Original subtitles

Today on "Impossible engineering,"

the Millau viaduct, the tallest bridge on earth...

Rising 1,000 feet over one of Europe's deepest valleys...

Built on pioneering innovations from the past...

All right, now, this is what I'm talkin' about.

Today, the stromsund bridge is

a real landmark breakthrough in the world of engineering.

...To make the impossible possible.

Captions by vitac www.Vitac.Com

captions paid for by Discovery communications

Nestled in the Southern corner of the massif central in France

is the tranquil medieval town of Millau.

But every summer, that tranquility is shattered.

Millau lies directly in the path of the busiest travel route

between Paris and the mediterranean coast.

To free Millau from this plague of traffic,

engineer Michel Virlogeux is attempting

what was previously thought to be impossible...

build a road high above Millau

across the gargantuan Tarn valley.

The result...

the Millau viaduct,

the tallest bridge on earth.

This massive bridge spans a staggering 1 1/2 miles,

towering over 500 feet above the Tarn valley.

Just seven concrete piers support

the 40,000-ton steel deck,

which is held in place by a single row

of 154 super-strength cable stays.

Michel had to design a bridge that could span

one of Europe's deepest, widest, and windiest canyons,

using an uneven valley floor as a foundation.

To build the tallest bridge on earth,

Michel and his team need strong building materials,

something that would be impossible

without help from the great innovators of the past.

Man's earliest building materials were sourced

from nature.

Neanderthals built shelters from the bones

and tusks of wooly mammoths.

Mongolian nomads used sheep wool

to line the walls of their yurts.

And from the time of ancient civilizations,

many houses have been built with straw and clay bricks...

Reinforced with a touch of animal dung,

which works perfectly...

as long as you're standing in the right place.

To create a truly enduring structure,

engineers at Millau would look to the achievements made

by a British civil engineer 250 years ago.

Professor Luke Bisby is heading out into the English channel

to visit what's left of a truly revolutionary structure.

I'm heading out to the Eddystone,

one of the most treacherous rocks

in the English channel.

It's a place that arguably marks one of the most important

moments in civil-engineering history.

Today sits a 50-meter-tall lighthouse

designed by James douglass in 1882.

Amazingly, this is the fourth lighthouse

that's stood in this spot.

Eddystone rock is 14 miles from the busy port of Plymouth.

The rock has sunk countless ships

over the centuries.

In the 17th century,

a lighthouse was built to warn passing vessels.

A building that could withstand

the elements out here, the pounding of the waves

day after day and the wind and the rain,

requires a real engineering achievement.

In 1696, Henry Winstanley built

the world's first offshore lighthouse.

It was an 82-foot wooden tower.

But just 7 years later, it was obliterated by a storm.

Its replacement survived 47 years.

But that too was destroyed by the elements,

this time by fire.

If a lighthouse was gonna last any substantial amount of time

out here, a new engineering solution was needed.

Engineer John Smeaton had a unique idea

for the Eddystone lighthouse.

He believed that the sea must give way to the building

and decided to build a lighthouse made of stone.

It was how Smeaton joined the stones together

that was truly revolutionary,

earning him the title

"the father of civil engineering."

Smeaton's original lighthouse stood on this spot

for over 120 years.

And, in fact, we can still see the bottom half of it

as that stump of a lighthouse over there.

Smeaton's structure was so strong,

it was only cracks in the rocks that it sat on

that forced engineers to dismantle the lighthouse

and rebuild it on Plymouth hoe.

The secret to Smeaton's success is

an innovative bonding material that can survive

the constant pounding of the sea.

Smeaton experimented with mixtures of lime,

Clay, and iron slag to create hydraulic lime.

I'm gonna try to demonstrate the innovation

that Smeaton accomplished at the tower.

Here we have a traditional cob mortar.

This is a mixture of sand and clay and straw

and lime and a bit of earth.

And these types of mortars were used traditionally

for many hundreds and thousands of years.

And the other material that I have here

is Smeaton's mixture.

Luke places Smeaton's hydraulic lime

inside a cardboard tube,

then places the tube in water.

And then I'm also gonna do the same

with the traditional earth mixture.

Got both tubes now filled with the mortar.

We're gonna go away for about a half an hour.

And then we're gonna come back, and hopefully, we'll see

a pretty dramatic difference

in terms of how they've performed.

First, we're gonna look at the tube that's filled

with the traditional mud mortar.

We're gonna see exactly how much it's set.

And you can see... absolutely nothing.

This is the one we're much more interested in.

This is the one with the mortar

that's based on the hydraulic-lime technology

that Smeaton came up with.

I can immediately feel that this one is much more solid.

I squeeze it. Nothing happens.

If I have a look inside,

I can actually see this now is very, very solid.

That combination of setting very quickly

and setting underwater completely revolutionized

civil engineering.

What Smeaton had created

was the precursor to Portland cement.

Portland cement's the key ingredient

in all modern concrete.

The strength of Smeaton's hydraulic lime

allowed engineers to stack nearly 1,500 blocks of granite,

creating a rock-solid structure that could stand up

against the forces of nature...

so solid, in fact, the victorians couldn't

dismantle the base when the lighthouse was relocated

to Plymouth hoe over 100 years ago.

So here we have the original 250-year-old granite blocks

re-assembled here on Plymouth hoe

with mortar much like the original mortar.

Incredible that it still looks so good.

And if I look really carefully,

way out there on the horizon,

I can just see the base of Smeaton's original tower

standing next to the new tower.

This was really the game-changer

in concrete engineering worldwide.

The engineers at the Millau viaduct

are using John Smeaton's hydraulic-lime technology...

On an epic scale

...To build seven of the tallest bridge piers

on the planet.

The Millau viaduct, soaring high

above the French countryside...

it's the world's tallest bridge.

To support this engineering marvel,

its designers had to construct

seven of the tallest bridge piers on earth.

Chief engineer Michel Virlogeux had

just 4 years to finish the bridge

or face fines of up to $30,000 per day.

So, to save time, each pier was built simultaneously

at seven individual work sites.

Due to the uneven valley floor,

each pier is constructed at a different height,

the tallest a record-breaking 804 feet.

Their octagonal shape tapers gradually,

splitting around 300 feet below deck height

for added flexibility.

Engineers built each pier in 13-foot sections

using a self-climbing frame.

A hydraulic-driven system pushed the giant concrete mold

up in stages.

Cranes lift buckets of concrete,

which is then poured into the concrete mold.

After each pour has set, the mold is dismantled.

The frame carrying the mold

is then mechanically pushed by the hydraulic Jacks

up the piers

and re-anchored in the set concrete.

The mold is then re-assembled for the next pour.

Each cycle takes about 3 days.

The piers are completed ahead of schedule,

in just over 2 years.

With the bridge piers complete, Michel is ready to tackle

his next challenge...

construct Millau's 1 1/2-mile-long bridge deck,

long enough to span the vast Tarn valley...

...creating even more impossible engineering.

The Millau viaduct in southwest France

is an engineering wonder of the modern world.

At 1,125 feet, this superstructure stands taller

than any other bridge on earth.

The staggering height of the bridge presents

a unique challenge for chief engineer Michel Virlogeux.

How do you make the world's tallest bridge stable enough

to handle the hurricane-force winds

high above the town of Millau?

Protecting the Millau viaduct's bridge deck from high winds

would be impossible without an ingenious innovation

made by a civil engineer a half-century ago.

Professor Luke Bisby is exploring

one of britain's most iconic bridges.

All right, now this is what I'm talking about.

A vertigo-inducing 135 meters below me lies

the severn bridge.

The severn bridge provides a vital link

between England and south Wales.

The main section of the bridge is

over 1,598 meters long, which, at the time,

made it the longest bridge in the world.

I can actually see through this hole

about 1,000 meters down the bridge.

It's absolutely incredible.

The length of the bridge is impressive,

but its ability to resist the high winds

that frequent the river severn is

what makes this structure revolutionary.

Lying inland from the Atlantic ocean,

the river severn begins where the Bristol channel ends.

The high ground of exmoor on the south shore

and the mountains of Wales on the north

create a funnel for the prevailing westerly winds

and Atlantic storms, increasing their power.

Building a bridge that could withstand

severe winds was really essential.

And even on a relatively calm day,

standing here, underneath the bridge,

you really get a sense of the wind

that they were up against.

Civil engineer sir Gilbert Roberts was tasked

with building a bridge across the river severn.

His biggest innovation was a windproof bridge deck.

If you look at the shape of the deck,

you can start to get a sense of what the solution was.

And the most amazing thing is that the shape

of this bridge deck and the solution they came up with

was actually a happy mistake.

Sir Gilbert Roberts broke

his original truss-lattsign

while testing it in a wind tunnel.

As he waited for a replacement model,

he researched the aerodynamics of other objects,

leading him to a truly groundbreaking idea.

So, what I have here is a model airplane.

And you can imagine that the wing of this airplane

is representing the bridge deck.

So a wing has a curved surface on the top.

And it has a flat surface on the bottom.

And this means that air passing over the wing

has to travel further across the top

than on the bottom.

As air passes over the curved surface,

it speeds up and loses pressure.

The pressure of the air below remains high

and pushes up towards the low-pressure area,

creating lift.

What I'm gonna attempt to show you is,

with this hair dryer, to generate some wind,

the force of the little model airplane will decrease.

And that decrease will signify the...

the lift force that we've generated on the model.

There, we have our starting weight... 45 grams.

Right, so, there we go.

The engineers here didn't want that to happen

to the bridge deck.

When Luke flips the airplane over,

the lift affect is reversed, creating a downward force.

What we should see is that this force should increase

rather than decrease.

You can actually see the downward force

that's coming from the wind.

And that holds everything nice and taut and safe

in very strong winds.

Now that the curved surface is underneath,

air loses pressure as it speeds up.

And the high pressure above presses down.

And, of course, this is exactly the principle

that the engineers used on the severn bridge.

Sir Gilbert Roberts and his team created

an aerodynamic, steel-box girder deck,

the first of its kind in the world.

Hollow and only 10 feet deep,

the shape of the deck creates a wind flow

that holds it firmly in place.

Over the years, 13 vehicles

have blown over while crossing the severn bridge.

But the bridge itself has always held on strong.

Although this beautiful bridge has passed on

the burden of heavy traffic to its youngest brother

just downstream,

it still managed to carry more than 300 million vehicles

since it was first constructed in 1966.

And thanks to sir Gilbert Roberts

and his team, it's set to do so for many more years to come.

Engineers at the Millau viaduct have

created a bridge deck that's over 3,000 feet longer

than the severn bridge deck

and weighs a colossal 40,000 tons,

making it one of the longest on earth.

The deck's shallow, trapezoid shape creates

an inverse aerofoil

resulting in negative lift in strong winds.

To build Millau's colossal steel deck,

engineers had to assemble it in pieces

like a gigantic, steel Jigsaw puzzle.

The pieces were cut in factories all across France

before being transported to Millau.

Staging areas are set up

on each side of the valley to receive the deck parts.

Two thousand convoys loaded with cut steel make

the journey to Millau.

Welders use a staggering 165 tons of material

to assemble the massive bridge deck.

Engineers are ready to tackle their biggest challenge yet...

moving the deck sections from the staging area

to their final resting place

hundreds of feet above the Tarn valley.

The Millau viaduct in France is

a work of engineering virtuosity.

It's over 8,000 feet long

and taller than the Eiffel Tower.

For engineer Michel Virlogeux,

building this gargantuan structure is

the challenge of a lifetime.

Michel's biggest challenge... figure out a way

to move the bridge's 1 1/2-mile steel deck

from the staging area

out into the open air high above the Tarn valley.

The extreme height of the piers rule out using a crane.

The only option for engineers is to try to slide the two massive

sections of deck together from each side of the valley.

The leading edge of the deck weighs 7,700 tons.

The pier's great height-to-width ratio means

they're susceptible to lateral forces.

Pushing the deck across the pier's surface

will create friction, increasing the lateral force

with potentially disastrous consequences.

Michel needs to reduce friction during the launch process,

a task that would be impossible

without help from an accidental innovation from the past.

Friction has been a sticking point for builders

for thousands of years.

Heave, ho. Heave, ho.

Ancient Egyptians struggling to slide their blocks

across sand...

Realized water created a smoother, slicker surface...

Whoo-hoo!

...although too much was not advisable.

D'ohh!

It's believed the builders of the stonehenge

rolled their giant rocks across a series of logs.

- Aah! - Ooh!

It was the perfect solution, as long as the ground was flat.

Look out!

For the engineers of Millau viaduct,

a scientific mishap made in a U.S. laboratory

in the 1930s is their solution.

Most people will recognize these day-to-day objects.

But what most people don't know

is that all of these harness the same properties

of a revolutionary product called PTFE

or, to give it its full name, polytetrafluoroethylene.

This groundbreaking product was mistakenly created in 1938

by an American chemist, Roy Plunkett.

Roy was experimenting with a gas, tetrafluoroethylene,

when it unexpectedly solidified, coating the inside

of a test tube with a waxy resin.

Plunkett had created what would eventually become teflon.

It has lots of different properties.

It's very corrosion-resistant.

It's chemically inert.

It doesn't react with other materials.

And it has a very high melting temperature.

But above all of these, it's very, very slippery.

And being slippery means that teflon is a great tool

for overcoming the forces of friction,

something that's hard to do with a standard metal.

So, here I have a sled connected to a metal tray underneath

and about 45 kilos of bricks and sand.

And as I pull the sled along,

the tray is gonna have a huge amount of friction

against the metal sheet here.

And that friction is retarding the motion.

As I start to pull against this now,

you can see I've got 5 kilograms.

And I've still got no movement.

So that's the friction preventing my sled from moving.

I'm up to 7 kilograms,

10 kilograms, 11, 12.

And there it goes.

Ugh.

So that's about 120 Newtons

of force to pull those along.

To see how PTFE performs,

a metal tray is prepared,

then sprayed with the slippery coating...

And cured at 430 degrees fahrenheit.

Wow. Look at that.

That looks incredibly smooth.

So let's give it a go.

I've got 2 kilograms, 5.

6, 7, and, look... it's starting to move already.

Seven kilograms here to overcome the friction.

When you compare that to 12 kilograms...

that's 120 Newtons.

So that's about 50 Newtons difference

to move the same amount of weight.

PTFE is made of carbon and fluorine atoms.

Fluorine has a high electronegativity,

meaning it repels other atoms.

The fluorine wraps around the carbon,

preventing the carbon from reacting

to any outside forces.

The result is a frictionless, slippery substance.

The sled can carry up to 40% more weight

when pulled across the PTFE-coated sheet,

"the equivalent of a 5'9" engineer.

- How much are we seeing? - 12.

There you go... 12 kilograms, 120 Newtons.

How about that?

Engineers at the Millau viaduct are using PTFE

in a unique mechanism that will launch

the massive bridge deck across the Tarn valley.

Called a translator, the machine uses

the slipperiness of PTFE and hydraulic Jacks

to lift the deck off each pier entirely

before moving it deeper into the valley.

Each translator uses

two wedge-shaped blocks coated in PTFE.

A hydraulic ram pulls the upper wedge,

which slides it up the lower wedge.

This lifts the deck away from the pier,

pushing it forward at the same time.

The lower wedge then slides backwards,

lowering the deck back onto the pier.

Each cycle moves the deck approximately 2 feet.

But as they prepare for their first launch attempt,

engineers hit a snag.

Seven temporary piers are built across the valley.

But as the 1 1/2-mile deck is pushed out into the void,

the course is not straightforward.

As the two colossal sections approach each other

from opposite sides of the valley.

Engineers rely on GPS technology to ensure pinpoint accuracy.

Fifteen months after the first attempt,

the two sections of deck finally meet above the Tarn valley.

And, incredibly, they're only off

by a few millimeters.

But to ensure the tallest bridge on earth survives

for generations to come, engineers are looking

to a groundbreaking innovation from the past...

Today, the bridge is considered a real landmark breakthrough

in the world of engineering.

...To create more impossible engineering.

The Millau viaduct is an engineering wonder.

Connecting the high plateaus of France's Tarn valley,

this audacious bridge is one of the tallest in the world

and one of the greatest engineering achievements

of all time.

For engineer Michel Virlogeux and architect Norman Foster,

the bridge's environmental impact

on the French countryside is a top priority.

Unstable limestone in the region ruled out a suspension bridge,

which relies on firm anchor points

at each end to take the weight of the deck.

So for Michel, there was only one alternative.

Constructing a multi-span, cable-stay bridge

on such a huge scale would be impossible

without the groundbreaking work done by a German engineer

60 years ago.

Structural engineer jonatan ledin is paddling

the great stroms vattudal in Sweden, searching

for the source of a historic engineering breakthrough.

For centuries, this stretch of river here in stromsund

has been an obstacle that travelers needed to overcome.

In the early 1950s, it was decided

a suspension bridge should be built across the river.

But German engineer Franz dischinger had

a different idea.

Franz was a key player in rebuilding Europe

post-world war II,

where 15,000 Bridges were in need of repair.

Dischinger's construction techniques were

cost-effective and efficient.

What dischinger built was this, the stromsund bridge...

A cable-stay design that has since been recognized

as a landmark in engineering history.

A cable-stayed support system is simple but very effective.

Imagine my arms are cantilevering

out from my body like this.

And I'm trying to hold the buckets of water

in place like this.

I need to do a lot of work with my arms.

This is not exactly easy to hold onto.

I'm gonna use this rope here

to represent the stay cables attached to the bridge deck.

And I'm gonna pull that over my head,

which is representing the piers.

So now the majority of the weight

is no longer carried by my arms

but through the cables onto my head

and down to the ground.

And that is exactly what is going on behind us.

The weight from the bridge and the loads from traffic

are being transferred through the cables

and down onto the piers.

Early cable-stayed Bridges

were structurally weak.

Rudimentary cables and limited understanding

of the forces at play in the system meant,

by the early 19th century, the idea was nearly abandoned.

And a problem that the engineers were struggling with in the past

was designing the cables

so the loads would be distributed evenly among them.

The consequences of one or more cables

being overtensioned can potentially be disastrous.

Dischinger looked to mathematics for the solution.

He created formulas to calculate

the forces required of each cable.

Each of those cables was then precisely tensioned on site,

an engineering first.

After carrying vehicles for over 60 years,

dischinger's supporting cable stays are being replaced

for the first time.

Today's engineers are using

the exact same installation process dischinger used.

So, these are the brand-new cables

that are gonna be installed overnight.

And just as would have happened all those years ago,

they're first gonna be mounted in place

and then precisely tensioned.

Dischinger's innovative approach makes this possible

to do in just a few hours.

Post-world war ii engineer Franz dischinger's

pioneering construction techniques

have influenced some of the most iconic Bridges around the world,

including the massive Millau viaduct,

with its 1 1/2-mile-long cable-stayed bridge deck.

Dischinger's revolutionary stromsund bridge is

being restored to its former glory using

the exact same techniques

dischinger used a half century ago.

So the work has been going on here on site all night.

The way in which all of this is being done

is really not that different

from what would have taken place here all those years ago.

So, today, the stromsund bridge is considered

the first true modern cable-stay bridge

and the real landmark breakthrough

in the world of engineering.

Engineers at Millau have taken

dischinger's methods to the next level,

creating a structural masterpiece.

Dischinger's stromsund bridge has only one central span.

The massive Millau viaduct... six.

As the 770-ton pylons are erected,

engineers had to calculate the perfect distribution

of rigidity and flexibility throughout the structure.

The key to their success lay with the cable stays themselves.

The strongest cables are made of 91 steel strands

and have a breaking strength of over 2,000 tons.

They're so strong,

engineers install just a single axis,

and only when tensioned did the entire bridge become rigid.

After a little more than 3 years of construction,

the integrity of the bridge can now be tested.

Twenty-eight trucks weighing a total of 900 tons

are driven en masse to the center.

The deck flexes, but only a few inches.

The bridge remains firm.

Finished 2 months ahead of schedule,

the Millau viaduct

marks a significant milestone in bridge engineering.

It's used by nearly 5 million vehicles a year.

For engineer Michel Virlogeux,

it represents the achievement of a lifetime.

By learning from the great pioneers of the past,

adapting, upscaling, and making innovations of their own,

engineers succeeded in making the impossible...

Possible.

Many thought that it would be impossible

to build that bridge, and now it is there.

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