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ANNOUNCER: This program is rated PG, and contains

ANNOUNCER: This program is rated PG, and contains

mature subject matter.

Viewer discretion is advised.

(OPERATOR SPEAKING ITALIAN)

(MAN SPEAKING)

NARRATOR: It's the deadliest bridge disaster in Italy's history.

It's no longer a bridge. It's just a collection of concrete chunks raining down.

But why did it collapse?

Was it corrosion? Was it an impact? What was the reason for it?

Now...

engineers unlock the clues to the world's biggest disasters...

to find out what happens When Big Things Go Wrong.

Watch it, watch it

These are the ultimate fears that keep engineers awake at night.

MAN: Oh, my god.

11:30 on a stormy Tuesday morning in Italy's largest port city.

Genoa is kind of famous for these strong thunderstorms like water bombs.

So that morning was one of those mornings.

Travelers are warned to stay indoors.

But Genoa's major highway, the E80, is filling up with traffic.

Among the drivers, off-duty firefighter, Davide Capello.

(SPEAKING ITALIAN)

Davide joins the hundreds of cars crammed on the E-80.

The E80 is also known as the Trans-European motorway,

because it connects ten countries over 3,000 miles of highway.

Spanning a key link: one of Europe's longest bridges

named for its designer, Riccardo Morandi.

The Morandi Bridge was really ahead of its time.

He was trying materials and methods that weren't used up to that point,

so he was trying to advance the state of the art.

The bridge is among the world's longest, the length of 13 football fields.

It's what's called a "cable-stayed" bridge.

The striking design features a deck supported by cables.

They're wrapped in concrete and hang from massive 300-foot-high piers.

For me it was always like, "Oh, look at this masterpiece,"

look at this piece of engineering rising across this valley.

Because it was a very imposing severe structure,

sometimes it was also menacing.

What nobody knows, is the bridge is in trouble.

On this dark and stormy morning,

every vehicle crossing it brings it closer to collapse.

Davide Capello is one of many drivers approaching the bridge.

(TICKING)

(TICKING)

In front of him, a slow-moving lane of cars.

Davide drives onto the bridge deck, 150 feet above the city.

(DAVIDE SPEAKING)

For Davide, and many other drivers, time is up.

(TICKING)

A massive 690-foot section collapses...

taking over 30 vehicles with it.

It's no longer a bridge, it's just a collection of concrete chunks

raining down on the apartment buildings in the city below

as well as carrying cars from on top of the bridge down into this hellish

scape of debris and destruction.

It's the worst engineering disaster in Italy's history.

As emergency services search for the injured and dead,

everyone wants to know why the bridge collapsed.

I remember going on the scene and there's this huge gap.

And and you're kind of left thinking, "What happened?"

The first reaction was, loss of life, hurt people.

The second one is the engineering side of it.

Was it corrosion, was it impact? What was the reason for it?

Those were the questions that were going on in our minds.

How could a bridge that has stood for over 50 years be gone in seconds?

The answers to this mystery begin before the bridge was even built, in 1958.

Italy's economy is booming.

But its roads are in dire need of modernization.

So a brand new network of highways is being built,

including one to the port city of Genoa.

Genoa is a crazy city. It's squeezed between the ocean and the mountains.

There's very few east-west roads,

so you would get stuck.

To cross the ancient city, a mile-long bridge is needed.

But building it won't be easy.

MATTIOLI: We have residential condominiums,

a big railyard, we have industries

so we need an engineer that can think of a bridge

that can skip above these different things.

In 1962, a call goes out to the world's greatest architects

including Riccardo Morandi.

Morandi was was revered within the Italian engineering community

as something of an engineering genius.

He was designing and constructing bridges and conceiving bridges

and bridge designs that were very different from what was standard at the time.

Famous for his lighter and thinner bridges,

Morandi picks a cable-stayed design.

(MORANDI SPEAKING)

But Morandi's plan comes with a big problem...

a design flaw that's the first clue to the bridge collapse.

His decision will contribute to a disaster 50 years from now.

A cable-stayed bridge features multiple thick cables supporting the deck and traffic below.

On designs like the Brooklyn Bridge,

the load is spread across tens or even hundreds of cables.

But Morandi relies on just four cable stays coming down from each pier.

When he designed the bridge, many thought that the four cable stays per pier

were state of the art.

It's a big risk.

There's not that much stuff there to keep the bridge up,

which is pleasing to the eye,

but it's a balance between looking good and staying upright.

Morandi takes the gamble.

The minimal design may look elegant,

but using fewer cables comes with a crucial weakness.

The problem with having a cable-stayed bridge with only four cables

is if just one of those cables fails, the entire structure is compromised.

Ultimately, it's bad news.

Flaw design on big projects carries big risks...

a lesson learned the hard way at another infamous bridge.

Washington State's Tacoma Narrows Bridge.

At 2,800 feet long, this structure was

the third-longest suspension bridge in the world.

Opened in 1940, it's a marvel of modern engineering.

And just like the Morandi Bridge, it has a design flaw,

one revealed on a windy winter's day.

One day in early November, the bridge is twisting up to 28 feet

and at angles of 45 degrees.

Stuck on the bridge is Leonard Coatsworth, a local news editor,

forced to abandon his car.

He's heard a cracking noise

and is desperately trying to get to safety.

So what led to its unexpected collapse?

Like the Morandi, the Tacoma Bridge has a minimalist design.

The structure holding up the bridge deck is thinner than usual.

Traditional designs have a thick central truss,

but here it's a girder just eight feet wide.

The bridge deck didn't have a large metal stiffening truss underneath it.

Instead, the bridge deck was held up on long girders that ran along the sides of the bridge.

The result is a bridge that looks thin and elegant.

But there's a fatal weakness. It's too flexible.

The bridge even gets a nickname. Galloping Gertie.

The wind was sufficient to excite the bridge and ultimately shake it apart.

It lasts just four months.

The breaking point, when wind speeds surpass 40 miles per hour.

But Morandi's bridge stands for over five decades.

So what else can explain its disastrous collapse?

Coming up...

More clues uncovered.

When you incorporate a new design and a new material,

those risks don't just add, they multiply.

And later, more shocking disasters When Big Things Go Wrong.

When big things go wrong, engineers need to figure out why.

In the collapse of Italy's Morandi Bridge,

the first clue is its flawed design.

But the bridge doesn't fall down right away.

So what else goes wrong?

In the aftermath of this bridge's collapse

there is a lot of anxiety.

The question on everyone's mind is "Why did this happen?

"Why did this go wrong?"

Morandi's daring decision to use pre-stressed concrete could spell disaster.

But how?

As the bridge is built,

the steel cables that will hold up the road are put in place.

These need protection from the elements.

Normally in a cable-stayed bridge,

the stay cable would be encased within some kind of skin made out of metal, say steel.

But Morandi tries something else.

There's a new material at the time,

pre-stressed concrete, which was a revolution

for the era in the 1960s that allowed bridges to be built

that were much more slender and more beautiful.

Morandi decides to wrap each of the steel cables in pre-stressed concrete.

Rarely would you see a stay cable encased within pre-stressed concrete.

This new material was something that wouldn't have been used that many times at this scale.

But Morandi and his engineers think it can work.

A beam made from ordinary concrete is brittle and breaks easily under stress.

Pre-stressed concrete contains steel wire pulled tight.

They squeeze and compress the concrete for extra strength.

ASEGUN HENRY: So it's a rather clever idea, right?

The idea that the concrete itself is very strong when it's in compression.

Its ability to resist bending is actually better.

You get more strength out of it.

Morandi also thinks concrete will protect the cables over time.

He races ahead. And in 1967 his daring bridge opens to excited crowds.

This bridge is so sound, it's so robust,

it's so efficient and technologically-advanced

that it basically will never need maintenance.

At least, that's the idea.

There's always a risk when you're trying out brand new designs and techniques.

But it's only when you build it that you really know if it works.

It's a risk a wedding party in Jerusalem tragically discover.

Versailles Hall. Jerusalem.

Seven hundred guests celebrate the marriage of Keren and Asaf Dror.

The ceremony took place earlier that day.

Now the couple are partying with close friends and family.

It's a wedding. Everybody's having a good time out on the dance floor.

Then all of a sudden...

(SCREAMING, COLLAPSING)

It's hard to imagine observing something quite so horrific going from joy to tragedy

in such a short space of time.

BELL: Half the building has collapsed.

Twenty-three dead, 356 injured.

It's the most lethal civil disaster in Israel's history.

It was so bad that an investigation was launched to find out

if this was the result of a terrorist attack.

The truth was much simpler.

What they found was concrete was to blame.

Just like the Morandi Bridge,

Versailles Hall is built using a new type of concrete.

It's thinner than usual and known for its strength and durability.

But this concrete floor doesn't support the weight of a wedding celebration.

When you have people dancing in rhythm with the music, and in rhythm with each other,

that's gonna induce a load on the structure

that would have been simply too much for this weakened, overweight structure to handle.

More than 350 people, including the newlyweds, fall through two floors.

The groom survives, and carries his bride from the rubble, injured but alive.

This particular concrete was just a recipe for failure from the start.

The lesson for the Morandi Bridge disaster,

untried materials can bring unintended consequences.

But how did this new concrete trigger the collapse?

In Italy, the collapse of the Morandi Bridge shocks the world.

MATTIOLI: How do we go from building one of the most extraordinary structures

in the world to a sudden collapse

that nobody even anticipated?

Time for the next clue.

HERRMANN: Morandi tried to prepare for the future,

and his thoughts were that

the steel cables compressing the concrete would keep the concrete from cracking.

And then concrete encasement around the steels would protect the steel from the environment.

In principle, that's a good idea because pre-stressed concrete shouldn't crack.

The challenge is, that if it does crack,

you can't see hidden deterioration within your structure.

And the inability to inspect the condition of the stay cables in particular,

that was one of the big faults that Morandi made in designing this bridge.

Another problem, the bridge's location.

It's located less than one kilometer from the ocean,

so you have all this sea salt air, this ocean air.

The positioning of the Ponti Morandi Bridge was almost the worst-case scenario

because salt water is extremely corrosive.

Plus you have a lot of factories which increase to the pollution and they mix

with the salty air from the ocean,

and the bridge is immersed in this atmosphere for a long time.

In 1979, cracks begin appearing on the towers and even on the stays.

Morandi himself raises the alarm.

Morandi goes back on the bridge and starts realizing that there are

some problems with the concrete.

What he found was the effects of the saltwater mist,

and also all the factories under the bridge

with the industrial pollution, were combining to rapidly

decompose the materials on the bridge itself.

To try to stop the decay,

Morandi issues orders to concrete over the cracks.

I mean, he's not saying that the bridge is structurally compromised.

He's just saying, you know, the concrete needed intervention.

But hidden within the bridge's concrete stays,

the corrosion runs far deeper than Morandi imagines.

Salt and pollution have crept in and are eating into the critical steel support cables.

Over time, up to 30% of the metal inside each of the stays disintegrates.

Work to seal up the cracks is finally completed in 1985.

But the repair just makes things worse.

Normally, if you just had exposed metal,

the water would just evaporate off when it warms up.

All this concrete actually prevents the water from being able to get back out

so it can start eating away at the metal over time.

The crucial components supporting the entire weight of the bridge

are concealed and failing.

That same flaw will doom a Philippines high-rise in 2004.

The crowded megacity of Manila.

An unseen problem brings an eight-story tower crashing down.

As a structural engineer, it's really surprising.

This is the kind of thing that we just don't see.

There is something about the foundation of this building

that has gone really horribly wrong.

Just like the Morandi Bridge, there is unseen danger lurking inside its structure.

For the past five years,

weaknesses have slowly developed deep in the tower's foundations.

When you build a building, you have to be concerned with the quality of the ground

that you're building it on, not all dirt is the same.

Some dirt has a tendency when it rains to become mud-like.

There is an entire group of engineering professionals called geotechnical engineers

whose job it is to understand the sub-surface conditions in the foundations of buildings.

Occasionally, geotechnical engineers get it wrong.

Before it falls, this tower gives a warning.

A loud crack rings out as it starts to tilt.

Occupants scramble to safety, and the authorities close the busy road.

Just in time.

Just like the tower block in the Philippines,

the Morandi Bridge in Italy is heading for disaster.

But there's still a chance, if clues are seen, the catastrophe can be avoided.

Coming up...

Will engineers finally spot a key warning sign?

Everyone's like, "Hold on one second, how is it possible?"

And poor maintenance makes a deadly outcome inevitable.

That water wants to get out of that dam.

When big things go wrong,

there's always a reason why.

In Italy, engineers continue searching for the cause of the Morandi Bridge collapse.

Some things are clear. The bridge's design is flawed.

DICKRELL: If one of those cables fails,

there's really not much room for error for the rest of the cables to take up the load.

The new wonder material used to build it has a weakness.

We now know that concrete has its limitations.

But what else accounts for the bridge collapse?

MATTIOLI: I think this story is not just about a failed design,

I think this story is about an incredible design,

that everybody who came after failed to maintain.

Morandi personally carries out inspections.

But after he dies in 1989, there are no more for the next three years.

Finally, in 1992,

engineers focus on the three towers that hold up piers 9, 10 and 11.

MATTIOLI: There were inspectors going up tower number 11,

and they see on the top of the tower

that all the stayed cable that were supposed to be imbued in concrete

are corroded, that they're not supposed to look this way.

Huge red flag, right? Because this is the crux of the whole design.

As that corrosion starts to happen, those steel cables become a liability.

So if the metal snaps, you lose that ability to stress the concrete

and all of a sudden the concrete becomes much weaker and it'll snap.

They decide to repair the exterior of pier 11.

MATTIOLI: They managed to reinforce the tower by adding more cable on the outside.

They look into tower number 10 and tower number 9.

But they don't really see nothing wrong with them.

So, one tower is totally compromised.

and you decide to intervene right away.

And then the other two are fine?

After repairs to pier 11 are completed in 1994,

no other major repairs take place for 24 years.

MATTIOLI: All the people saying it looked fine, it looked fine.

I don't think anybody feared that the bridge would fall down.

When a big structure is already compromised, a lack of upkeep can be deadly,

as a dam disaster in Brazil dramatically proves.

A busy mine in the south-east of the country.

Hundreds of workers extract 20,000 tons of iron ore per day.

The mine also produces billions of gallons of liquid waste

stored behind a 400-foot dam.

And like the Morandi Bridge, maintenance here rarely takes place.

On January 25th, 2019, the dam collapses.

Two hundred seventy die.

The Brumadinho Dam is an example of what not to do in a large-scale engineering project.

From the outset, this structure is doomed.

The Brumadinho Dam is what's called an upstream dam.

Unlike a normal dam that's fully constructed before it's filled with water,

an upstream dam is built as it's filled.

Most large modern dams are made of concrete,

but this one's made of earth, waste from the mine itself.

And as the mine grows, so does the dam.

You are essentially building a dam on a dam on a dam, on a dam.

And building the dam ever higher.

And putting ever more material behind the dam.

An inspection shows pressure is building.

That water wants to get out of that dam,

so it's exerting a great deal of force on that dam,

which is not particularly well-constructed.

When it's already too late, a team is sent out to drill holes

and relieve some of the pressure.

But it bursts, sweeping workers to their deaths.

So if these boreholes had been created earlier before the entire structure of the dam

was saturated with water, then maybe the failure could have been prevented.

Coming up...

More shocking disasters When Big Things Go Wrong.

After standing tall for over 50 years,

the Morandi Bridge in Italy collapses suddenly with a massive loss of life.

What sends it over the edge?

Hidden below its surface, invisible to the thousands of people crossing it every day

are clues to its demise.

However, one obvious warning sign was missed right from the start.

Another bridge built by Morandi in Venezuela is strikingly similar to his design in Italy.

DICKRELL: That bridge was very well regarded

so much so that it helped him win the bid

to basically duplicate the same style of bridge in Italy.

But the Venezuelan bridge is not as strong as it looks.

NEWSCASTER: A 1,500-foot section of this five-mile concrete bridge

was ripped out by an oil tanker

that got out of control in Lake Maracaibo, Venezuela.

The accident reveals the fatal flaw in Morandi's design.

The tanker only had to take out one leg to start a chain reaction,

and an 850-foot-long section of deck has come crashing down into the lake below.

The Italian bridge could have the same problem.

But astonishingly, Morandi makes no attempt to change it.

He's ignoring the warnings from his own bridge in Venezuela.

The Venezuela bridge lasts

lasts just two years before its weakness is exposed.

The Morandi Bridge stands for five decades.

But its hour of reckoning is near.

What tips it over the edge?

DICKRELL: This bridge is in trouble.

It's gonna fail, it's just a matter of when.

(TICKING)

Davide Cappello leaves his girlfriend's home

and jumps on the highway on his way to Genoa.

(DAVIDE SPEAKING)

MATTIOLI: The thing that everybody remembers very clearly is how

dark everything got by 11:00 a.m. because of this thunderstorm.

(THUNDER RUMBLING)

A sign of impending doom goes unnoticed.

BELL: You'd be forgiven for looking at this footage and thinking, "So what?"

Look again.

Pier 11 is surrounded by re-enforcement

just like it has been for the last 25 years.

Pier 10, nothing strange

Pier 9, stop there.

Do you see that there? That is an enormous crack.

When we see a crack that's the width of a coin,

we tend to get worried in a reinforced concrete structure.

It's telling us that the structure is in significant distress.

This huge crack suggests the bridge could be minutes from failing.

One more car or truck could be the final straw.

(TICKING)

As rain pours down, the last few cars drive onto the bridge.

(TICKING)

At 11:36am... time is up.

(TICKING)

-BELL: There's a loud crack, -(EXPLOSION)

and it appears that one of the main stays

that hold the road deck in place snaps.

(DAVIDE SPEAKING)

DICKRELL: It's no longer a bridge, it's just a collection of concrete chunks

raining down on the apartment buildings of the city below.

You immediately think of how many cars are on it.

In just 17 seconds, a 690-foot section of bridge has smashed into the city below.

(OPERATOR SPEAKING)

(MAN SPEAKING)

Over 30 cars plummet into the void,

one of them containing Davide Capello.

Emergency services scramble to vehicles suspended in the ruins of the bridge.

Some drivers are rescued quickly, but Davide remains trapped.

(MAN SPEAKING ITALIAN)

Davide has fallen nine stories,

further than he or anyone could imagine.

His SUV stuck inside a crater in the collapsed wreckage.

(HELICOPTER WHIRRING)

Davide finally crawls out the rear window,

miraculously unscathed.

The collapse doesn't just shock Italy, it shocks the world.

Forty-three are dead, 16 seriously injured,

600 homeless.

A state of emergency is declared,

as investigators search the rubble looking for answers.

Italy has just suffered

one of the worst engineering disasters in its history.

A 690-foot section of the Morandi Bridge has collapsed.

Dozens are dead and hundreds of people evacuate the area.

The city is in shock at a collapse that seemed to come out of nowhere.

But look through the eyes of an engineer, and the clues are all there.

A fatally-flawed design.

With just four main members holding up

the weight of that bridge, it's rather surprising it lasted for so long.

Untested new materials.

Rarely would you see a stay cable encased in pre-stressed concrete,

and that's what Morandi chose to do.

Hidden dangers.

The concrete slowly cracking,

the steel cables buried inside are rusting away.

And a missed warning.

This bridge was doomed from the start.

(TICKING)

On a rainy August morning,

it can no longer support its own weight.

The collapse starts when corroded steel cables inside pier 9 finally snap.

(MAN SCREAMING)

Highly-tensioned steel gives way, like an elastic band breaking.

HENRY: Now the entire bridge in unbalanced, the weight transfers immediately.

As soon as it transfers, the next one breaks.

DICKRELL: As the support s break away the structural integrity

of the Ponte Morandi Bridge is lost.

BISBY: The forces from that are transferred back to the tower,

and you have this domino-ing failure of the rest of the structure.

(EXPLOSION)

The collapse takes just 17 seconds...

crushing cars and warehouses...

destroying Railway lines...

killing 43.

It's a day no one in the world will forget.

MATTIOLI: Imagine a structure that you

associate with something that is robust and solid,

and then all of a sudden coming down like that is definitely

shocking.

(DAVIDE SPEAKING)