All language subtitles for When.Big.Things.Go.Wrong.S01E03.Overloaded.1080p.AMZN.WEB-DL.DDP5.1.H.264-BurCyg_track3_[eng]

ANNOUNCER: This program is
rated PG, and contains

ANNOUNCER: This program is
rated PG, and contains

ANNOUNCER: This program is
rated PG, and contains

mature subject matter.

Viewer discretion is advised.

(DRAMATIC MUSIC PLAYING)

(HELICOPTER BLADES WHIRRING)

(SIRENS WAILING)

(WOMAN SPEAKING)

(MAN SPEAKING)

NARRATOR: It's one of
the deadliest bridge collapses
in history...

It looks like something
out of a disaster movie.

NARRATOR: But why did it fail?

Was it terrorism?

Was it heavy loads?

Was it corrosion?

NARRATOR: Now...

(CAPTIVATING
INSTRUMENTAL MUSIC PLAYING)

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

(TRAIN HORN BLOWING)

(WOMAN SCREAMING)

...to find out what happens
When Big Things Go Wrong.

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

(PEOPLE SCREAMING)

MAN: Oh, my God!

(SUSPENSEFUL MUSIC PLAYING)

NARRATOR: It's 6:01
in Minneapolis

on a scorching hot
summer afternoon.

Crossing the I-35 bridge
is an everyday commute
for thousands of drivers,

like Lindsay Walz.

I had the air condition
full blast,

my windows were up

so that I could stay
as cool as possible.

NARRATOR: Approaching
from the other direction,

businessman Andy Gannon.

I grew up in South Minneapolis,
probably about five miles away
from the 35W bridge.

I crossed it, on average
during the week,
about four or five times.

I knew the bridge
was going to be busy

because that's considered
rush hour in Minneapolis
at that time of day.

It's probably the worst time
to be driving in
downtown Minneapolis.

(DRAMATIC MUSIC PLAYING)

NARRATOR: The I-35 bridge

runs north-south across
the Mississippi.

Opened in 1967, it's one of
the busiest in Minnesota.

JOHN LAURITSEN:
It's a workhorse bridge.

It's a bridge that gets you
to and from where
you need to be.

And it is something that
you wouldn't think twice
when you drive on it.

You wouldn't
think about it at all.

(SUSPENSEFUL MUSIC PLAYING)

ROB BELL: Most people
don't think of this bridge
as special at all.

But 140,000 cars and trucks
drive cross it every day.

That's more than
the Golden Gate Bridge.

NARRATOR: A workhorse
built for punishment,

the I-35 is a truss bridge.

Made of steel beams
joined together

to form two large trusses
resting on four concrete piers.

It's a strong,
load-bearing bridge

that carries eight lanes
of interstate traffic.

What nobody knows is that
the bridge is fatally weakened

and each extra car
is taking it closer
to catastrophic collapse.

(CLOCK TICKING)

I am creeping forward, just,

like, car length
by car length.

I wasn't even putting
my foot on the pedal,
you know, to put the gas on.

It was just un-brake
and re-brake.

I got to probably about
the middle of the bridge

and there was a really loud

clank.

(EERIE MUSIC PLAYING)

I can hear the...
The actual sounds of failure,

mechanical failure, loud,
you know, cracks and breaks.

I'm thinking, "This isn't good.

"I've got to get
off the bridge."

NARRATOR: But time runs out
for the drivers on the bridge.

(CLOCK TICKING)

The bridge collapses,
taking 111 vehicles with it.

It's as though someone has just
kicked the legs out from a table

and the whole thing
just drops down into
the river below.

Over 10,000 tons of steel
and 1,000 feet of bridge

come crashing down
into the water.

You are waiting for this...
This monster,

this wave of concrete
to come and take your life.

(POLICE SIRENS WAILING)

Because my car was nosediving,

the water just came up
through the engine,

and through
the ventilation system,

and right up into
the cabin of my car.

So, by the time
the car actually, like,

settled and stopped moving,
I was drowning.

(THRILLING MUSIC PLAYING)

I thought that was it. For sure.

(SIRENS WAILING)

(HELICOPTER BLADES WHIRRING)

(DRAMATIC MUSIC PLAYING)

NARRATOR: Shocked
by multiple casualties,

Minneapolis confronts one of
the deadliest bridge collapses
in U.S. history.

It looks like something
out of a disaster movie.

NARRATOR: But what caused it?
And how?

ANDREW HERRMANN:
Was it terrorism?
Was it heavy loads?

Was it corrosion?

You just have
all these questions

that you want to try to answer
to find out why it actually
did come down.

NARRATOR: The answers to
this mystery could lie in

decisions from before
the bridge was even built.

And the trail of clues
starts in 1956,
in the nation's capital.

(DRAMATIC MUSIC PLAYING)

With the Cold War at its peak,
President Eisenhower embarks

on one of the biggest
engineering projects in history,

building the interstate
highway.

The plan is to build
48,000 miles of road

so that cities can be
quickly evacuated

if the Russians
drop an atom bomb.

(EXPLOSION)

And so he sets out on this
very ambitious campaign
to build a system of highways.

NARRATOR FROM ARCHIVE:
Chicago, Dallas,
Baltimore, Miami.

An efficient system of highways
and interstate freeways.

You've got a lot of rivers,
you've got a lot of valleys,

you've got a lot of mountains,
and they all have to be crossed,

and that can't all be done
just with highway.

You need bridges
that close the lengths.

If you want to
build a strong bridge
and over a big obstacle,

the go-to design
is the truss bridge.

Truss bridges are
some of the most simple
bridges to build.

An ideal situation
when it comes to

putting up a lot of bridges
in a short amount of time.

NARRATOR: They seem
the perfect choice

for Eisenhower's
enormous network.

But they come
with a big problem.

A design flaw
that's the first clue
to the I-35 disaster.

By 1964, it's Minneapolis'
turn to join

one of the longest
highway networks in the world.

But first, engineers
must build a bridge

across the mighty
Mississippi River.

(SURREAL MUSIC PLAYING)

They choose a truss design.

A framework
of steel beams and posts

arranged in a series
of triangles.

Triangles are very stable
structural shapes.

What they do is,

they take triangles

and they bolt them together

as they try to bridge
the span.

BISBY: One of the reasons
a truss bridge
makes sense here,

is it's a very rigid
type of bridge.

So, if you're carrying
very heavy traffic loads,
four lanes of traffic,

you don't want your bridge
moving down too much
under those loads.

And a truss bridge is
a very rigid structural form.

NARRATOR: But for
all its strength,

this design has
a crucial weakness.

Most bridges can support
the loss of one key part,

but not a bridge like this.

HERRMANN: When you're
using a truss,

you generally only have
two trusses crossing the river.

So if one fails,
the entire bridge
will potentially collapse.

NARRATOR: In a perfect world,
the I-35 would be built

with a safety feature
called redundancy,

where if one truss breaks,
there are backup supports
in between to prevent collapse.

But the I-35 doesn't have that.

It only has two trusses.

And if either of them fails,

the entire bridge
will be destroyed.

BISBY: If you fracture
one piece of the bridge,

the whole structure comes down
like a house of cards.

NARRATOR: A big structure
without a backup plan
is a huge risk.

A lesson learned
the hard way in Florida.

(DRAMATIC MUSIC PLAYING)

Miami.

A new pedestrian bridge
has just been built to connect
a college campus to town.

It's only been
standing for five days,
when disaster strikes.

Just like the I-35 bridge,
the collapse is instant
and shocking.

But that's not
the only similarity.

Because a clue
to the destruction
of the Miami bridge

is in its design.

The designers want to
wow people with this bridge,

so it's got an asymmetric
zig-zag pattern,

which gives it
an interesting look,

but at heart,
it's a truss bridge
with triangular sections,

just like the I-35.

NARRATOR: But it's built
with just one truss.

If this fails,
the bridge is in danger.

It's being constructed
on the side of the road
in one piece,

and then, in an overnight lift,
will be brought up,

put in place and set down.

One day, you have no bridge,

the next day, there's
a pedestrian bridge present.

NARRATOR: From
the moment it's up,

the bridge is in trouble
and starts cracking.

(EERIE MUSIC PLAYING)

Now, for concrete bridges,
a certain amount of cracking
is not that worrisome,

but these cracks
were much, much larger.

NARRATOR: Five days later,

workers are sent in
to carry out emergency repairs.

But it's too late.

(DRAMATIC MUSIC PLAYING)

(HORNS HONKING)

(SIREN BLARING)

(WOMEN TALKING)

NARRATOR: The collapse starts
when a diagonal beam breaks,

and with no backup,
the entire bridge follows
like a house of cards.

Six die,
including one worker.

Like the Miami bridge,

the I-35 bridge in Minneapolis
has a flawed design.

And the scary truth is,
there 18,000 other bridges
in the U.S. built the same way

with no backup.

But they're not falling down.

So there must be other reasons

for the mysterious collapse
in Minneapolis.

Coming up...

More clues uncovered.

BELL: Unknown to anybody,
not the designers,

not the builders,
a mistake has been made.

NARRATOR: And a Milwaukee
mega crane shows
what can happen

when big things get
overloaded.

(DRAMATIC MUSIC PLAYING)

(CAPTIVATING
INSTRUMENTAL MUSIC PLAYING)

(DRAMATIC MUSIC PLAYING)

NARRATOR: When big things
go wrong,

engineers have
to find out why.

MAN: (ON RADIO)
I have serious doubts
about making the airport.

(PEOPLE SCREAMING)

NARRATOR: In the case
of the I-35 bridge
in Minneapolis...

The first clue
is its flawed design.

But there are thousands
of bridges just like this,

and they're still standing.

So what else
explains this failure?

More answers may lie
in its construction

and a deadly error
in a crucial component.

1967, and the bridge
is taking shape.

Engineers think
they're building it
strong enough to ensure

it never fails,
whatever it faces.

When engineers design things,

they incorporate something
called the factor of safety.

Basically, a truss bridge
like I-35 is made twice
as strong as it needs to be.

NARRATOR:
The key to that strength,

flat plates of steel
called gusset plates.

So the function of
a gusset plate is to glue

the members of
the truss bridge together.

NARRATOR: These
crucial components

join all of the steel beams
on the bridge together.

They attach at the ends of
each triangle along the truss,

with bolts and rivets
on both sides

to create a very
strong joint.

And there are 56 of these
joints

on both east and west
sides of the bridge.

As the last steel plates
are riveted on,

the I-35 bridge opens.

Here we go.

(PEOPLE CHEERING)

NARRATOR: But there's a problem.

Unknown to anybody,
not the designers,
not the builders,

not the first people
driving over the bridge,

a mistake has been made.

NARRATOR: The engineers
miscalculate the size
of 24 of the key plates

holding the bridge together.

BISBY: And some
of the gusset plates

that are in critical locations
in this structure

are about half as thick
as they ought to be.

NARRATOR: They should be
one inch thick.

Instead, they're half inch.

This compromises the bridge

because they're holding together
critical members of the truss.

And if one of the joints fails,
the entire bridge has
the potential for collapse.

NARRATOR: It's incredible.

The structural integrity
of a huge bridge

weakened by
24 small steel plates
that are simply too thin.

But a small part
can bring down a big thing,

as construction workers
in Wisconsin discover.

(DRAMATIC MUSIC PLAYING)

In Milwaukee,
the Brewers' baseball stadium
is getting an upgrade,

a new roof.

We're gonna have
a roof on next year.

Whoo!

The roof is created
with steel sections

that are a million pounds each.
Heavier than a 747.

NARRATOR: This huge job
requires a mega crane
with a fitting name.

Big Blue.

But as it lifts the roof,
there's a sickening crack.

(METALLIC CREAKING)

MAN: What the hell is that?

Watch it! Watch it!

NARRATOR: The clue
to Big Blue's destruction

lies in the failure
of a single, small part.

Just like the I-35 bridge,

Big Blue relies
on a key component

to hold its
mighty frame together.

The kingpin.

A foot wide and 11 feet long,

it's 1/50th the size

of the massive lifting arm
it holds in place.

The kingpin is strong,
but not unbreakable.

The crane is designed
to be used in winds
under 20 miles per hour,

and on this day,
the winds were at
26 miles per hour and more.

The load can act
like a big sail or a wing.

NARRATOR: As it lifts the roof,
that cracking sound...

(LOUD CRACK)

...is the kingpin breaking.

MAN 1: What the hell was that?

MAN 2: What's going on here?

NARRATOR: With the crane arm
acting as a massive crowbar,

the force on the kingpin
builds up until it ruptures,

shattering the huge washers
that hold it in place

and snapping off the end.

It's a fatal failure
for Big Blue.

(LOUD CRACK)

MAN: Watch it!
Watch it! Watch it!

(DRAMATIC MUSIC PLAYING)

NARRATOR: One small piece,
one giant disaster.

The lesson for
the I-35 bridge,

big things are only as strong
as their smallest parts.

And in Minneapolis,
some of these are
too weak to do their job.

But what caused
them to break?

(GENTLE
INSTRUMENTAL MUSIC PLAYING)

(GENTLE
INSTRUMENTAL MUSIC PLAYING)

(DRAMATIC MUSIC PLAYING)

NARRATOR: In Minneapolis,

unraveling clues
to the I-35 disaster
is an engineer's top priority.

You just have
all these questions

that you want to try
to answer to find out

why it actually did come down.

NARRATOR: And for the victims,
a terrifying ordeal.

I can hear the cracks and breaks

and I'm looking out
and I see the bridge
actually drop.

I thought I was going to
die a bloody mess.

NARRATOR: Despite
a flawed design
and a dangerous mistake,

the I-35 bridge
still stands for 40 years.

So what else explains
its sudden collapse?

The next clue lies
on top of the bridge.

1977. The bridge has
been open for a decade.

In that time, traffic across
the interstate system doubles.

Bad news for the already
compromised I-35 bridge.

Traffic over the bridge
has increased dramatically
since it opened,

increasing the load
it regularly has to take.

NARRATOR: And it's not
just cars.

Every 18-wheeler causes
as much road damage
as 9,000 cars.

But increased traffic
isn't the only extra weight
on the bridge.

So in 1977, the roadway
of the bridge was deteriorating.

And it was decided that
a new concrete surface

would be added
to extend its life.

Over the entire length
of the bridge,

this added three million pounds
of additional weight.

NARRATOR: That's not all.

Over the next 20 years,

extreme weather
puts even more stress
on the already strained bridge.

(SIREN WAILING)

REPORTER: On 35W and St. Paul,
a school bus and car collided.

No one was injured.

The I-35 bridge
has a problem with black ice.

It's so close to the Falls,
that mist is coming over

and with the extreme conditions
in Minnesota, it freezes.

So, they put this
de-icing system on the bridge

to combat that
and make it safer.

But this adds over
1.2 million pounds
of additional weight.

Three million pounds
thanks to the new
decking system,

and 1.2 million pounds
due to the de-icing system.

None of that additional weight
will have been considered

by the bridge's
original designers.

NARRATOR: A big structure
compromised by bad weather.

It's a recipe for disaster,
as horrified music fans
learn in Indiana.

(CROWD CHEERING)

12,000 fans
are gathered to watch
country duo Sugarland...

Just as a storm rolls in.

(PEOPLE SCREAMING)

How did a grandstand
that's been used
countless times before

collapse,
killing seven people?

(FIRST RESPONDER
SPEAKING ON RADIO)

(SUSPENSEFUL MUSIC PLAYING)

NARRATOR: Like the I-35 bridge,

this structure's
built with trusses.

And also,

like the I-35 bridge,

it doesn't take much
to overload it.

BISBY: Now what's
important to understand

about a tent structure
like this grandstand

is that the posts
that hold the roof up
need to stay vertical

and the design is intended
to make sure that that's true.

NARRATOR: The posts
are tied to concrete blocks

with steel wires
to keep them upright.

Each block is heavy.
Four thousand pounds.

So the structure can
withstand winds as high
as 43 miles per hour.

But increase the wind by just
another 15 miles per hour,

and the extra load on the posts
is enough to bring them down.

(PEOPLE SCREAMING)

As a result,
seven people are killed.

Just like the stage
in Indiana,

the I-35 bridge in Minneapolis
is heading for disaster.

But it's not there yet.

There's still a chance.

If clues are spotted,

catastrophe can be avoided.

(FAST-PACED MUSIC PLAYING)

Coming up...

WALZ: Who was that?

Who took a picture
of that bent gusset plate?

NARRATOR: Will engineers
spot a critical warning?

All this bridge needs
is one extra nudge.

NARRATOR: And
a Philadelphia refinery

pays the price
for failed inspections.

(EXPLOSION)

(DRAMATIC MUSIC PLAYING)

(CAPTIVATING
INSTRUMENTAL MUSIC PLAYING)

NARRATOR: In Minneapolis,

engineers are trying to learn
why the I-35 bridge collapsed.

Some answers are clear.

A key component is weak.

The gusset plates
are half as thick
as they need to be.

NARRATOR: A new
road surface adds weight.

You've got a new bridge deck
that's added an enormous amount
of mass to the structure.

NARRATOR: But is there
a moment when the bridge
could have been saved?

(SUSPENSEFUL MUSIC PLAYING)

In June 2003,

engineers are carrying out
a routine inspection
on the bridge

when they notice
something disturbing.

At a pair of joints called
U10 east and U10 west,

they see the steel plates

holding the bridge together

are bending.

Why wasn't this clue
seen before?

BISBY: In the structural
engineer's psyche,

the joint is always
stronger than the beam.

So you don't have to
check gusset plates

because they're
always much stronger
than the elements, right?

So, you don't look at them.

(CAMERA SHUTTER CLICKING)

NARRATOR: They photographed
the bent plates.

But these warning signs
are somehow ignored,

because the engineers
believe they're unbreakable.

Gusset plates don't fail,
so seeing a gusset plate bowed,

it may have been determined
that maybe it was during
erection or something

that it got bent a little bit.

DICKRELL: The engineers say
it's probably not a big deal

because it's been
there for so long.

"We'll deal with it
further down the road."

NARRATOR: A critical chance
to repair the faults
is missed...

Four years before the bridge
ultimately fails.

(DRAMATIC MUSIC PLAYING)

But miss a warning sign,
however small,

and it can have
dire consequences,

as a huge disaster
in Philadelphia proves.

The biggest oil refinery
on the east coast,

spread across a massive
1,400-acre site.

If you think about
a theme park
like Six Flags,

it's like then times
the size of Six Flags.

The really crazy thing
to think about

is the amount of energy
they process.

It's bigger than the biggest

nuclear weapon
in the U.S. arsenal.

It's bigger than that.

NARRATOR: The potential
for disaster is terrifying.

So engineers regularly
inspect its 950 miles
of pipes for faults.

But just like at the I-35,

they miss a vital weakness
at a critical joint.

It is a chemical engineer's
worst nightmare.

NARRATOR: A leak of
highly flammable propane gas.

HENRY: My God. We use it
to do barbecuing, right?

Lots of energy
in a small volume.

(SUSPENSEFUL MUSIC PLAYING)

NARRATOR: Forty seconds
after the gas appears...

(EXPLOSION)

The blast is so powerful
that a 19-ton steel tank

is blown 2,000 feet away
across the other side
of the river.

And the shock is felt
as far away as New Jersey.

MAN: Holy (BLEEP)!

Look at that,
it's a (BLEEP) bomb!

NARRATOR: Miraculously,
no one dies.

The failure is initiated
at one single piece of pipe,

an elbow joint.

And critically, this is a piece
of the processing plant

that has not been
inspected over the years.

NARRATOR: This faulty pipe

has been slowly corroding
for over 40 years,

until it's worn down
to half the thickness
of a credit card.

Then it reaches
breaking point.

In these types of
heavily engineered environments,

one small factor,
if it goes wrong
and goes unchecked,

can cause catastrophe.

NARRATOR: Coming up...

With the warning signs ignored,

a perfect storm
is brewing for the I-35.

All this bridge needs
is one extra nudge.

(DRAMATIC MUSIC PLAYING)

NARRATOR: In Minneapolis,
the I-35 bridge is in trouble.

Through its 40-year life,
a series of engineering errors

has pushed it
to the brink of collapse.

But in its final hours,
what tips it over the edge?

(SUSPENSEFUL MUSIC PLAYING)

With just three hours
to disaster,

a construction crew,
loaded with materials
and equipment,

heads onto the bridge
to make routine repairs.

They start to stockpile
construction equipment

and gravel on the surface
of the road deck.

Unfortunately,
they've placed this load

right on top of
the joint at U10.

NARRATOR: The exact place
where the plates are bending
to breaking point.

It's a very
unfortunate occurrence

because you have
all of this additional load

now concentrated directly
on top of the weakest spot
on the bridge.

NARRATOR: Over
300 tons of equipment,

including cement trucks
and heavy machinery

is now stacked up,

and the final blow
is on its way.

(CLOCK TICKING)

A little after 6:00 p.m.,
right at the height
of rush hour,

cars are streaming
across the bridge.

NARRATOR: With
the construction crew
blocking two lanes,

traffic builds up
and comes to a standstill.

There are over
100 buses, cars, trucks,

slowly filling up
each inch of the bridge.

NARRATOR: One hundred vehicles

adds another
half million pounds
to the strained structure.

(HORN HONKS)

(CLOCK TICKING)

Midway across the bridge,
Lindsay Walz.

The traffic started
to slow down.

I'm hot, I'm tired
at the end of a long day,

and I just wanted to get home.

The load on the bridge
is almost as big as
it's going to get.

(CLOCK TICKING)

NARRATOR: Approaching
from the opposite direction,
Andy Gannon.

I knew they were working
on both the outside lane

and the inside lane
of the bridge.

So I knew it was
going to be crowded.

This is the most weight
that this bridge has ever had
in its 40 years.

(CLOCK TICKING)

NARRATOR: Now the 111th car
rolls onto the bridge,

and it's the final straw.

(MACHINERY RATTLING
AND WHIRRING)

(CLOCK TICKING)

(DRAMATIC MUSIC PLAYING)

I see waves of concrete
lifting up cars

and dumping some of them
over into the river.

I'm waiting for it to come
to me

and we all go down as one.

My car doesn't actually
really stop moving

until it lands at the bottom
of the Mississippi.

I was drowning.

I had to get out of my car
or that would be where I died.

I knew that my time
was absolutely running out.

And I kicked and I swam
and I surfaced.

A construction worker
brought a broom handle
to fish me out.

I assumed that I was
one of a handful
of survivors at best.

NARRATOR: Meanwhile,
Andy Gannon's car
has fallen 50 feet

onto an unstable
island of concrete.

He scrambles from his
silver Chrysler to escape.

GANNON: I thought to myself,
we're going to continue

to drop in the water
at any minute.

NARRATOR: But he stops
in his tracks

when he sees a bus
full of terrified school kids.

I'm hearing people,
and the screams from
the school bus is what I hear.

-(SIRENS WAILING)
-(CHILDREN SCREAMING)

Holy smokes,
I've got to go help.

(MAN SPEAKING ON RADIO)

A couple seconds later,
there's probably
four or five adults,

we took the kids
off the school bus

and handed them down
to individuals that were
on the River Road.

(INDISTINCT CHATTER)

(HORNS HONKING)

Then I see black smoke
coming out of the cab
of the truck.

(MAN SPEAKING ON RADIO)

I could hear him...
Hear him screaming.

NARRATOR: As smoke
turns to fire,

there's nothing Andy can do.

He didn't make it and...

And, you know, that's, uh...
That's probably the...

The worst part
about the whole thing.

(AMBULANCE SIREN WAILING)

NARRATOR: The collapse
takes a grim toll.

Thirteen dead, 145 injured.

Minneapolis is a city in shock,
and a city looking for answers.

(SOMBER MUSIC PLAYING)

(GENTLE
INSTRUMENTAL MUSIC PLAYING)

(GENTLE
INSTRUMENTAL MUSIC PLAYING)

(PEOPLE SCREAMING)

(DRAMATIC MUSIC PLAYING)

NARRATOR: Big disasters
can have obvious causes.

But sometimes,
engineers have to
search for the answers.

(911 OPERATOR SPEAKING)

(WOMAN SPEAKING)

I'm in a fog, I'm in shock.

I started to look up above me,
where the bridge had been,

and I couldn't understand
what had happened
to me just then.

NARRATOR: The sudden collapse
of the I-35 bridge
leaves everyone guessing.

But what really happened?

Seen through
the eyes of engineers,
the clues are clear.

A flawed design...

If you fracture one piece
of the bridge,

the whole structure comes down
like a house of cards.

NARRATOR: ...a deadly error...

Unfortunately, some of these
gusset plates

are only half as thick
as they should be.

NARRATOR: ...extra weight
added to the bridge...

A large concentrated force
above the weakest point
of the bridge.

NARRATOR: ...and
warning signs ignored,

until finally,
failure is inevitable.

(CLOCK TICKING)

(DRAMATIC MUSIC PLAYING)

At the gusset plate that fails,

the stresses become so high

they start overcoming
the capacity of
the gusset plate itself.

And the truss beam that's
connected to that gusset plate
pushes through the joint

and completely destroys
the node at U10 west.

NARRATOR: The plates
at U10 are ripped apart.

DICKRELL: With those
gusset plates gone,

there is no way
for the truss bridge
to hold itself together.

PROCTOR: The whole
center section
of the bridge snaps

and begins to drop down.

BISBY: And in the CCTV footage,

we can see that
the north end of the bridge
collapses slightly later.

There's this
sort of domino effect

as the structure fails
from south towards the north.

BELL: In the space
of about seven seconds,

the whole bridge,
that's stood there for 40 years,

is completely gone.

(SIRENS WAILING)

NARRATOR: It's
an engineering catastrophe

no one in the Twin Cities
will ever forget.

That was our 9/11.

No disrespect,
I'm not comparing them,

but that was our bad day,
our failure, our, um, loss.

Sometimes, I look back
and think, you know,
this shouldn't have happened.

I've thought a lot about that.

I've thought a lot about
who put that concrete there,

who measured
those gusset plates,

who was that inspector
who took a picture of
that bent gusset plate?

GANNON: What's the next thing
that's going to break?

Can I trust anything anymore?

How do we make sure
it doesn't happen again?

Just 10 weeks after
the I-35 was destroyed,

construction of a new bridge
begins across the Mississippi.

NARRATOR: In September 2008,

the new I-35 West,
Saint Anthony Falls Bridge,
opens.

It's a symbol of
doing what we can
to put the past behind,

yet never forgetting the people
that were impacted by this,

and still are impacted
by this to this day.

NARRATOR: This bridge
learns from past mistakes.

A state-of-the-art smart bridge
with sensors everywhere.

So as cars cross,
their safety is guaranteed.

The bridge can actually tell
the people who are operating it
how it's feeling,

what kinds of strains
and stresses and forces
is it being exposed to.

NARRATOR: It's built
with reinforced concrete.

And if one part
of the bridge fails,
the rest will stay standing.

It's a bridge
for the 21st century.

LAURITSEN: The old bridge
before the tragedy,

nobody ever thought about it.

The new bridge,
people think about it
all the time.

And when you drive over
the new 35W bridge,

you're like,
"Wow, I can't believe
what happened here."

You don't feel like
it's going to go back to that.

You feel like
we learned from our mistakes.

NARRATOR: But not all
of our bridges are new.

And despite engineers'
best intentions,

nothing is ever 100% safe.

Between 1980 and 2012,

over 1,000 bridges
failed across the country.

And when these big,
strong structures go wrong,

they can quickly turn
into catastrophe.

Unlike a surgeon,
who may cause the death

of a single person
if they get the surgery wrong,

an engineer can
very easily cause the deaths

of hundreds
or thousands of people,

and that's something
that all structural engineers

need to keep very clear
in their minds.

(PEOPLE SCREAMING)

BELL: Bridges will collapse,

ships will sink
and airplanes will crash

if mistakes are made.

(DRAMATIC MUSIC PLAYING)

But everyone should rest assured

that right at the top
of an engineer's list

is to learn from those
mistakes.

NARRATOR: This season on
When Big Things Go Wrong...

MAN: Oh, my God.

...a horrific building
collapse in New Orleans...

When big things are pushed
beyond their limits,

the results are catastrophic.

NARRATOR: A devastating
plane crash in San Francisco...

BELL: It's amazing to think
that something as small
as a grain of sand,

can bring down something
as big as a major airliner.

NARRATOR: A mysterious
cruise liner collision
in Italy.

There's a problem
with the engine.

The throttle is turned
on full thrust.

NARRATOR: Engineers
unlock more clues

behind the world's
biggest disasters.

When something goes wrong,
it goes really, really wrong.