All language subtitles for Impossible Engineering s08e02 Seattle Super Bridge.eng

In this episode...

This is some of
the most incredible engineering

that I've ever seen.

This is really something
extraordinary.

...The planet's only
floating railroad bridge...

We're essentially putting a rail
on a marine vessel.

It's extremely exciting.

...And the pioneering
historic innovations...

It's impressive.
It's really cool to see this.

...That made
the impossible possible.

Captions by vitac...
www.Vitac.Com

captions paid for by
discovery communications

king county, Washington...

Home to Seattle and Bellevue,

hubs for the nation's
booming tech industry...

...Where the population
is exploding

and traffic is gridlocked.

Engineer John Sleavin lives

and works in a city
pushed to its limits.

There's a lot of
major corporations in Seattle.

The traffic's getting worse.

The need for transportation
is increasing,

and the need
for choices are increasing.

The solution could be
to connect the cities by train,

but king county's
unique environment

can make travel difficult.

One of the unique
features of Seattle

is its geographic terrain.

There are a number of lakes
that all restrict where

and how you can place
transportation services.

In particular,
lake Washington sits between

downtown Seattle and Bellevue,

both of which are high-tech
areas that need to be connected.

In a landscape known
for vast bodies of water,

lake Washington is the largest
and deepest.

Here, traditional bridges
just aren't possible.

But engineers in Seattle
have the answer.

This once impassible lake
has now been conquered

by the incredible
I-90 floating bridges...

...A concrete mega structure
that actually sits

on the surface of the water
unsupported by columns.

This project is
incredibly unusual in that

we're applying systems
that has not been done

by anybody else in the world
ever before.

These extraordinary
buoyant bridges are capable

of carrying 142,000 cars a day.

Nowhere else in the world
has this ever been done.

It's floating. It moves.

With a massive 357,000
tons of reinforced concrete,

the twin floating bridges weigh
more than 52,000 elephants.

All that weight is floating
on 38 monster pontoons

with nothing but 210 feet
of water below the surface,

crossing a span
of over 1.5 miles

and capable of supporting
the weight of rush-hour traffic.

And now engineers are entering

the most challenging
phase of construction,

adding a state-of-the-art
train line

and creating the planet's
only floating railroad bridge.

Once this system is
commissioned and in operation,

this will be an engineering feat
like no other.

But this ambitious project

poses huge
engineering challenges.

Is it possible to connect
a railroad from land

onto a floating moving bridge,

if those rails were
just attached on either side,

that continuous connection
would experience

all those movements at one point

and would probably
snap the rail.

What happens when
a high-voltage current

is introduced to
a structure in water?

There is a risk of stray
current escaping from the rails,

which could get into
the critical bridge structure.

And will the bridge
be strong enough

to support 300-ton trains?

We can eccentrically
load the bridge

and potentially crack it.

That would not be good.

But the biggest
challenge is keeping

this concrete
superstructure afloat.

It is very important

that if there's
any water intrusion,

it won't sink the whole bridge.

The first step
for Seattle�s engineers

was to decide whether they had
to build a floating bridge

or if they could go
with a more traditional design.

Engineer Jim Stonecipher
is very familiar

with the daunting complications
of building on this lake.

The lake is deep

and, being in earthquake
country,

we need a good material
to set our foundations in,

and that's just not available on
the bottom of lake Washington.

Even if engineers were
to sink support columns

through 213 feet of water,

they would then hit a soft
lakebed made of silt and clay.

Pillars would need to go
through another

164 feet of sediment

to reach a solid footing.

Add the column length
needed above the water

and this becomes
an incredibly expensive

and unstable structure.

On the engineering side,

it would be difficult
to build the standard cable stay

or other type of bridge
in that area.

It takes a unique
kind of bridge span

to span lake Washington.

So the engineers' only option

is to float the bridges.

But how can they ensure

the giant concrete structure
doesn't sink?

On the Caribbean island
of Cura�ao,

local engineer Albert Zwueste
is exploring

how a clever piece
of engineering

could help the team
at lake Washington.

The island's main town,
Willemstad, was a perfect port,

but by the mid-1800s,

the deep natural harbor
was creating a problem.

But the channel is 492-feet wide

and 49-feet deep
with a soft sandy seabed,

making most bridges
impossible to build,

especially one that allows
the passage of ships

into the harbor.

But when American ice merchant
Leonard Burlington smith

sailed into Cura�ao in 1876,

he had the answer.

Affectionately known
to the locals

as the swinging old lady,

it's one of the oldest
pontoon bridges in existence.

But the brilliant pontoon design

doesn't just allow for transit
between each side.

The floating bridge
has another trick up its sleeve.

The impressive
548-foot bridge span

is hinged at one corner

and swings open to allow boats
into the harbor.

Smith's design was
brilliant in its simplicity.

And just beneath the pedestrian
walkway lie the vital components

that will prove significant
to the engineers in Seattle.

Pontoon bridges have been
around for millennia,

but few can compare
to the swinging old lady.

Now, on lake Washington,

engineers are taking the idea
of the pontoon bridge

and supersizing it.

King county, Washington,

is one of the nation's
fastest-growing regions.

There's a constant battle to
keep the population connected.

But with the massive
lake Washington in the way,

engineers have been forced

to come up with
an innovative solution...

A pair of gigantic concrete
floating bridges

supported by pontoons.

The pontoons are large enough
to support a highway

carrying 50 million cars a year

and the first
ever floating bridge railroad.

Engineer Jim Stonecipher
is responsible

for maintaining the bridge.

So our solution
to crossing lake Washington

was building
these pontoon bridges.

We make a concrete pontoon
out of very dense concrete

with hollow cavities inside.

The concrete has enough buoyancy
in it

to support the bridge
and the traffic on it.

During construction,

38 giant pontoons
are positioned end to end,

giving the illusion
of one massive bridge base,

each pontoon is divided
into cells and sealed

with watertight hatches.

Two overhanging bridge decks

provide enough space
for eight lanes of traffic

and two train tracks.

One of the reasons
we have so many pontoons

is for redundancy,

so that if one fails,
it won't sink the whole bridge.

Each compartment
has its own door

and sealed off,
kind of like a ship,

and that way, we don't lose
the pontoon bridge

and we can maintain traffic.

Keeping
these mega bridges afloat

is an impressive feat,

and it takes even
more incredible engineering

to keep them from floating away.

Down below us, you're going
to see the anchor cables

that help stabilize the bridge

and keep them in place.

And here comes one now.

You can see it
just below the water.

The longest anchor cable
is about 739 feet

in about 165 feet of water.

Buried in the lake bed,

movements from the bridges

put pressure
on these anchor cables,

causing them to fray.

I got a cable here.

To prevent catastrophe,

a team of divers
working at depths

of up to 165 feet

are currently replacing
damaged components.

The anchor cables
are very heavy,

and it takes a real big team

to get those anchor cables
in place.

So far, 32 huge new
cables have been installed.

But as the seasons change,

so can the tension
of the cables.

From summer to
winter here on lake Washington,

as the lake raises and lowers,

anchor cables become
slack or tight.

And we don't want increased
pressure on the bridge

or we do not want
the cables to be slack.

A rupture in the cables

could spell disaster
for the bridge.

So it's imperative that as
the lake's water level changes,

the anchor cables are adjusted
to the correct tension.

So now we're down
inside of one of 18 pontoons.

Watch your head.
Little rough.

We're walking in through
the anchor cables

in one of the segmented
compartments of the pontoon.

And this is the anchor cable
on the pontoon.

This particular anchor cable

is 579 feet long.

Hauling such an enormous cable

in these tight spaces

calls for a compact
yet powerful piece of equipment.

So this is a jack that we use
to actually make the adjustment.

This is 150 ton ram.

We use this to either extend
the cable out a little bit

or bring the cable in
to maintain

a 65-ton average on the cable.

The jack begins to pull,

all with the press of a button.

You see the travel
of the cylinder right there.

We're actually very slowly
pulling the cable in.

Over here in the other room,

you can see we have this air gap
between the jacking plate

and the jacking head.

And so we're actually pulling
the cable into the pontoon.

So now we've gained
about an inch,

so we're gonna
put shims in here.

These steel plates
will bear the load

when the jack is released.

Right now, this time of year,

we only have to move it.
Probably an inch.

In the spring and the fall,
we'll move it about six inches.

Adjusting the 110
anchoring cables is crucial

for keeping the bridge
in alignment

and maintaining
a safe road surface

for more than
50 million vehicles every year.

So if we didn't
have these anchor cables,

eventually this bridge
would float north or south,

depending on which way
the wind's blowing.

Across a combined
bridge span of three miles,

these 38 jumbo pontoons
support a lifeline

for millions.

Without these
incredible floating bridges,

the city would be gridlocked.

The first stage of this
mega project is complete,

but engineers will face
more impossible challenges

in their mission
to create the world's first

floating railroad line.

As we transition
to a floating bridge,

it tends to move a little,

and this could
potentially disrail a train.

In Seattle,
an exploding population

has pushed the transportation
network to its breaking point.

In an attempt to defy
the impossible,

lake Washington's
colossal floating bridges

continue to evolve.

The next stage of the project
is to install

a one-of-a-kind railroad
across the north span.

Over 350 tons when fully laden,

the 55-mile-per-hour
commuter trains

will carry more than
18 million passengers

across the bridge every year.

Construction of this
groundbreaking project

is underway.

To my right is
the first set of tracks.

There'll be two sets
of tracks here

when the construction
is complete.

But these new tracks
create a unique danger

that engineer Craig Delalla
must overcome.

The rail system is powered

by a 1,500 volt D.C. System.

The return path for that current
is the rails here.

Water and electricity
famously don't make a good mix.

If electricity
escapes the tracks,

it could lead to disaster.

And surprisingly, the biggest
concern is not electrocution,

it's corrosion.

So any time
you have a steel structure,

the risk of rust or corrosion,

which is the loss of metal,
could impact the bridge.

By introducing rail
to the floating bridge,

it further increases the risk
of corrosion to the bridge

and the bridge structure.

When that current
discharges into the water,

it can corrode crucial
components at the exit point,

threatening
the bridge's integrity.

For this unprecedented
construction project,

Craig's team needed
to invent brand-new methods

to eliminate destructive
stray current.

So you'll see here that
there's multiple elements

of isolation,
including plastic pieces here

between the track
and the fastener.

We also coat the bridge with
a special dielectric material

that is also a high insulator
for electricity.

And so with these elements,

we are able
to protect the bridge

from any stray current ever
making its way onto the bridge.

But with this
mighty structure at stake,

the team isn't taking any risks.

Have to move
these barriers out of the way.

Should any stray current make it
through

the first line of defense...

This is gonna be harder.

...There is a backup plan.

The anode assembly is the one
without a tape here.

So we have here is the anode
coming out of the water.

There's eight of these that hang
50 feet down into the water.

These are mixed metal oxide
anode assemblies.

He's put current into the water,
which is drawn into the bridge

and allows the bridge
to polarize.

Left unchecked,

stray current
could enter the lake

through bridge metal,

but over 1,400 anodes

feed another electrical charge
into the water.

This protective flow drives
into the bridge structure

and holds the stray current
at bay,

saving crucial components.

Without corrosion control,

the life expectancy of
the bridge could be shortened.

Applying it to a floating bridge
like this

is really
something extraordinary.

With the danger
of corrosion eliminated,

the team can begin
to install the rail.

But now a new threat looms
over the project.

So right now, we're about
to go across the bridge.

Keeping the mission on track

is engineer john Sleavin.

As we transition
to a floating bridge,

we are on a floating structure,

and just like any marine vessel,

it tends to move a little.

Now, for an automobile
with rubber tires,

they can go across an angled
point or a bump quite easily.

And this is very difficult
for a train

because the steel rails
need to be continuous.

They can't have brake points
or angle points

that could
potentially disrail a train.

The floating bridge
needs to handle

a range of movement
caused by lake levels,

wind,
and uneven traffic loading.

This stretching
and twisting at the joints

constantly changes
the transition angle,

threatening a track misalignment
between lake and land.

For 800 passengers
on a speeding train

close to heavy traffic
and deep water,

this could be fatal.

We need to find a solution
across that expansion joint.

That's critical
to the operation of the rail.

To evade
a devastating derailment,

john's team will need to connect

with the innovators of the past.

In the pacific northwest,

engineers are designing
a floating railroad bridge

that will connect the two sides
of lake Washington,

but changing lake levels,
wind, and uneven traffic loads

can cause unwanted movement

and threaten the integrity
of the bridge.

To keep things running smoothly,

the team will need
to go back in time.

Norway... known
for its vast fjords.

Civil engineer
Berthe Dongmo-Engeland

is on the hunt for a relic

from the golden age
of locomotive travel.

Scottish engineer Thomas Bouch

encountered a similar problem

when extending Great Britain�s
railroad lines,

but in 1849, he came up
with a solution

that would roll out
across the continent...

The train ferry.

Wow, look at that.
This is so amazing.

Bouch's concept of
a ship with inset rails

enables locomotive wagons
to float across water.

This ferry in Norway
follows Bouch's design.

But the ferry itself
is only part of the story.

Once the wagons have reached
the end of the line on land,

there's still the problem
of getting them onto the barge.

A misalignment of the track
would be catastrophic.

And with lake water levels
constantly changing,

Bouch needed a clever solution.

The adaptability of Bouch's
hinged ramp is a concept

that will prove instrumental
for the team in Seattle.

With the help of
an enormous winch system,

the span is lowered and the
tracks are perfectly aligned.

Connecting these tracks
provided a lifeline

for the region's industry,
with an amazing roll-on,

roll-off solution.

The groundbreaking train ferry

and hinged ramp configuration
kept cargo wagons on the move

and changed locomotive
transportation forever.

170 years
after Bouch's inspired idea,

Seattle�s greatest engineering
minds have developed a system

that he could have
only dreamed of.

We call this a track bridge

because we're bridging
over that expansion joint.

This unique design
has to contend with conditions

not seen on any other
railroad bridge in the world.

We had looked
at some other systems,

but this has two more degrees
of motion

that don't exist
on other bridges.

What we have is a system
to try to handle

all those different
levels of movement,

but rather than happening
at one point on the rail,

we've spread that over
a longer distance.

As we go underneath here, we can
see some different elements.

Each of these wings
have a curve to them.

That means
when the bridge goes down

because the lake level
goes down,

these wings will rotate up.

And when the opposite happens,
these wings rotate down.

These curved wings
work in unison

with a complex range
of components

to bend the rails
into a gentle arc

and keep them level over
the moving angle points.

Eight of these 43-foot-long
track bridges

will cross the four hinges
between fixed

and floating segments,

allowing a smooth transition
for the trains.

After the complex
track bridges are assembled,

the system is thoroughly tested

at a special facility
in Colorado

to ensure safety,
speed, and efficiency.

Our tests revealed
that at our designed speed,

our maximum speed
of 55 miles an hour,

the track bridges were good.

The stresses
in the rails were fine,

and the ride for the passengers
was comfortable.

If we didn't have
this track bridge,

it probably would have been
impossible to put trains

across the bridge.
At the very least,

we would have had
to stop the trains

and almost just bounce
across it.

At its worst condition,

that may have even
caused the trains to derail

at that low speed.

With this incredible design,

Seattle�s engineers
are one step closer

to conquering
the seemingly impossible.

This is a completely
new and unique solution

addressed just
for this specific location.

Nowhere else in the world

are there any track bridges
like this.

But to realize their dreams

of crossing lake Washington
by train,

engineers face
one final challenge.

We'll have four-car trains,

so when two trains
are passing each other,

that puts a lot of stress
on the concrete.

And to create
more impossible engineering,

the team will have to turn
to innovators of the past.

Wow. I'm completely
awestruck by this building.

It really is impressive.

Seattle, Washington...

Home to the world's
only twin floating bridges.

And these superstructures

are about
to get another world first.

For the project's final phase,

the planet's only
floating railroad line

will cross an enormous 1.5
mile span over lake Washington,

revolutionizing Seattle�s
transportation network.

But these concrete bridges
will need

to support the weight
of multiple train cars.

We have thousands of daily
commuters that rely on this,

as well as sports fans
and university students.

Engineer john Sleavin
is in charge of the project.

So when these trains
are fully loaded,

we'll have four-car trains,

and each car
will weigh approximately

175,000 pounds.

So when two trains
are passing each other,

essentially doubling the load,
which is very heavy in one spot,

that puts a lot of stress
on the concrete.

A massive four-car
train at maximum capacity

could weigh 350 tons.

When two trains pass,
as much as 700 tons

could bear down on a short
stretch of the bridge.

This crushing load can put
enough stress on the concrete

to cause catastrophic ruptures.

We've done a lot
of structural analysis

on these loads

and realizing it takes
a lot of stress into the bridge,

and so to preserve the lifetime,

we need to figure out
how to strengthen the bridge.

So engineers will have
to reinforce

the concrete to withstand

the full force of hundreds
of daily train crossings.

It's a challenge
that might be impossible

without the innovators
of the past.

The city of Lourdes,
southern France...

An important holy site

for catholic pilgrims
from around the world.

Civil engineer Patric Nagle

is going underground
in search of a structure

with a capacity
for a colossal congregation.

Whoa.

This is the basilica
of st. Pius X.

I'm completely awestruck
by this building.

It really is impressive.

It's built beneath the city

to protect views
of the sacred site above ground.

What is striking about
this magnificent building

is a wide open space...
No central columns, no supports.

And we can see the structural
form of the 29 arches

running the length
of the building,

and this creates a usable space,

which can accommodate
25,000 people.

But this subterranean
structure seems to defy gravity.

The flatness of the arches
is maybe something

we wouldn't expect. A typical
arch is much more like this.

These are very flat arches.

It is clear
that something special here

is happening from
an engineering perspective.

This engineering enlightenment

came from Eug�ne Freyssinet.

In 1928, he perfected

a method
of concrete strengthening,

using strands of steel cable
under high tension.

This technique,
known as post tensioning,

provided support for concrete
beams of unprecedented spans.

But hidden within the concrete,

it's not easy to see
how this system works.

So here we have a simple model.

We have a number
of wooden blocks,

which represent a concrete beam,
resting on two supports.

And you will see a string
running through the beams,

which is simply there
to hold together the blocks.

If I apply a load to the beam,

you will see that
it is put into bending,

and you can see cracks
opening up within the concrete.

So the secret is to put
in compression

before the load is applied.

To achieve
the compression needed,

post tensioning must be
introduced into the beam.

So in this case,
it is provided by string

and a tourniquet
to tension the string.

So I have now tightened up
the stressing, if you like,

and we put this back
on the supports.

So this time, we can apply
double the load,

and we can see that there is
no movement and the beam

does not go into bending.

This gives a much more
efficient use of the concrete

and allows us
to provide bigger spans

and more efficient use
of the material.

By compressing the beam,

its density and strength
are increased,

a method that could prove vital
for Seattle�s bridge engineers.

So essentially what we are doing
in the beams

and the arches behind me here
is applying an external force

to increase the load-bearing
capacity of the structure.

The tendons that we see in here

are formed of steel strands

housed within ducts and stressed
by hydraulic jacks

after the concrete has hardened.

The strengthened
concrete provides

an expansive ceiling

without the need
for obstructive pillars.

Instead, arches span the chamber

and descend to the floor
close to the edge.

Looking at the structure today,

there are no cracks.
It is very finely designed

to make sure we maximize
the capacity of the concrete.

This long, shallow vault

would not have been possible

without Freyssinet's
extraordinary

post tensioning solution.

Without it, we would not be able

to achieve some of the beautiful

and brilliant structures
we see around us today.

Back at Seattle�s
floating bridges,

engineers are applying
Freyssinet's

groundbreaking technique
on a record-breaking scale.

For the final phase
of the I-90 floating bridges,

engineers are constructing
the planet's first

and only floating railway line

to cross the enormous 1.5-mile
span over lake Washington.

Just like at the basilica
of st. Pius X in France,

they're fortifying concrete
through extreme compression.

So what we've done
to strengthen the bridge

is put post tensioning cables
in the bridge.

But the super-sized
system on lake Washington

is using some of the longest

post tensioning cables
the world has ever seen.

These cables are
approximately 4,000 feet long,

running from one end
to the other.

One continuous cable
in each one of these conduits.

Very unique in this situation

that we've added 4,000 feet
of post tensioning.

Most post tensioning
is much shorter...

100 to maybe 200 feet.

With a combined length
of over 78,000 feet,

20 of these steel super cables

are thread through the pontoons,

spanning the north bridge's
floating platform.

Powerful hydraulic jacks
then pull them tight.

So what we've done is we've
put conduits through the bridge,

those conduits are then used to
string the cables through that,

and we pull those cables tight.

But keeping a post
tensioned mega cable in place

requires oversized anchors.

So here are the reaction frames
inside the bridge.

These are the big steel frames
that we pull tight against

when we tension
the post tensioning cables.

So their job is to hold
the post tensioning cables tight

so that we put that force into
the bridge to strengthen it.

20 massive reaction
frames weighing 7.5 tons each

are pulled inwards
by the tensioned cables.

Like huge bookends,
they squeeze the bridge

from either side.

Compressing the concrete
increases its density

and strengthens the bridge,

allowing it to take
an even heavier load.

Applying extreme compression
to the structure

has to be executed
with pinpoint precision

to within 1.5 millimeters.

These frames are critical.

Without them, there's no way

we could have added
post tensioning.

The result is
a super-strong floating platform

capable of withstanding
the 700-ton point load

of two trains
crossing simultaneously.

So this is an incredible
solution to the problem,

extremely long post tensioning
cables added to a bridge

allowing us to add the trains
to the surface of this bridge.

The I-90 floating
bridges represent

impossible engineering
on a staggering scale.

Every stage of this
groundbreaking enterprise

poses extraordinary challenges.

There are many facets
and many people

involved in this design,

and it's been really great
working on this.

I'm really proud
to see it coming together.

By building on the work

of the pioneers of the past,

overcoming huge challenges,

and pushing the boundaries
of innovation...

This is some of the most
incredible engineering

that I've ever seen.

It's extremely exciting
for me and my team

to be able to work on such
not only an important project,

but a unique project.

...The engineers
are succeeding

in making
the impossible possible.

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