Original subtitles

Today on "Impossible engineering,"

the Rion-Antirion bridge...

A colossal structure built in the heart of an earthquake zone.

Spanning 2 miles across open water,

it took revolutionary engineering...

...and a look back at some hard lessons from the past...

The energy release was massive,

and now the specimen has just catastrophically failed.

...To make the impossible... Possible.

Captions by vitac

captions paid for by Discovery communications

August 2004, the Rion-Antirion bridge

opens to traffic for the first time.

It's an engineering masterpiece of the modern age.

This massive structure

spans almost 2 miles across the Gulf of Corinth in Greece.

It boasts the longest fully suspended deck

and deepest foundation piers of any bridge on earth.

For chief engineer Panayotis Papanikolas,

it was the project of a lifetime...

...but for centuries,

building a bridge across the Gulf of Corinth was just a dream

due to a long list of environmental challenges.

But wind isn't the only threat to the bridge.

The two land masses on either side of the Gulf of Corinth

are constantly drifting apart.

This, along with frequent earthquakes, high winds,

and deep water meant that

building a bridge across the Gulf would be a daunting task...

...but the need for a safe crossing was desperate.

The perilous waters of the Gulf of Corinth

often made ferry crossings impossible

and cut the peninsula off from important services.

So in the 1990s, the government embarked

on one of the most ambitious engineering projects

in modern history.

The first challenge was to design a bridge

that could span

the almost 2-mile gap across the Gulf of Corinth.

The distance was too great for a single-span bridge,

so engineers has to build support towers in water

that's over 200 feet deep.

To overcome the water-depth issue,

Panayotis and his fellow engineers

would need to look

to history's great engineering innovations for the solution.

Building in water has always been a challenge.

Early builders relied on conveniently placed rocks

for the foundation of their structures.

Fine for lighthouses, useless for bridge building.

Creating artificial islands

was time-consuming and impractical in deep water.

In the 19th century, pressurized structures called case-ins

were developed to create underwater building sites.

But they were difficult to build...

And dangerous.

Fortunately, in the 20th century,

a new technique was on the horizon.

In the 1940s, engineer guy Maunsell

came up with a solution

that finally conquered the challenge of building at sea.

Professor Luke Bisby is heading far out into the English channel

to see the remains

of Guy Maunsell's bold creation firsthand.

Maunsell's influence on contemporary engineering

I don't think really can be overstated.

This was really the first time

that this had ever been attempted,

and so it was really quite a daring feat of engineering.

Maunsell's innovation

was triggered by the second world war.

It became clear the river thames was a prime target

for German bombers during the war.

The Germans wanted to destroy London's docks

and lay mines to disrupt allied shipping.

So Maunsell came up with a radical new design

for off-shore sea defense...

...naval forts consisting of two 80-foot high concrete towers

each containing four floors of accommodations

topped with a gun deck.

But the ingenious part of Maunsell's design

wasn't the layout of the fort...

It was how it would be constructed

and deployed at sea.

Knock John here was towed out 3 to 6 miles

from where it was constructed on land,

and then it was sunk in place exactly where you see it.

Maunsell designed the bases of his forts

as huge hollow concrete barges.

Despite their enormous weight,

they had enough buoyancy to float.

Maunsell built the forts

on top of these large concrete barges

and then calculated how large the barges needed to be

in order to hold the weight of the fort

so they could be taken out and then sunk in place.

The massive 4-1/2 ton concrete forts

were constructed in a dry dock,

then towed out to sea with a 100-man crew already on board.

When they had it in the place where they wanted it,

they essentially just pulled out a stopcock at one end

and let the water flow in.

As the water was flowing in,

the barge started to list in the water.

Eventually, the nose dipped under the water.

All 100 men were hanging on

as the fort was sinking at 35 degrees.

Despite the rough submersion,

Maunsell's groundbreaking design worked perfectly.

The bottom of the barge basically filled up with water,

and eventually the entire barge sunk to the bottom

and flattened out.

Maunsell's forts helped British forces shoot down

22 enemy aircraft and 30 flying bombs.

They protected London from attack

and made engineering history.

The influence of this type of construction you can see

in all different facets of engineering today.

You can see it in the off-shore-oil-and-gas industry

with oil platforms.

You can see it being used as foundations for wind turbines.

And, of course, you can see it being used

as a way of placing foundations

for large bridge structures around the world.

But the most impressive use

of Maunsell's revolutionary floating concrete design

is at the Rion-Antirion bridge.

The Rion-Antirion bridge

spans an incredible 2 miles

across the deep waters of the Gulf of Corinth.

To support this massive structure,

engineers used principles

first exploited by Guy Maunsell in the 1940s

and super-sized them.

In 1998, construction begins on 4 enormous pier foundations.

Each one is larger than a football field

and weighs almost 80,000 tons.

The hollow pier footings are built in a dry dock

just as guy Maunsell did

but on a scale he couldn't have imagined.

Before the footings can be taken out into the Gulf of Corinth,

engineers need a solution to a serious problem...

A problem Maunsell never had to deal with.

The Gulf of Corinth lies in the heart

of one of the most active seismic zones in the world.

In an earthquake, the soft seafloor would liquify

causing the piers to sink and the bridge to collapse.

Unless an answer was found, the project was over.

The engineers came up with a radical solution.

They would drive hundreds of long tubes deep into the soil

where the four piers will sit.

This ingenious idea stabilized the soft seafloor.

Bridge footings are usually

anchored directly into the ground.

But for the Rion-Antirion,

they were placed on top of a 10-foot layer of gravel.

This allowed the footings to shift with the earth

during an earthquake.

With a solution to the earthquake problem,

the engineers are now ready to begin

one of the most audacious parts of the build...

...maneuvering the half-constructed piers

into the Gulf.

Engineers continued to build up the massive structures

while they were still floating.

Each layer of heavy concrete that was added

sunk the pier further down,

pushing it closer to its final resting place

200 feet below on the seafloor.

The end result was four enormous hollow foundation piers.

They're the first of their kind...

A series of massive concrete underwater caverns.

The pier footings for the Rion-Antirion

can survive an earthquake,

but what about its nearly 2-mile long suspended deck?

The builders of this massive structure will need to produce

even more impossible engineering.

The Rion-Antirion bridge in Greece

is a modern engineering marvel.

Over 11 million cubic feet of concrete,

more than 100,000 tons of steel, and 39 miles of cabling

make up the longest fully suspended cable-stayed bridge

on the planet.

Panayotis Papanikolas and his fellow engineers

had to overcome a long list of obstacles

before their dream

of a bridge spanning the Gulf of Corinth

could be realized.

The Gulf of Corinth

is one of the busiest trade routes in Europe.

Its shipping lanes cannot be disrupted.

To design a bridge capable of spanning this gap

without interfering with shipping,

engineers would need to turn

to the great innovators of the past for inspiration.

It was the romans who first engineered solid Bridges

using stone and a simple but revolutionary shape... the arch.

However, the wider the gap,

the more arches were needed and the heavier the bridge became.

For hundreds of years, inca communities in the high andes

crossed gorges using suspended wooden walkways.

It's said that 16th-century Spanish conquistadors

arriving in Peru looked in amazement and fear

at the swaying Bridges that could break at any moment.

It wasn't until 1826 that a brilliant engineer

utilized new building materials and a new approach

to change the bridge game forever.

The Menai suspension bridge

is the ultimate achievement of Thomas telford...

One of britain's finest civil engineers.

Telford was an accomplished engineer.

Of course, at this stage,

he had designed canals and roads and Bridges.

He had never built anything on this scale before,

and so, this bridge was to be really his greatest challenge.

The Menai strait separates mainland Wales

from the island of Anglesey.

Centuries ago, bridging it would have been impossible.

A traditional Roman arch design would not only be enormous,

it would block the passage of tall ships along the waterway.

Imagine this as being the strait here,

and these are the valley walls on either side of the strait.

Basically, you cut your bits into shape,

and you then have to gradually build your arch,

adding the bits of the arch as you go.

And if you imagine that as now being the completed arch...

And we have our load coming along here...

You can see that the compression forces that come from that car

flow down through the various sections of the arch

and into the abutments on either side of the valley.

Now, the problem that telford faced

was that as you're building an arch,

you would have to have some supports down here

underneath the middle of the arch

so that as you're building it,

the blocks don't fall into the strait.

And that would require some scaffolding.

And this was just not acceptable to the admiralty at the time

because this is a very busy shipping channel

and they required 100 feet of clearance

above the high-water mark.

And that led telford to have to consider something

that could give him a very long clear-span

with no supports in the water even during construction.

Telford's solution

was the world's first major long-span suspension bridge.

For a suspension bridge, we need two very strong abutments,

and then you need two towers.

And then what you do is, once you've built your towers,

you take a cable like these guys,

and you string these up and over the towers.

And then you drop hanger cables down from the main cables

and then put your bridge deck in place.

And then once your bridge is completed,

if you have a load that comes along... say our car here...

It comes along,

and now when the load gets out near the middle of the span,

the load from the car then gets transferred up

through the hanger cables

into the main cable up over the tower.

The tension in that cable

gets anchored in these strong abutments,

and the compression force here

goes down into the foundations in the bedrock.

That's essentially how a suspension bridge works

like this beautiful bridge we have here.

Telford's suspended deck

was a stroke of engineering genius.

The key advantages of a suspension bridge

are that you can span long distances

with no supports below the bridge decks.

So you can get very long, clear, unsupported spans

because all of the support

is coming from the suspending cables

and the main cables up above you.

So below the bridge deck,

there's absolutely no obstructions,

which in a strait is obviously a very important thing.

A suspended bridge was the obvious solution

for Papanikolas and his fellow engineers

in the Gulf of Corinth,

but they would have to do it on a much larger scale.

The Rion-Antirion would need to be

an incredible seven times longer

than the Menai suspension bridge.

Unlike the main anchored cables of telford's suspension bridge,

this cable-stayed design would use individual cables

radiating from 4 huge pylons spaced 1,600 feet apart.

Each cable set would support a 40-foot section

of the bridge's deck.

In 2003, deck building begins.

Each section is floated out into the Gulf of Corinth

and attached to either side of a pylon until the decks meet.

This massive operation took more than a year to complete.

Just as they had to do for the bridge's pier footings,

designers had to ensure the deck could survive an earthquake

in one of the most active seismic zones in the world.

Expansion joints allow the deck to stretch

as the two land masses on either side slowly drift apart.

But protecting it against a massive earthquake

will require a groundbreaking new approach.

Instead of resting on the foundation piers,

the deck hangs just above

creating a single 1-1/2 mile long,

fully suspended floating deck.

When an earthquake strikes,

flexibility will be key to the bridge deck's survival.

The piers can move on their foundations.

And if the deck was attached when this happened,

it would buckle and break.

But it's also important that the deck doesn't sway

during the frequent high winds

experienced in the Gulf of Corinth.

Engineers had to ensure rigidity in normal conditions

but flexibility in the event of an earthquake.

Their solution... the world's biggest shock absorber.

If the bridge begins moving erratically,

a fuse breaks, sending the massive dampers into action.

This quake-busting design proved its worth

four years after the bridge opened

when a 6.4-scale earthquake hit the Rion-Antirion in 2008.

The innovative damping system kicked into action

saving the bridge from disaster.

But earthquakes aren't the only natural forces

that engineers will need to overcome.

To ensure the Rion-Antirion's survival,

they will need to take a look back

of some of history's great engineering catastrophes.

Designers of the almost 2-mile long

Rion-Antirion bridge faced huge environmental challenges.

In one of the most seismically active regions in Europe,

cutting-edge technology was developed

to protect the bridge from earthquakes.

But the bridge faces

another equally destructive environmental threat

that its engineers must overcome.

To protect this massive structure from wind,

engineers will need to take a lesson from the history books.

When the Tacoma narrow suspension bridge opened

near Seattle in July 1940,

it was thought to be at the forefront of bridge design.

But it wasn't long before the bridge

got the nickname "galloping gertie."

There was clearly a very big problem.

Just four months after opening,

the bridge's twisting motion became so violent,

it suffered a catastrophic failure...

...crashing almost 200 feet into the water below.

An investigation found

that the relatively light 40-mile-per-hour wind

was hitting the solid edges of the deck,

creating an unstable oscillation that fed off itself,

amplifying to the point of disaster.

The wind conditions are far more severe in the Gulf of Corinth.

The mountainous landscape creates a funnel,

where winds of 70 miles per hour are common.

The aerodynamics of the bridge deck are a crucial element.

The fairings safeguard the deck

from gusts of over 150 miles per hour,

but the massive cables holding up the deck

also need to be strong enough to survive extreme wind gusts.

The designers of the Rion-Antirion

looked to an engineering marvel created years ago

for the solution...

One that conquered a challenge once thought to be impossible.

In the second half of the 19th century,

the growth of New York City

was being stunted by the limits of the east river.

At that time, the only way for people

to cross from Brooklyn to Manhattan was by ferry.

You see here Manhattan to my left and Brooklyn to my right.

At the time, you could imagine just a river teeming with boats.

But in 1867, boat traffic ground to a halt.

A cold spell actually froze the east river over

and essentially halted commerce

because you could walk across the east river

at the time on the ice, but you couldn't actually trade.

So it was at that point when voices really kind of mounted

demanding a permanent kind of structural connection

between the two cities with a bridge

to have this lasting connection

so that you could have reliable transportation and trade.

The man given the job

was German-born engineer John Augustus Roebling,

and what he designed still inspires engineers today...

The Brooklyn bridge.

Just the concept of actually spanning

over such a long distance at such a height

was earth-shattering.

No bridge had been built even close to this span.

The Brooklyn bridge spans over a mile.

It was made possible by Roebling's use

of a revolutionary new material... Steel.

Just thinking of actually building

a bridge not of masonry

as we'd find in kind of traditional European style,

but saying, "we have this new material... steel..."

We will build the entire deck and the cables of steel."

This is an absolute engineering marvel.

Steel is stronger, lighter,

and more flexible than iron.

Roebling used this new material

for the bridge's four massive suspension cables.

He bundled hundreds of parallel steel wires together,

creating super-strong and super-safe cables.

Engineer Adrian Brugger

demonstrates just how much safer Roebling's design is

at Columbia university's engineering testing lab.

This cable is made up of actually independent

and small 5-millimeter circular wires.

In this case, there's 9,000 wires.

Those wires are then grouped into what we call strands.

You actually take those and you compact those into the cable.

This is kind of a huge leap from the technology we had before.

Because before what we had

was more or less serialized systems,

such as chains or these large I-bars.

Where if one of these I-bars failed,

then generally that meant that the entire bridge failed.

If one of these wires happens to be bad or has a crack in it,

then the entire cable still has 8,999 other intact wires.

Adrian compares the system used on the Brooklyn bridge

to those that came before it using a giant universal tester.

And more or less, a universal testing machine

just means that it's a machine that is built to crush things

and rip them apart.

First to be tested... A solid steel bar.

This would be very similar

to what you would have on an old bridge...

Pre-Brooklyn bridge for example.

The steel bar has been weakened at a specific point

and will be stretched under massive tension

to simulate a bridge failure.

So, we expect this bar to fail at around a good 200 tons.

Right now, you can see that the necking

is starting at about a quarter up from the reduced section,

so exactly where we wanted it.

And it'll become more and more pronounced

kind of as we see it now.

The energy release was massive,

and now the specimen has just catastrophically failed.

It's broken.

Such an explosive failure could result

in the collapse of a whole bridge

as tragically happened with Silver bridge in Ohio,

causing the loss of dozens of lives.

Next, Adrian tests Roebling's steel cable design.

As it's stretched, he subjects it to extreme heat

to weaken it simulating a fail.

So, we are seeing this cascading failure right now.

You can see each wire

is actually breaking one after another.

It's not just this one catastrophic failure

but rather this cascade.

When the cable starts to fail,

the remaining wires take up the load.

Even if all the wires fail,

the energy released is gradual rather than one huge explosion.

So, what you saw there was, you know, exactly why

the suspension bridge wires are such a great solution.

But you can see that you didn't have

this one catastrophic explosion and just failure of the member

but rather each one of these wires actually broke.

Steel technology enabled John Roebling

to design what was at the time the world's longest

and strongest bridge and an engineering masterpiece.

This bridge would eclipse

every other structure in the entire americas.

It would be the tallest structure anywhere.

So just a person actually standing on the tower

would be on essentially

the first skyscraper in the United States.

The designers of the Rion-Antirion bridge

will need to super-size the revolutionary ideas

of John Roebling and the Brooklyn bridge...

This type of oscillation

would be very worrying to the designers.

The structure could collapse due to oscillations such as this.

...And create even more impossible engineering.

180 feet above the Gulf of Corinth,

cutting-edge suspension technology

inspired by Brooklyn-bridge designer John Roebling

keeps the ultra-modern Rion-Antirion bridge

from crashing into the water.

But unlike New York City, near-hurricane force winds

are common in the Gulf of Corinth,

putting a great deal of stress on the cables.

At a wind-tunnel facility, professor Luke Bisby

demonstrates just how destructive wind can be.

All right, so, we're gonna start it up,

and we'll see what happens.

If this was a cable in a real bridge,

this type of oscillation

would be very worrying to the designers

because what this would mean

is that the metal that forms the cable

would be being stressed repeatedly back and forth.

And eventually in a metal cable, that can lead to fatigue,

which can cause cracking

and, hence, potentially failure of the structure.

So the structure could collapse

due to oscillations such as this.

When wind strikes a cylindrical structure

like a cable, it separates,

then rejoins on the other side,

causing the structure to oscillate...

A phenomenon known as vortex shedding.

Vortex shedding has been responsible for the collapse

of several chimneys and towers over the years.

In 1957, British scientist Christopher Kit Scruton

discovered that adding a simple fin to a cylindrical structure

would break up the wind vortices

reducing the vibrations that could lead to a collapse.

He called the fin a helical strake.

Just seeing a little bit of vibration here... not too much.

This is really incredible that this simple spiral

can completely prevent the motion

of this simulated bridge cable.

With the helical strake,

we get this disruption of the flow pattern,

we introduce some turbulence,

and both the formation of the vortices

and the vibration of the cable both stop.

The helical strake seems to be working.

Since >>>Kit Scruton invented the helical strake

back in the '50s and '60s,

it's been applied to tens of thousands of structures

and chimneys and Bridges around the world

and has really saved them from potential catastrophic collapse

due to wind effects.

Helical strakes are integrated

into all of the nearly 40 miles of cabling

on the Rion-Antirion bridge.

This, combined with spoiler-like deck fairings,

makes this bridge one of the safest on earth.

But a bridge can't just be functional...

It has to be beautiful.

So once again, engineers

will look to the innovations of the past for inspiration.

The Rion-Antirion bridge in Greece

is a wonder of the engineering world.

Its designers not only had to ensure

it could survive earthquakes and high winds,

but they were also forced to construct it

in extremely deep water on unstable soil.

Underwater, the bridge may be an enormous mass of concrete,

but above water, it has to be elegant

and add to the Greek landscape around it... not scar it.

Finding the right balance between strength and beauty

was quite a challenge for the engineering team...

A challenge that may have been insurmountable

had it not been for the great innovators of the past.

In 1928, renowned Swiss civil engineer Robert maillart

won a competition to design a bridge

that would link two remote towns

300 feet above the salgina valley in Switzerland.

The result... The salginatobel bridge.

Designated an international engineering landmark,

maillart's bridge proved to the world

that concrete could be both practical and beautiful.

Engineer urs meyer has been a lifelong fan

of the iconic structure,

but he's about to see it from an entirely new perspective.

Building a bridge in this remote part of eastern Switzerland

required great ingenuity.

Concrete is strong in compression,

but reinforcing it with steel bars

also gives it strength in tension,

allowing it to be manipulated into almost any shape.

Maillart designed an elegant three-pinned hollow box arch

supported by reinforced concrete columns.

This made the concrete strong enough

to transmit the bridge loads to the foundations

but flexible enough to absorb any ground movement

that could cause dangerous cracks to form.

Maillart's sleek design also used less reinforced concrete,

making it cheaper to build.

But there were some skeptics.

When the salginatobel bridge opened in August 1930,

it was hailed an engineering and artistic triumph,

proving to the world that concrete Bridges

could be both functional and beautiful.

1,000 miles away in Greece, maillart's influence can be seen

all over the Rion-Antirion bridge.

The four reinforced concrete pylons

embody cost-saving minimalism, flexible strength,

and elegant design.

780,000 tons of reinforced concrete ensure this bridge

could survive an earthquake of 7 on the Richter scale.

The Rion-Antirion bridge has redrawn the map of Greece,

and its designers have rewritten the rules

of bridge engineering forever.

By modernizing innovations of the past

and making groundbreaking discoveries of their own,

the engineers and designers of this incredible structure

have succeeded in making the impossible possible.

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