end up with the bottom of the pile cap

curing before the top and it's not bonded together.

And that's not good.

[Narrator] The entire pour has to happen in one go.

And the concrete is specially treated to make sure none of it

cures till the last lot goes in.

There's an additive added to it,

which made sure that the first lot that got poured didn't

harden until the top part has.

So the whole lot could go off as one piece.

We had three concrete pumps, delivery pumps

situated on three of the corners

and we had 27 concrete trucks on turn around,

bringing this concrete in

from three different depots around London.

So it was a military maneuver that took just over 12 hours

of one continuous pour.

[Narrator] The crew pours over 63,000

cubic feet of concrete.

But with meticulous planning, it goes without a hitch.

Now with a solid base to build from,

the engineers get to work on the complex steel structure

that will hold the building up.

It's known as a diagrid.

The diagrid frame is a network of triangles,

which are also hugely strong and efficient,

but it also gives the building

that unmistakable trademark skin.

[Lord Foster] The Gherkin and the Hearst Building in New York,

when you look at them, they both have triangulated structures.

Why? Because a triangulated structure is inherently

more rigid with less material.

[Narrator] Constructing it is the next challenge

because this is one of the first times

a diagrid structure has been used to build a skyscraper.

[Rob Harrison] Everybody here really felt this is

the proper start to the project.

Everybody around the city, anybody who was coming past

was going to view this building rising from the ground.

[Narrator] The plan is to start with the core of the building,

which will act like the spine.

The steel diagrid structure will be built around it

and connected back to the core through a series of nodes

in the steel frame, like the spokes on a bicycle.

All watched carefully by the building's detractors.

[Paul Davies] The core itself was always six floors above

building the outside structure.

There were 18 of these frames per floor going around

before the next set come on top.

[Narrator] Then, as the building gets higher,

something strange starts to happen

that threatens the entire project.

[Paul Davies] Our engineering team started noticing

things weren't exactly where they should have been.

[music]

[Narrator] Next, the teams have to find out what's going on.

[Narrator] It's 2001, and in London, England,

work is underway to build a revolutionary new skyscraper,

but it's hit a major problem.

For some unknown reason, the structure is moving.

They have to find out why.

[Paul Davies] Our engineering team started noticing

a constant pattern of errors.

They did something in the afternoon,

the following morning when they checked it again,

things were out of where they... Out of plum.

[Narrator] After some serious detective work,

the team discovers the culprit.

London's famously changeable weather.

Steel changing its dimensions due to weather is a really

big challenge in construction.

[Narrator] When steel gets hot, it expands.

In cold, it contracts.

And that is exactly what's happening here.

In summer, in London it can be freezing cold one day

and then the next day you have blistering heat.

So the challenge becomes how do you calculate for temperatures

that you can't predict?

[Paul] The only way we could correct it

was getting the engineers to transfer working at night

when it was cold.

And by and large, not very windy.

[Narrator] And by doing just that,

they're able to get constant measurements

that overcome the problem.

But the challenges don't end there

because the engineers need to somehow counteract the building

moving under its own weight.

You've got the two and a half thousand tons worth of steel,

which gradually gets loaded. Each floor adds more weight.

That weight obviously compresses down.

And it's a bit like overeating. Your stomach comes out, yeah?

And it's exactly the same with this structure.

As the weight comes on

the circumference of the building grew.

And each level was designed to settle by 40mm.

It did that to perfection.

[Narrator] The frame is designed with an

extra bolt on each connection, so floor by floor,

once the building finishes settling,

the construction crews tighten them,

creating a completely rigid structure.

[Corina] The engineers who designed these steel frames

are getting so good at predicting deflection.

They can keep tolerance to a minimum

and so get narrower gaps in framework and the facades,

so you end up with a slicker finish.

[music]

[Narrator] The next challenge is getting that perfect finish

using almost 80,000 square feet of glass.

To pull it off, the team turns to what is at the time,

a revolutionary idea.

They use cutting-edge computer technology for the design.

The result is a pattern of 7,492 panes of glass,

but they fit without a hitch.

And somewhat strangely in a building

that's all about its curves,

7,491 of them are actually flat.

So the very last piece of glass to go in is the lens at the top

of the building, which was 2.4 meters in diameter,

250 kilograms.

And the actual capping piece of glass was lifted up

by a tower crane with the rope access guides going around it,

installing the pressure plates that hold it down.

[Narrator] This building is different in so many ways

from those that have come before it

and most that have been built since.

[Lord Foster] It's tighter at the base.

It swells out in the middle and it reaches a point in the sky,

which unusually is not devoted to mechanical equipment.

[Narrator] Most buildings have their air-conditioning units

on the roof.

The reason they sit outside on a roof,

it's so that they get free ventilation to them.

So bringing that inside the building was a challenge.

[Narrator] In order to pull this off,

Lord Foster needs a system of cooling the building

that does not completely rely on air conditioning.

It's genius is in its simplicity.

There's six triangular light wells on every floor.

There's four windows at the end of that light well.

They're triangular windows.

And they open up when the weather conditions are right.

[Narrator] If the building is getting too hot,

the automated glass hatches open up.

And if it's cold outside, the windows close

to retain the heat.

The pinecone, which opens and closes

according to the weather,

it's pulling air through the lungs of the building.

It's making it more healthy, fresher

and dramatically reducing the amount of energy.

Up to 50% less energy compared

with a convential building.

[Narrator] In December 2003, the Gherkin is finally complete.

Stunning on the outside

and inside, thanks to reducing the need for air conditioning,

there's a restaurant rather than a plant room at the top.

[Lord Foster] In that sense it's almost unique

because the top of the building is about the panaroma

of the city, the region.

It's for the people. It's not for the machinery.

[Ellie] That continuous, glazed domed roof

with those 360 views,

it is an exquisite design vision

only made possible by brilliant engineers.

[Paul] My personal feelings when we actually completed

was one of elation, pride.

It was the best four years of my life.

It's given an awful lot back to the city of London.

[Rob] Anybody who was involved in this building has

a huge amount of pride in it.

And its legacy will withstand

and will retain for many, many decades to come.

[Narrator] Born out of an atrocity,

and vilified before it was built,

30 St. Mary Axe has become a symbol of a new city of London.

A building that is as clever as it is beautiful.

A structure that challenged traditional thinking.

And one that has changed the skyline

for a very long time to come.

[music]

If I said I was gonna build a road bridge across a lake

a mile and a half wide,

but instead of securing the bridge to the riverbed

and supporting it with huge towers,

it would just float on the lake's surface

on 77 concrete pads.

You'd probably think that was a crazy idea.

The thing is, in Seattle,

one thing they really love is crazy ideas.

[Narrator] And on the surface, that's exactly how it sounds.

The problem was that Seattle desperately needed a new bridge

to get people in and out of the city.

But Lake Washington is so deep and the lake bed so soft,

that traditional bridge building is a no-no.

So they decided to construct the world's longest

and widest floating bridge.

It had to hold up a rigid road,

yet somehow move with the natural forces

of the water below.

Building it pushed engineers

into some seriously choppy waters.

These are the kinds of problems that keep bridge engineers

up at night.

[Narrator] They had to create a mega drydock from scratch

where they could construct the 77 enormous

concrete floating pontoons.

Any imperfection could lead to the pontoon sinking

to the bottom of Lake Washington.

[Narrator] Every piece had to be transported over 200 miles

through the Pacific Ocean.

This is the Evergreen Point Floating Bridge,

a record breaker that took world class engineering to realize.

So, how did they build it?

[Narrator] It's 1997, and in the pacific northwest,

the city of Seattle is growing bigger by the day.

A tech boom is attracting more and more people

making it one of the fastest growing cities in the US.

But its infrastructure is starting to creak.

And in particular,

an old bridge over Lake Washington,

a vital link to the city built in the 60's,

which can't cope with the volume of traffic.

There are regular backups for miles

and it's literally cracking under the weight.

With the existing bridge at the end of its life,

the designers find themselves in a race to replace it.

The weather, the traffic, the levels of the lake changing.

These are the kinds of problems that keep bridge engineers

awake at night.

[Narrator] Building this bridge over Lake Washington

poses a unique set of challenges.

Not only will it have to span over 1.4 miles,

but solid ground is hundreds of feet below the surface.

Don Oats is one of the design managers

tasked with coming up with solutions.

[Don] Lake Washington is a unique lake.

It's very deep. It's about 200 feet to the mud line,

because of the volcanic eruptions it's actually filled

with very, very soft soil to a depth of about 80 feet.

And then below that, you'd have to excavate down

about another 100 feet to be able to get to dirt

that you could actually build a structural foundation on.

[Nehemiah] If you went with the traditional suspension bridge

like, say, the Golden Gate Bridge,

you would end up with towers that are about 400 feet tall

before they even got out of the water.

[Corina] Then add another 600 to support

the suspension bridge roadway,

that's a 1,000-foot tall tower.

Not gonna happen.

[Narrator] The team takes inspiration from the old bridge

and decides to create a new supersized floating bridge.

This new bridge will have an extra four lanes

and room to expand to take a light railway

if it needs it in the future.

The road will be elevated above the pontoons

and cushioned with shock absorbers to stop the vibrations

from cracking the structure.

And everything will be balanced on top

of 77 floating concrete pontoons anchored to the lake bed below.

Now the engineers just need

to float hundreds of thousands of tons of concrete.

Making something that floats out of concrete

may seem quite unlikely,

but actually it's just simple physics.

Imagine this is concrete.

Guess what? It sinks.

But if I take the same amount of concrete

and shape it into a cup.

This time, it floats.

[Narrator] Even though making the enormous concrete

bridge float is possible,

constructing the giant pontoons creates its

own set of challenges.

Firstly, they need a massive dry dock in order to build them.

A dry dock helps you build a boat

or in this case, our pontoon

in what is essentially a giant empty bathtub.

When the pontoon is ready to float,

the dry dock is flooded by lowering a massive gate

and the pontoon can float out.

[Don] We figured out it needed a basin about

900 feet long by 200 feet wide.

[Narrator] It's a huge area,

roughly the size of six soccer fields.

Which is not exactly easy to come by in a busy bustling city.

In the end, the team finds a disused lumber yard

80 miles away in the coastal town of Aberdeen.

Not exactly local,

it proves to be one of the few places available

to build the enormous dry dock.

Overseeing construction of the pontoons

and the brand new $367 million dry dock is Phil Wallace.

This is our 55-acre casting basin that we had

down in Aberdeen, Washington.

This basin was built, so we could cast six pontoons.

So four along two pontoons

and two of the auxiliaries in the back.

We put in a gate in this area here to allow the pontoons

to float out.

We had over 600 employees working there

at different times a day, working days and nights.

[Narrator] With the dry dock ready,

work starts on building the pontoons,

which will be cast using over half a billion pounds

of concrete.

To make the pontoons, the engineers built a

massive mold known as formwork.

Then they started pumping in concrete to fill it.

This is a critical stage on any build.

[Ellie] Any imperfection could lead to a fault,

then a fracture.

And then ultimately,

to the pontoon sinking to the bottom of Lake Washington.

They're like 200 tons a piece. Everything is big.

The most critical pour that goes in is the wall form pour,

the exterior wall of the pontoon.

In that pour,

you need to make sure you have a good joint at the bottom.

[Narrator] Although the team strives

to make each pontoon perfect,

they're designed with the worst-case scenario in mind.

Instead of being a single large space,

they're divided into sealed compartments,

so if one leaks,

the others can still do their job.

So we're currently inside one of the larger pontoon cells,

and you see hatches to the adjacent cells.

All of these hatches are watertight.

So keeps the cells separated in case there's any water

entering any of these cells.

So all of that is connected to the pontoon-monitoring system.

So there's alarms trigger

in case any of these cells need to be pumped out.

[Narrator] It takes months, but eventually,

the pontoons are completed and moored at a nearby harbor.

But before they can be transported to Seattle,

the engineers need to create a system for anchoring them

in place once they get them there.

One that can cope with the varied lake bed

and the forces of the water.

[Don] There were three different types of anchors

for the different soil conditions that we had.

The shaft anchor, eight-foot diameter steel shafts

that go into the ground filled with concrete and a steel cage.

[Narrator] The next anchor type is nicknamed the box of rocks.

That are literally 40 by 40 by 20 foot tall.

They look a lot like pontoons, but they're open top.

They are 600 tons with all the rock in them.

[Narrator] The last are like a supersized,

traditional ship's anchor.

45 will be used on the bridge.

[Don] All the anchors we had to test for loads

up to about 570 tons.

So it's a massive load that these anchors can take.

[Narrator] The pontoons are cast.

The anchors are set.

It's now time to tow them the 260 nautical miles

around the coast and into Lake Washington.

But this means going out into the open sea.

Here the 360 by 75 foot pontoons will be at the mercy

of the Pacific Ocean.

[Narrator] In the pacific northwest,

engineers are planning to transport massive cement

pontoons through open ocean

to construct the world's longest floating bridge in Seattle.

You got big tractor tugs that take them up the coast.

We didn't float them until we knew we had a nice window

where we weren't going to have any storm conditions.

We generally could go four knots.

That was probably the maximum speed those pontoons could take.

So you're out there, you know, a couple of days in the ocean.

[Narrator] Moving each pontoon takes around two days,

but finally the 77 are in place.

Now the engineers face their next challenge.

Although the pontoons are anchored,

they move with the water of the lake.

Somehow, they have to figure out

how to fix this constantly moving bridge

to the rest of the highway, which is fixed on land.

[Nehemiah] Fixing the stationary structure to a moving one

is incredibly difficult.

In this case, that structure is floating on a lake.

All kinds of things can happen to make that structure move.

[Don] The transition span was one of the more complicated

pieces of infrastructure we had to build.

The floating infrastructure moves,

fixed structure hopefully, does not.

And so you have to figure out how to connect that.

[Narrator] They turn to automotive engineering

for a solution.

We put it on what we called a large trailer hitch.

Just like a tow hitch, this has spherical bearings

that let the floating section of the bridge move up and down

and side to side.

It's these that keep the bridge from tearing itself apart.

[Narrator] With each pontoon connected

by massive bolts and cables.

A raised roadway is added to the top of the pontoons.

To prevent it from cracking,

the entire six lane wide road sits on special shock absorbers.

So we're currently standing on one of the longer,

longer channel pontoon.

This is 360 feet, so about the length of a football field.

This makes a majority of the foundation that's

holding up the bridge structure above us.

You can see on all the columns here,

there is a bearing sitting on them,

so it allows for a little bit of movement there in the road sway.

Those are pretty much cushions that the roadway is sitting on.

And so along the entire bridge, you can see there's

hundreds of these holding up the bridge stacked

on top of all the columns.

[Narrator] Finally, after four years,

this 1.4 mile long record-breaking floating bridge

is in place.

And the first people who get to use it,

are the families of the dedicated men and women

who helped build it.

We actually had a family day where all the workers

that had worked on the job were invited out to walk the bridge.

So the people that built the bridge,

actually get to see it first.

And then a couple of days later the state had a big celebration

and over 50,000 people showed up for that celebration.

[Don] I mean, there were some hard times

and we went through some really stressful events.

And some ones that you kind of laugh at now

when you kind of think back at them,

but there's a lot of pride that we have from it.

[Narrator] This simple ribbon of road

hides its importance as a marvel of innovation and engineering.

While for locals, it's a lifesaver,

giving them back all those hours

that would otherwise have been spent

sitting in a traffic jam.

[music]

As in all fields of creativity,

it's easy to think that surely by now everything possible

in architecture has been done.

I mean, there can't be any more genuinely original ideas, right?

But back in 2001, a call went out

to design a new museum of science and anthropology

for the French city of Lyon.

The opinion-splitting building

which resulted was totally unlike anything

that had gone before.

Nor has there been anything else like it ever since.

Mold-breaking design classic or just architectural chaos?

You decide.

[Narrator] Take one tiny spit of reclaimed land

sitting where two rivers join.

We said we should move it.

The government said, no, no way.

[Narrator] A French city that wanted to create a building

for which it would be remembered.

[Corina] A building that's a cloud

with a whirlpool in its ceiling?

Only in France.

[Narrator] And an architect with a passion for the extraordinary,

and a hatred of the ordinary.

I basically, I hate columns.

[Narrator] And what they got was a building so complex

that even its designers couldn't predict the final result.

And where, from the metallic cloud-like front

to its crystalline back,

every piece seemed more complicated than the last.

[Marcus] Even for us architects is how will it really look like?

[Narrator] Nicknamed the cloud,

This is the Musée des Confluences,

a gravity-defying, mercurial structure,

which would push both architects and engineers

to realize the impossible.

So how did they build it?

In 2001, the rather traditional city of Lyon

decides that it's going to bring new life to a small,

neglected part of the city.

A thin spit of land

that was created over 100 years ago

and sits where the Saone and the Rhone rivers meet.

Until now,

it's been little more than a local picnic spot,

but the city has bigger plans.

They want a centerpiece to attract new investment

to the city on both sides of the river.

And decide on a new museum building

to symbolise the coming together of the two rivers

with a meeting of minds.

Now all they need is a design.

They turn to award-winning architect, Wolf Prix.

Whose buildings are as extraordinary

as they are beautiful.

The Musée de Confluences is going to be no exception.

We can build everything

and not in the stupid way of doing boxes.

We try to liberate space.

It is not a museum.

It's a cloud where knowledge is traded.

[Narrator] The city only puts one constraint on the design.

It mustn't block public access to the end of point.

The land is so narrow,

this could seriously restrict what they can build.

But Wolf has an idea.

[Wolf] The concept of the building was

not only to organize the exhibition spaces,

but to lift up the building so that people can walk

to the point of confluence and the park here.

[Narrator] The final design is a gravity-defying building

that lays down the gauntlet to the engineers.

How can we build it?

Because it was like a flying building.

You have no idea how you can work with the architect

just to understand what is what is willing?

What is the objective of the architect?

[Narrator] It's clearly going to be

an enormous challenge for the team.

First, they will need to build a solid base

that's strong enough to support the weight of the building,

while holding up the huge columns

that will make it appear to float.

Next, they will have to construct a steel frame,

which will rest on top

and be covered in 64,000 square feet

of stainless-steel sheets to create Wolf's cloud.

Finally, they will build the crystal.

A spectacular entrance made from flowing glass panels

set into a thin steel frame.

At its heart will be a whirlpool,

108 feet high,

and built of specially curved glass.

It's known as the gravity well.

In 2010, construction begins.

And immediately the team faces a major challenge.

They may have plans for an extraordinary modern building,

but they're expected to build it on land that literally sucks.

Building on reclaimed land can potentially run

into all kinds of issues.

That area may be more prone to flooding.

And because that land may have once been a river,

it might be more unstable and prone to subsidence.

[music]

[Narrator] Next,

even the architect has second thoughts.

[Narrator] In 2010, in Lyon, France,

work is underway to build a magnificent new museum.

The only problem is, it's on reclaimed land

made up of loose sand.

They said we should move it.

The government said, no, no way.

This is the most important point in this city.

[Narrator] So engineers design foundations,

which include 570 deep piles

with a reinforced concrete slab sitting on top.

Onto that,

they plan to fix the columns to hold up the massive cloud.

[Markus] We had to put a lot of piles in to reinforce the earth.

We also lifted up, even the plinth,

the concrete part of this building

to be over the ground water.

[Narrator] It takes time and an awful lot of concrete.

But there are now solid foundations.

The next big challenge is to work out how on earth

they're going to build the enormous, show-stopping cloud.

To make it appear to float,

they take inspiration from an old-world engineering idea.

Construction of the cloud is the construction of a bridge.

[Ellie] A girder bridge is perhaps the most classic bridge

design that you and I are most familiar with.

The bridge deck is held up by huge iron or concrete girders

that transfer the load to the supporting columns.

[Narrator] At its heart, the complex floating structure

is made up of a series of interconnecting steel beams.

These allow the team to create the unique cloud-like shape.

And just like a bridge,

the forces from this are transferred to the ground

through a series of columns.

But its extraordinary irregular shape

makes it difficult to calculate how the loads will work.

A miscalculation could lead to the engineering failing

and the building collapsing.

The cloud is very hard to understand

and to describe because it's a cloud.

So how do you describe the shape of the cloud is not possible.

[Narrator] Hoping to make the impossible, possible,

the team tries to build a computer model,

but even that's not easy.

You let the computer working one day,

you come back after one day, you look at it,

and it doesn't function.

You have to try another solution,

but you wait always one day

to have the response of your idea.

[Narrator] Eventually, after some serious number crunching,

the engineers arrive at a structure that is as stable

as it is breathtaking.

The construction crew gets to work building it.

Here you have really complex connections of this different

secondary steel structures.

It worked well due to this really

sophisticated 3D model.

[Narrator] Once the main steel frame in place,

the team then creates its irregular shape

by constructing a smaller frame on top,

which is clad in 64,000 square feet

of stainless-steel paneling.

The next challenge facing the team

is how they're going to build the crystal,

a massive glass atrium, which will go at the front.

A challenge Wolf isn't making any easier.

Basically, I hate columns.

To solve a stupid column

in many parts was the goal.

[Narrator] Wolf wants to have an open space.

But it's vast and they need to find a way to support the roof.

Because of this interaction between all the elements,

it was very hard to achieve

the structural design of the crystal.

[Narrator] The solution for how to support the roof

lies in an extraordinary idea.

Imagination comes from, from the turbulences

when two rivers coming together.

This is the experiment, we did in our office

to see how a turbulence look like when two streams

coming together.

Then this is the plan.

It's the columns not being a column.

[Narrator] Wolf's idea is to create a support

that doesn't look like a column.

So they make a void in the middle of the atrium,

almost as if a giant finger has pushed the roof down

to touch the floor.

Constructed from glass and steel it looks perfectly in place

with the rest of the structure,

but it's also supporting the entire roof.

The extraordinary mix of sculpture and engineering

is nicknamed the gravity well.

If your structure contains a cone-like shape that's

tapered to the ground,

the forces will be transferred to the apex or tip of that cone.

So this shape is not only interesting architecturally,

it also serves a structural purpose.

[Narrator] The next challenge,

is making the structure strong enough to be able to deal

with 15 feet of snow.

They start with a cladding

of specially reinforced glass panels.

But the clever engineering doesn't stop there.

[Marcus] We have in the lower parts,

we have heated glass panels.

And the drainage is also heated

and the structure is strong enough

to take the pressure of snow.

[Narrator] Finally in 2014, after four years of construction

the Musée de Confluences is complete,

and the results are extraordinary.

It's a very open special,

not museum.

It's a building for trading knowledge.

[Marcus] I'm very, very, very proud.

And it was really great to be part of this team.

[Gabriel] Maybe one time in your life,

you make this kind of project.

So all your life,

you will remember and you will remember this experience.

[Narrator] This cutting-edge design transforms

what a museum can be,

creating an open, welcoming space that beckons people in.

And just like the two rivers that surround it,

it will bring people together for years to come.