All language subtitles for Fatal.Engineering.S01E02.1080p.WEB.h264-FREQUENCY_track3_[eng]

[narrator]
Every day, around the world,
millions of motorists take

to the roads and bridges.

These marvels of design have
pushed the boundaries

of physics and engineering
since their creation.

[Ian] We're engineers.

We design things to survive.
We don't design things to fail.

[Rob] But when things go wrong,
their collapses are

spectacular and unforgiving.

In 2018, 43 people lost
their lives when torrential

rain caused the Morandi Bridge
in Genoa, Italy, to collapse.

Their journey to
the peace and tranquility

of the Italian coast
will become a nightmare.

In 1940, in the state
of Washington,

in the USA, the Tacoma Narrows
Bridge, just months after

its inauguration, broke apart
due to an oscillating motion

never before observed
on a bridge.

You don't have to be an expert
to see that it's only going

to end in one way.

In 2007, a single structural
element of the I-35W highway

bridge in Minneapolis failed,
causing the entire structure

to collapse, killing 13 people.

[Ian] It's just like
a house of cards.

You pull one card out,
the whole thing falls down.

What lessons did we learn from
these catastrophic tragedies?

How did the engineering
community and the institutions

responsible for maintaining
these impressive

structures respond?

And what has been done
to ensure that bridges designed

today avoid fatal engineering?

[electronic theme music playing]

[suspenseful music playing]

When it was inaugurated
in Genoa, Italy, in 1967,

the Polcevera Viaduct,
more commonly known as

the Morandi Bridge was widely
celebrated as a masterpiece

of engineering.

To the north, it is supported
by a series of fairly

standard piers.

In the south, the pillars
are very different.

It has these three Pylon
structures, which are very,

very visually dominant
in the city.

Each tower has four connection
points, with two stays

stretching in either direction
of each Pylon.

This unique triangular design
is the trademark

of its designer,
the Italian engineer

Riccardo Morandi.

He had already experimented
with it on the Maracaibo Bridge

in Venezuela a few years
earlier, a bridge eight times

larger than the one in Genoa,
which has already

proved its worth.

He's a brilliant man.

He's already well known
for doing, you know,

pretty unusual designs.

It's not just
an ordinary bridge.

But on the 14th of August,
2018, it's one of these,

the vital component
to the collapse of the bridge.

[cracking, rumbling]

[suspenseful music playing]

It's 11:35 a.m.

In the middle of August,
many motorists traverse

the Morandi Bridge, part of one
of the busiest routes in Italy.

[Shini]
Whether on holiday or simply
going about their daily lives,

disaster is imminent.

The Morandi Bridge
is destined to fall.

-[thunder rumbling]
-[suspenseful music playing]

No one, not even the engineers
and inspectors responsible

for ensuring the safety of
the bridge, foresaw the tragedy

that was about to unfold.

People inside their cars,
as they're driving along,

minding their own business,

suddenly, seemingly out of
nowhere, dropping 40-odd meters

into the valley.

11:36 a.m.

A stay cable on Pylon 9 breaks,
causing 250 meters of deck

to collapse just under
a quarter

of the total length
of the bridge.

[cracking, rumbling]

Tons of concrete,
and the vehicles on the bridge

plunge into the Polcevera River,
also falling

into the railway tracks
and buildings below.

[shouting in Italian]

[sirens wailing]

[helicopter whirring]

The collapse killed 43 people
and injured many others.

For the people of Genoa
and those close to them,

it has become clear that
this visionary bridge,

emblematic of the city,

has become a symbol of
a fatal engineering flaw.

[speaking Italian]

[in Italian]

[Ian] This is another one
of those cases

where the engineering community
around the world looks

in horror --
and in this case,

sadly, many people died --

and asks themselves,

"Why? Why has it happened?"

To understand why
the Morandi Bridge collapsed,

it is essential to consider
the materials used

in its construction.

[airplane humming]

[explosions blasting]

After the second world war,
with the production

and availability of steel
considerably reduced,

architects and engineers turned
to other materials

for their projects.

For Riccardo Morandi,
it was concrete.

[Rob]
Riccardo Morandi was fascinated
by the material properties

of concrete.

Prestressed concrete is
subjected to compressive forces

by means of cables tensioned
before any loads are applied.

This unique
construction technique,

invented in the 1920s by French

engineer, Eugène Freyssinet,

requires real craftsmanship
to work perfectly.

[Ian] But the thing that is
particularly important

in the story we're going
to be talking about is

the cable stays.

With a length of 86 meters,
between the top

of each Pylon and the deck,
these prestressed concrete

stays, hailed for their
elegance and unfailing

strength, are responsible for
keeping the deck in the air.

However, it does not have
the same properties as steel.

Concrete as a material
is very good under compression.

It can resist being squished
very, very well.

[Ian] But if you put tension in
concrete, it's gonna crack,

and that's no good.

To prevent the concrete from
cracking, smaller cables are

placed in a sheath
around the other cables

inside the concrete.

But as motorists drive over
the Morandi Bridge,

they have no idea that one
of these stays is

severely compromised.

[Shini]
The pre-stressed concrete would
be tested beyond its limits.

-[cracking, rumbling]
-[shouting in Italian]

In its first year of existence,
the Morandi Bridge was used

by around 5 million vehicles.

50 years later, a year before
its dramatic collapse,

traffic had increased five-fold
to 25 million vehicles a year.

Not only the volume,
the weight of traffic

on the bridge has also
increased dramatically.

Cars are bigger,
more people are moving,

but also the increase
in the amount of freight

from the nearby port.

The port of Genoa is
the largest port in Italy

and one of the most important
in Continental Europe.

Heavy goods vehicles have
to cross the Morandi Bridge

in order to leave the port.

Every time a vehicle crosses
the Morandi Bridge,

the structure
and its concrete stays

are subjected to
varying loads.

These changes in weight
have the effect

of deforming the structure.

As the Morandi bridge
continued to strain

against the ever-increasing
demand of traffic,

cracks began to form.

The cracks allow a silent
and relentless threat

capable of destroying even
the strongest structures made

of concrete and steel.

Genoa is a coastal city
where salty sea air,

precipitation, and heat are all
part of the climate.

Any metal exposed to these
conditions would rust

and if left untreated,
could fail.

The problem with these cables
inside that concrete sheath --

you can't inspect them, apart
from just the outside surface,

and you just don't know
what's going on inside.

The first to express concern
was Riccardo Morandi himself,

12 years after the inauguration
of the bridge,

he is publicly declaring that
he is concerned about the level

of deterioration
he is observing

on his prestressed
concrete stays.

The Italian engineer proposed
solutions to prevent any

further corrosion
on or inside the structure.

The problem is nobody
did anything.

It was not until the 1990s
that repairs were carried out

on Pylon number 11.

Aware of the deterioration
of the materials over time,

authorities commissioned
a detailed report and analysis

of the condition of the stays.

[Rob] It was discovered that
30% of the cables inside

the concrete casing on Pylon 11
had corroded,

resulting in a 50% loss
of load capacity.

But it's not the only one.

Pylons 9 and 10 are
in an equally damaged

and worrying condition.

Restoration work is
being carried out

to reinforce the Pylons.

[Rob] Steel reinforcements were
added to the cables on Pylon 11

to bring back
that load capacity.

But in doing so, it ruins
the clean aesthetic

that Morandi was after.

A few years later,
more modifications were made

to the cable stays on Pylon 10,
this time steel

cradles installed at the top
of those cables.

But nothing was ever done
to Pylon 9.

[Ian] The plan is...

we're gonna do those
in a few years' time.

Unfortunately,
we never got there.

[Shini] Pylon 9 was left
as originally designed.

This was a fatal error.

A fatal error, the gravity
of which the whole world

will realize
on August 14th, 2018.

The time is 11:35 a.m.

It's lashing with rain,
and there's water on the roads,

adding even more weight.

[suspenseful music playing]

The torrential rain
on the Morandi Bridge pummels

the prestressed
concrete stays.

The water is spreading inside,
relentlessly damaging the steel

cables, which have
no waterproof protection.

The cables have corroded to
such an extent, they just could

not cope any longer.

This is when the next event
comes into play.

One vehicle is on the approach
to Pylon 9, a 44-ton truck.

11:36 a.m.

The heavy truck arrives
at the Pylon and triggers

the start of a chain reaction
that will be fatal

for the Morandi bridge.

When the wheels of such
a truck hit a step,

it creates a big impact.

So that truck is most likely
to be the cause of what

started the collapse.

But ultimately,
it didn't need very much.

At that moment,
one of the cables snaps.

They break one after the other,

leading to the total failure

of the shroud.

But it's creating
a new phenomenon.

If one of the cables snaps
on one side of the tower,

the tower itself becomes
unstable and imbalanced.

It's pulled the other way.

So almost immediately after
the snapping of the cable,

the tower collapses
and the bridge deck breaks.

A section just under 250 meters
in length, centered on Pylon 9,

gives out.

Any car on that section at that
time was going down with it.

[sirens wailing]

The vehicles plummeted
45 meters, the height

of a 13-story building.

[somber music playing]

Some died from the impact
of the collapse.

Others survived the drop,
but were then crushed

by falling pieces of concrete
from the tower.

A total of 43 people
were killed

when the Morandi Bridge
collapsed.

This led to a one-year state of
emergency in the Genoa region.

It highlighted
the catastrophic state

of Italy's infrastructure.

The company in charge
of the bridge,

Autostrade, underwent
a partial nationalization,

offering to settle the legal
case against the company

for 1 million euros in damages

and a further 26 million euros
in compensation.

[cracking, booming]

Although Pylons 10 and 11
remained intact

after the collapse
of the Morandi Bridge,

they were demolished
on June 28th, 2019.

A replacement bridge,
the Genoa St. George Bridge,

was inaugurated 13 months later
on August 4th, 2020.

A single moment brought
about by years of negligence

and a refusal to fully
address evident issues can be

catastrophically fatal.

Wednesday, August 1st, 2007,
in Minneapolis, Minnesota.

It's 6:00 p.m.

rush hour on Interstate 35
West, commonly known as I-35W.

As part of that road,
there's a bridge.

[suspenseful music playing]

A very, very busy bridge
crossing the river,

carrying thousands of vehicles
every day.

The I-35W Highway Bridge
has three main spans

made of steel and concrete.

And a truss is a bridge where
the elements are usually

diagonals, and all
the pieces are working

in tension or compression.

And this truss carries
all the load, enables the thing

to support all the traffic.

It's a very efficient kind
of structure.

[Rob] But this bridge will
become one of the most famous,

or should I say infamous,
in American history.

It's 6:00 p.m.
Rush hour on Interstate 35 West

commonly known as I-35W.

What they don't know
is that this routine drive

will turn into
a major catastrophe.

6:05 p.m., 40 years
after its inauguration,

the I-35W highway bridge
collapses.

Happens in the blink of an eye.

[Shini] The bridge gives way,
throwing all

vehicles, passengers,
construction workers,

and equipment down
into the cold waters

of the Mississippi River.

The accident kills 13 people
and injures 145.

Though authorities initially
investigated a terror attack,

this was a disaster that had
been 40 years in the making.

At first glance, the I-35W
Highway Bridge is a solid

structure, perfectly adapted
to its environment.

It's made up of interconnected
steel beams, ensuring that

loads are distributed evenly.

But all of those members have
to be joined together to create

the overall truss.

And usually, when we're doing
this in a system where

everything is bolted or riveted
together, we use a thing called

a gusset plate.

The gusset plate,
this small steel sheet

will be one of
the key elements

that will make the Minneapolis
Bridge one of the most tragic

bridge collapses.

More than 200 of these are
riveted on both sides

of the lattice junction points.

Although small,
they create essential links
in the bridge.

Each one must transfer
the weight

from one element
to another.

[Ian] The load transfers out
of the member into the rivet,

from the rivet, into the gusset
plate, from the gusset plate

into the rivet of the other
member, and then from the rivet

of the other member
into the other member.

It's the gusset plate that will
take the stress of all of those

forces together.

So getting the right thickness
of gusset plate is absolutely

crucial to the strength
of not only that joint,

but to the strength
of the structure as a whole.

Investigators discover
that the builders of the bridge

neglected the thickness
of these plates.

At just 13 millimeters thick,
the gusset plates on the I-35W

bridge were not strong enough
to support the bridge's weight

and that of the traffic.

It was designed to cope with
the heavy traffic

of a region like
Minneapolis with a population

of 3 million,
but in 2007,

100,000 vehicles
cross it every day.

As commuters head home
on August 1st, the safety

of the I-35W does not enter
their mind.

Having been a key route through
the heart of Minneapolis since

it was reopened in 1967,
there's no reason for fear.

But some warning signs were
already apparent,

because on that day, traffic
on the bridge is disrupted.

On the day in question,
there are new modifications

being made to the bridge.

[Shini]
Heavy machinery
and building materials

ready to resurface
the bridge's deck.

Four of the eight lanes
of the 35-meter-wide deck were

once again closed
for renovations, renovations

that don't worry drivers.

[Rob] They've seen it
for months, though.

It's nothing
out of the ordinary.

What is out of the ordinary is
what's happening beneath

the bridge deck.

The renovations are underway to
combat an almost hidden threat,

a dangerous process that is
slowly but surely eating away

at the structure,
another bridge falling victim

to corrosion.

This relentless enemy is fed
not only by the river

that the bridge crosses,
but also by the only natural

waterfall on the Mississippi,
875 meters downstream.

Saint Anthony Falls.

The spray from the falls
directly attacks the concrete

slab on which the cars drive.

But it's not the only factor
damaging the bridge.

If you've ever spent a winter
in Minnesota, you know

that the winters get brutal.
The temperatures plummet.

There's ice.
There's lots of rain.

And so the authorities,
as we do all over the world,

use salt on the roads to melt
the ice and make it safer

for drivers.

While cold and water are real
threats, salt adds

its corrosive power
to the concrete slab,

and, more importantly,
to the steel bars

that reinforce it.

To avoid this,
they add concrete to the deck.

Several tons will be added
to the initial weight.

The bridge is designed to
support this increased weight,

but this isn't the first time
weight has been added.

Because when it started life,
it was only six and a half

inches thick, 165 millimeters,
and that's super thin.

[Shini]
Moisture and salt used during
the winter months to de-ice

the road would slowly seep
into the concrete and corrode

the metal within.

In the years following
its inauguration,

the concrete deck
began to crack.

To address this issue,
engineers took a major decision

in 1977, only 10 years after
the bridge's construction.

They poured more concrete
on top to protect and renew

that surface so that the bridge
deck was structurally sound

despite all the environmental
factors that were trying

to constantly attack it.

However, this added 512 tons
to the bridge's initial weight.

They don't know it yet,
but this is the beginning

of a nightmare scenario
that will slowly but surely

doom the I-35W highway bridge.

Drivers crossing the bridge
couldn't know

that the structure was now much
heavier than when it was built.

But the experts should have
realized this during

a previous inspection.

It's really important that
engineers are sent out to do

detailed inspections
and analyses of structures like

the I-35 West Bridge.
And that happened.

In fact, it happened four years
prior to this disaster.

And there is evidence
from those engineers' reports

of the smoking gun
in this disaster.

This is the photograph that
showed signs of the already

impending catastrophe.

This image shows gusset plates
and shows signs of warping.

As an engineer, when you see
a component that's started

to bow, like this gusset plate,
that tells you that the forces

within your structure are doing
something different to how

they were originally designed.

The consequences would be
dramatic because, although very

solid, the I-35W highway bridge
has an Achilles heel.

This is known as
a non-redundant bridge.

[Rob] It means that there are
no redundancies built

within the structure.

If one member
in the truss fails,

then the whole bridge can fail.

To avoid that kind of disaster
scenario, all parts of a bridge

like this must be perfectly
calibrated and inspected.

However, the bending of this
gusset plate was not considered

a danger by inspectors.

The rivets
and the buckling plate

experience fluctuating stresses
all the time, and that causes

something called fatigue,
which eventually creates

a crack, and then if
the loading continues like that,

that crack will grow
and as the crack grows

eventually there'll be
a point when...bang.

During the fateful day
of August 1st, 2007,

construction workers prepared
the materials needed to add

the additional layer
that evening.

571 tons of sand and gravel
ready for concreting,

and a 36-ton tanker are now
on the bridge.

In total, more than 600 tons
of material were added

to the structure above
the bent gusset plate.

After years of development,
which increased

the dead load of the I-35W,
this added weight is placed

directly above a weakened
pressure point.

At 6:00 pm, everything was in
place for the bridge workers

to continue with the deck
renovation work.

They have to start
their shift at 7:00 pm.

What they don't know is that
by 7:00 pm,

there'll be no bridge left
to resurface.

6:03 pm...

It's rush hour.

People are making their way
home from work.

They're crossing the I-35
bridge in huge numbers.

But that gusset plate has now
got to the point where

it can't take it any longer.

The micro cracks within
that gusset plate have grown.

The gusset plate fails,
and it fails catastrophically.

6:05 p.m., the beginning
of the end

for the I-35W Highway Bridge
and tragedy for those on it.

The members that are connected
to it detach.

They're no longer attached
to each other,

the force has got nowhere to go,

so it just collapses
and it collapses instantly.

[cracking, rumbling]

The central span collapses,
sending vehicles,

people, and building materials
plummeting 35 meters,

17 vehicles fall
into the Mississippi River.

Some are crushed by the deck's
pieces falling on them,

but there's more to come.

After the central span
collapses,

the two adjoining
spans follow.

Everything falls
into a railway yard,

and the Mississippi River.

111 vehicles, including
25 construction machines

and a school bus loaded with
63 students, were on the bridge

when it fell.

While many miraculously
come out of the disaster alive,

for others,
a new nightmare begins.

Emergency services take
six minutes to reach

the accident scene.

In the meantime, solidarity is
building among the survivors

who are trying to rescue people
trapped in their cars,

which are filling up
with water.

The collapse of the I-35W
Highway Bridge injures

145 and leaves 13 people dead.

The I-35W bridge became fatal
for three main reasons.

Firstly, the design
of the gusset plate has to be

up there as being
a major problem.

Number two is the question
of maintenance.

Maintenance is vital.

And number three, actually,
is that the bridge is carrying

more load than it was
designed for.

As it turns out, that problem
was not located purely

within Minnesota.

In 2007, the Federal Highway
Administration counted 19,273

non-redundant bridges
in the United States alone,

465 of which had a steel truss
similar to that of the I-35W.

Of those, 31%,
or 145 bridges, were classified

as structurally deficient.

On all these bridges,
if a key structural element

were to fail, the bridge
would present a high risk

of partial or total collapse.

In memory of this tragic
accident, the defective gusset

plate is now exhibited
in a museum in Minneapolis.

It's a haunting reminder
that many people that failures

like this could become
all too common.

[Rob] What is unique is what
happened on the other side

of the country, in
Washington state, when, in 1940,

a bridge ripped itself apart.

The famous, iconic
Tacoma Narrows bridge.

[Ian] Tacoma Narrows Bridge
represents one of those moments

in history where
everything changed.

There's a before Tacoma
and there's an after Tacoma.

11:09 a.m.
on November 4th, 1940.

A little more than four months
after its inauguration,

the cameras of the reporters on
site capture these exceptional

and unprecedented images
that leave people speechless.

It's overcast and the wind
is already causing the bridge

to showcase its
wave-like motion.

11:10 a.m.

The brand-new Tacoma Narrows
Bridge collapses spectacularly

in this inlet
of the Pacific Ocean.

The deck, now twisting
in unpredictable motions,

continued to shed concrete
and steel, with successive

portions of the bridge
falling into the water

of the narrows below.

Hailed as a triumph of human
perseverance when it was

inaugurated, the Tacoma Narrows
Bridge would become a symbol

of contemporary
engineering failure.

Why was such an important
bridge destined for disaster?

In 1937, the local authorities
decided to build a bridge

to link the cities of Tacoma
and Gig Harbor.

[Shini]
It's intended to help commuters
traverse the cold waters

of the Puget Sound,
providing a vital economic

and military route.

[Ian] The way to get
from one side to the other was

a very long way around.

So this is a really good
example of where a bridge is

gonna make a massive
difference to people's lives.

An initial design was proposed
by a local engineer,

Clark Eldridge.

Clark Eldridge is proposing
a steel truss bridge, of which

there are thousands at this
time in the United States.

Its design incorporates
7.6 meter-deep trusses

to reinforce the rigidity
of the bridge.

But at a cost of 11 million US
dollars, or at today's value,

$250 million,
the Eldridge Project is

considered too expensive.

[suspenseful music playing]

[Rob] On the other hand,
you have Leon Moisseiff,

who is a steel rope expert,
and he is proposing a sleek

suspension bridge.

But crucially, the suspension
bridge will do

that job cheaper.

At $8 million US dollars,
$3 million less

than the Eldridge project,

the proposal by this
experienced engineer,

who has worked
on the Manhattan Bridge

in New York and the Golden Gate
Bridge in San Francisco,

also has other advantages.

[Ian] It was using
less material.

It was gonna be easier
to build.

So that design was selected.

The Léon Moisseiff Bridge
is supported by

two 130-meter-high towers,

linked by cables that suspend
the deck 60 meters

above the waters
of the Tacoma Narrows.

The longest span is 853 meters,
making it the longest

suspension bridge in the United
States and the third longest

in the world.

The engineer did away
with the usual steel trusses

and replaced them with two
2.4-meter-high girders

along the deck.

It's very, very thin,
like a ribbon,

but also because it's
very narrow.

With a deck only 12 meters
wide, the length of three cars,

the bridge's visionary elegance
was to become the weak point

of this revolutionary
work of art.

July 1st, 1940.

The cameras and the public
flocked to the inauguration

of what is regarded as
a masterpiece of engineering.

[Shini] What locals don't know
is that the bridge is

already doomed in his efforts
to create a visually pleasing

cheaper bridge, Moisseiff made
fatal miscalculations.

[Rob] Very early on the workers
are regularly subjected

to high winds that are funneled
down this valley.

The wind...

one of the main enemies of
a bridge, that absolutely must

be taken into account
when designing it.

If it was a truss bridge,
then obviously the wind would

pass through it to an extent.

Unlike trusses, these girders
don't allow wind

to pass through.

Although visionary,
Leon Moisseiff's proposal

to replace the trusses
with steel girders on the sides

of the deck...

would be the first mistake
that would prove fatal

to the Tacoma Narrows Bridge.

[Ian] The wind hits the side
of the bridge,

and it's presented
with an eight-foot-deep girder,

which is a solid object.

And the wind, of course,
has to go somewhere.

As the wind hits the truss,
it creates small vortices.

These vortices move along
the truss and find a completely

new direction when
they reach the edges.

[Ian] Well, it goes over
the top and underneath.

The wind separates from
the structure, and that creates

a little vacuum, a little area
of low pressure every time one

of those vortices forms.

That pressure creates a sort
of suction which draws

the bridge down
if it's on the bottom,

and if it's on the top,
it'll draw the bridge up.

[Rob] You may think of bridges
as rigid, stationary structures.

In fact, all bridges are
designed to have some movement,

some flex in them.

Despite these worrying signs,
the bridge was open to traffic.

The bridge's strange behavior
earned it the nickname,

"Galloping Gertie."

From day one, the bridge deck
sways, it moves, it dances

in the wind.

Some people enjoy the process
of driving across it,

almost like being
on a roller coaster.

Engineers are concerned because
this amount of movement was not

part of the design process.

They are attempting to
stabilize the deck by securing

it at both ends using cable
connected to 50 ton concrete

blocks on the bank.

[suspenseful music playing]

But they break.

Two months after
the inauguration of the bridge,

hopes were pinned on a team
of engineers and scientists led

by Professor Farquaharson from
the University of Washington.

They are building this
miniature replica of the bridge

and carrying out tests
to reproduce its exact behavior

when the wind blows.

They have come up
with two proposals

to stop its undulations.

[Rob] The first proposal is to
drill holes in the steel girders

along the side of the bridge
so that the wind has a passage

through and doesn't have to go
up and under the bridge.

[Shini]
The second is to add deflector
veins and fairings along

the deck to increase
the bridge's

aerodynamic profile.

The first option is rejected
because of the irreversible

nature of the solution,

but the second must
be implemented.

Unfortunately, the Tacoma
Narrows Bridge would not hold

out long enough
for work to begin.

November 7th, 1940.
The time is 10:30 a.m.

Winds of 68 kilometers per hour

blow across
the Tacoma Narrows Bridge.

It's waving up and down,
oscillating up and down

and side to side, as it has done
for months before,

but the bridge starts to move
in a slightly different way.

A phenomenon never before
seen on a superstructure.

The very thin deck, praised for
its elegant design, is proving

to be the second weak link
of the Tacoma Narrows Bridge.

[Ian]
This bridge, which had
longitudinal girders

down each side, had very
little transverse stiffness.

The bridge deck has started
to twist, and that twisting

movement was the fatal
difference on this day.

Faced with the terrifying sight
of this deck twisting along

its entire length,
the engineers are

increasingly worried.

The bridge is immediately
closed to traffic.

The time is 10:31 a.m.

[Shini]
Unfortunately, one driver
has already been allowed past

and is on a deadly route
towards the bridge.

Leonard Coatsworth.

It's just him and one passenger
in his car.

His dog, named Tubby.

[dog barking]

Tubby and his master
find themselves

stranded in the middle
of the raging bridge.

[Shini]
As the bridge sways almost
uncontrollably, a major failure

goes unnoticed.

A cable band at the bridge's
mid-span snaps.

[dog barking]

Leonard can't go any further
and he can't go back.

He decides to abandon his car.

[Shini] He climbs out, desperate
to make it to safety with Tubby,

but is knocked from his feet
by the powerful twisting motion

of the concrete, throwing him
first to one side of the bridge

and then back to the other.

Tubby, still sitting
in Leonard's car and terrified

by the movement, refuses
to leave the vehicle.

Leonard has to accept
the inevitable if he wants

to save himself.

11 a.m.

Professor Farquharson came
to observe the new torsion

behavior of the bridge.

He's about to witness something
completely new, and even

more dangerous.

As the bridge continues
to sway, it draws its power

from the winds that continue
to batter the deck.

Not only is Galloping Gertie
twisting out of control,

it's also building energy.

There is a critical point where
the speed of the eddies being

shed coincides with the natural
frequency of the bridge.

It is no longer just the wind
that creates this twisting

movement along the bridge,
but the transfer of energy

within the structure itself,
known as resonance.

It's a runaway train bound
for the end of the track.

To make matters worse,
the two ends of the bridge are

twisting in opposite
directions.

The bridge twists violently up
to 45 degrees in one direction,

and then the other.

This creates a propeller
effect, with only the middle

of the bridge locked in place
while the two sides

twist violently.

11:02 a.m.

A girder bulges out on the gig
harbor side of the bridge,

unable to endure this violent
twisting motion.

The weight that is now put
on the hangers next to it

immediately is too much.

They fail and the whole thing
falls like a domino rally.

[cracking, rumbling]

[Shini] Professor Farquharson
and Leonard can do nothing more

than watch the car and
poor Tubby fall with the rest

of the bridge's main span deck.

Tacoma is one of those moments
in history when everybody just

stops and says, "Wow,
now we've learned something

we didn't know."

It was a phenomenon that
had just not been seen before.

Following the collapse
of the Tacoma Narrows Bridge,

many other suspension bridges
have been built and have become

benchmarks
of structural engineering.

Bridges are icons
within our cities and cityscapes

around the world.

But when things go wrong,
their collapses are

spectacular and unforgiving.

We're engineers.
We don't design things to fail.

We design things to survive.
Sometimes, mistakes happen.

Sometimes humanity has made
the same mistake twice.

Whether it's a design error,
an unknown phenomenon,

or negligence, when a bridge
collapses, the whole world is

in shock.

When these errors are not
caught, then a collapse can

become a tragic case
of fatal engineering.