Today on "Impossible engineering,"
the world's toughest structures.
The largest hydroelectric power station in the world.
And a football stadium of record-breaking proportions.
It's the longest continuous single arch span in the world
and, really, an incredible engineering feat.
It took revolutionary engineering
to make the impossible possible.
Captions by vitac... www.Vitac.Com
Captions paid for by Discovery communications
China, the world's most populous country.
At 1.3 billion people and rising,
the country's infrastructure is under immense pressure.
Living in downtown Shanghai, it's so easy to see
how much energy is consumed on a daily basis.
In this city alone, population has grown to 24 million people.
To sustain this many people,
the country consumes almost as much coal
as the rest of the world.
But China needs a more sustainable way
to keep the lights on.
Their solution... the three gorges dam,
the largest hydroelectric power station
in the world.
It's over 7,500 feet long,
that's 21 football fields,
and holds back a 400-square-mile reservoir.
Construction began on this incredibly tough structure 1994.
Getting the build right is a matter of life and death
for the millions of people
living further along the Yangtze river.
With millions of tons of water pushing against the wall,
the residents downstream
are really depending on this wall to stay up.
Any imperfections
and the consequences could be catastrophic.
A concrete structure of this magnitude
would be impossible without one of America's
greatest engineering achievements.
Wow.
This is the hoover dam.
At the time of its construction,
this was the world's largest concrete structure
that had ever been built.
Even today, roughly 80 years later,
it takes your breath away.
Weighing in at 6.6 million tons of concrete,
this was an unparalleled engineering marvel.
The dam harnesses the power
locked within the mighty Colorado river.
The dam stands 700 feet tall
and has a base thickness of 660 feet.
The biggest problem
and the biggest challenge was one of sheer scale.
But the severe southwest heat
makes building a structure as big as the hoover dam
extremely difficult.
If engineers poured all of the hoover dam's concrete
in one go, it would take 125 years
for it to cure and cool, meaning uneven setting
and potentially catastrophic cracking.
Hoover dam project supervisor
frank Crowe came up with an ingenious solution,
one that can still be seen deep within
the old inspection tunnels running through the dam.
The solution was to pass extremely cold water
through one-inch pipes.
The amazing thing is we can actually still see evidence
of those pipes here.
In 1931, thousands of workers began building the hoover dam
using gigantic blocks, cooling the concrete
with ice water produced by a refrigeration plant.
As an engineer, this is an incredible sight to see.
Over 80 years later, the hoover dam
still provides electricity to three states.
The three gorges dam is five times bigger
and generates an incredible 11 times more power
than the hoover dam.
Building it requires
almost a billion cubic feet of concrete.
In 1998, pouring begins.
To accelerate the curing process
and reduce the risks of cracking,
engineers take techniques pioneered at the hoover dam
to a whole new level.
The ingredients are air cooled before they're mixed.
High-speed conveyors take the concrete from mixing zone
to site in just 15 minutes.
Workers pour an average of 700,000 cubic feet every day.
Water cooling is supplemented
with a mist sprayed over the working area
to reduce the effects of the hot summer weather.
It takes eight years to pour all the concrete.
This massive structure harnesses
the clean hydroelectricity potential
of China's largest river, the Yangtze.
The Yangtze river is the third largest
and longest in the world.
And the river is now the lifeblood
for the thousands of people who live along it.
But blocking ship traffic on this busy waterway
with a giant dam is simply not an option.
To get the ships through,
the three gorges team are employing a technique
that dates back to medieval times.
The lock is almost a mile long.
It raises and lowers river traffic 370 feet
through five giant steps.
But there's a catch.
Taking four hours to pass through the locks
is simply too slow for most ships traveling down the river.
So Mr. Ding and his fellow engineers
must come up with another solution, and fast.
Tough enough to hold back the mighty Yangtze river,
the three gorges dam
is the largest hydroelectric power plant in the world.
But getting vessels through the dam's
massive ship locks quickly would have been impossible
without the pioneering engineers of the past.
In 1870, designer Edwin Clark was asked to solve
a particularly tricky problem
facing the small village of Anderton
in the north of England.
He was asked to link the busy Trent and Mersey canal
with the adjacent Weaver river to speed up journey times
for barges carrying valuable commercial cargos of salt.
This was a pretty stiff challenge for Clark
in the late 1800s because the height between the canal
and the river was about 50 feet.
So Clark developed an ingenious solution.
Known as the iron spider,
the Anderton is the oldest operating boat lift
in the world.
It's extraordinary.
It's a three-story-high marvel of Victorian engineering.
Clark's creation scoops up barges
and the water they're floating in,
transferring them in one smooth action.
At the time, this was revolutionary,
but the iron spider is based
on a fundamental principle of water pressure.
If you apply a pressure on a liquid in a closed system,
then that pressure is distributed
throughout the whole liquid in the system.
And Edwin Clark used this to great effect
with his boat lift at Anderton.
He started off by making two watertight caissons.
These are the tanks which held the boats
and the water in which they floated.
And he supported those caissons on top of two hydraulic rams,
and there was a liquid in those rams
and a pipe joining them both together.
So as I exert some additional force
to this hydraulic ram,
I can start to see
that the pressure is being pushed through
the adjoining pipe and lifting up my other hydraulic ram.
It's brilliant.
At the three gorges dam, designers are building
a ship lift similar to Edwin Clark's,
but on an epic scale.
It feels like I'm in a big, massive swimming pool,
and I'm being pulled up.
It's an engineering feat, a beauty in so many ways.
And super impressive.
The three gorges ship lift
can carry a 3,000-ton passenger liner.
Reinforced concrete towers
support the lift's 433-foot steel pool.
Instead of hydraulics,
the lift uses massive counterweights and pulleys
to raise the pool and vessels floating in it
a vertical distance of 370 feet.
This world record-breaking lift allows ships
to pass through the dam quickly and easily.
Stretching nearly a mile and a half
across the Yangtze river,
it holds back an almost 400-square-mile reservoir.
But excessive water can produce serious consequences.
Now, if we imagine a flood situation
where we have lots and lots and lots of water
flowing over this dam,
we've got all that water hitting the bottom of the dam.
As we can see here, the integrity of the dam
becomes very questionable and it starts to collapse.
Oh, there it goes.
To prevent this,
engineers had to look to the past for inspiration.
The Marèges dam in central France
is almost 300 feet tall.
Its builders feared overflowing water
would destroy the foundations,
eventually leading to its collapse.
To prevent this, engineer André Coyne
developed something novel.
This is a ski jump spillway,
so called because it has a lip at the bottom,
just like a ski jump.
And the ski jump prevents that water carrying
all the way down to the base of the dam,
where it can seriously erode the foundations.
It gets flicked into the air,
and all that water turns into droplets
as it's mixed with the air, and the energy is dissipated.
Coyne changed the way dams were designed forever.
The colossal three gorges dam
uses 46 ski jump spillways that push floodwaters 300 feet
away from the dam's foundations.
But how do engineers harness the power of the Yangtze river
to make the three gorges dam
the most productive hydroelectric power station
on earth?
The monumental three gorges dam
is the most productive hydroelectric power station
on the planet,
tough enough to harness the power of the Yangtze river.
This feat would have been impossible
without the engineers of the past.
Designers looked to the innovations
of 19th century engineer James B. Francis and his work
in the busy textile town of Lowell, Massachusetts.
The problem was that the mills here in Lowell
were being driven by simple water wheel systems.
These are relatively inefficient.
They're driven by water falling into the buckets
to make them turn,
only using a portion of the energy available
here in the canal system.
What Francis designed changed the world forever.
His original invention can still be found
deep within Lowell's canal complex.
Wow.
So this is it.
This is the site of the very first James Francis turbine.
This turbine, right here,
started the hydropower revolution.
James Francis took the idea of a waterwheel
and turned it on its side.
He enclosed the turbine,
so water was in constant contact with the wheel.
He added a series of vanes
to direct the water at the optimum angle.
The sum total of all those enhancements
lead to nearly 90% efficiencies of the turbine.
As the biggest hydroelectric project on earth,
the three gorges dam
uses the world's largest Francis turbines.
This is one of the two turbine buildings.
And just listen to that.
That is the sound of huge quantities of water
traveling at up to 80 miles per hour,
turning the 32 largest-ever Francis turbines built.
Installing the giant turbines
was an engineering feat in its own right.
Each turbine weights 450 tons.
The crane needed to install them
had to be factored in to the design of the dam.
These 450-ton turbines
can generate the equivalent electricity
of 25 million tons of crude oil
and, wait for it,
50 million tons of coal.
Water enters through a series of huge inlets
and falls 260 feet towards the Francis turbines.
With a flow rate of up to 33,000 cubic feet a second,
each turbine rotates at 75 revolutions a minute,
driving the generator above.
The potential for China is huge,
but the dam's location
is a daunting 600 miles away from Shanghai.
Engineers needed a system that would deliver that energy
huge distances with minimum losses.
And they wouldn't be able to do it
without one of history's most extraordinary inventors.
Engineering genius Nikola Tesla.
In 1895, the first large-scale generating plant in the world
housed is groundbreaking super-efficient transformer.
To demonstrate what a transformer does,
we have this simple race track set up here.
And I'm gonna start by supplying the same amount of voltage
to each track.
That's exactly what we expected,
a dead heat.
Now let's do the same experiment again,
but step up one track's voltage
with a transformer.
So now, let's race.
Sure enough, the stepped-up voltage produced a faster car.
A step-up transformer works
by sending power into a primary coil,
creating an alternating magnetic field.
When a secondary coil that has more windings on it
is placed beside it,
the alternating field is transferred
and, thanks to those extra windings,
creates an output with a higher voltage.
Instead of shooting cars down a track,
Tesla's transformers enabled the power company to shoot
electricity great distances across the country.
Engineers at the three gorges power station
are super-sizing Nikola Tesla's innovative ideas.
The three gorges power plant
will generate 84.6 billion kilowatts of power annually,
supplying nine provinces and two cities.
This incredibly tough dam produces more hydroelectricity
than any other facility on earth.
For engineer Qihua Ding, it represents the culmination
of a lifetime's dedication.
It's my whole life work, and I feel very proud of this.
I think the dam is amazing.
Harnessing the power of a totally different force...
Every day I walk around
and am just marveled by the feat that this building actually is.
...Is one of the toughest dome stadiums in the world.
The roof structure itself is equivalent
to the weight of 99 Boeing 777.
The Dallas cowboys is one of the most popular football teams
in the NFL.
In 2009, America's team wanted a new home.
The idea from the very beginning
was really to create the finest stadium of its kind
anywhere on the planet.
Architect Bryan Trubey
was asked to build the largest dome structure in the world.
The result is the tough structural masterpiece...
The epic AT&T stadium.
AT&T stadium can host a jaw-dropping 105,000 fans.
The massive structure is almost 1,300 feet long,
with the world's largest sliding-glass doors on each end.
The building’s spine is two of the longest unsupported arches
on the planet.
They support a state-of-the-art roof
that can be opened and closed at will.
But building a roof over a football stadium
is no easy feat.
The huge forces that come into play
to keep 104-million cubic feet column-free are enormous.
So how do you hold up
one of the largest single-span roofs in the world
without any supports?
The massive AT&T stadium can 105,000 fans.
But supporting its gigantic dome structure without columns
requires tough infrastructure.
The solution comes from
the 19th century Portuguese city of Porto.
In 1875, engineers were building a new rail line
between Lisbon and Porto.
But when they arrived here on the banks of the Douro river,
their progress ground to a halt.
At the time, a span of this size
was considered extremely challenging.
And so a bold and innovative new approach to bridge design
was required.
French engineer Gustave Eiffel
was up for the challenge.
Now for Bridges,
the arch is actually a really brilliant shape.
But it does have its limits.
And I can illustrate that using this piece of card.
If I place this card between two stones
that represent the bridge abutments
and I place a load on it,
it supports that load using compression.
And the compression flows down through the arch
and into the abutments.
But of course in a location like we have here
where we need a much larger span,
we have to increase the length of our span
and our arch becomes much more shallow.
And then the forces of tension start to take over.
And ask my structure is loaded you can see
that it struggles to support that load.
And this was precisely the problem that Eiffel faced
here at the Douro.
Luke is heading into the heart
of Gustave Eiffel's solution.
So here I am,
dangling halfway up of Eiffel's magnificent arch structure.
And I have to say, it's a real privilege
to be able to do this.
By making use of a simple system of triangles,
Eiffel was able to create a structure
that was both light and very strong and stable
and had a bigger span than ever before.
And it's a real marvel of engineering.
Simply genius.
So to understand how this truss system works,
we can make a simple comparison between two shapes
that are commonly found in engineering.
If we look first at the square,
you can see that if I push down on it,
it doesn't take long until that square deforms and collapses.
And that's because the square
lacks inherent stability and rigidity.
But you can see if I take this triangle
and I apply a vertical load to it,
you can see that it's able to take that load.
And that's because these two side elements
go into compression,
this bottom element goes into tension,
and there's equilibrium created
at the point where I'm applying the load.
By using this truss system of triangles,
Eiffel left his mark on engineering history
when his bridge spanned the greatest distance of its age.
Eiffel's experiences here ultimately provided him
with the engineering knowledge and techniques
to go on to create his most famous structure...
the Eiffel Tower.
The designers of AT&T stadium
are using Eiffel's innovative arch truss design
in record-breaking proportions.
The stadium's twin arches
soar over 300 feet above the playing field.
Each one weighs over 3,000 tons,
distributing 19 million pounds of thrust
into four colossal concrete abutments.
But designers need these arches to support yet something else.
One of the largest challenges that we had
is it's not natural for a retractable structure
to be on top of that.
It creates a very steep slope,
at the very steepest level,
you know, we're at a 23 degree angle
which is really the steepest retractable roof
that's ever been done.
How do you move an 837-ton roof panel
up and down such a step incline?
It's a task that would be impossible,
had it not been for a high-altitude innovation
150 years ago, businessman and avid hiker
Sylvester marsh devised an ingenious solution.
After getting trapped on mount Washington in a storm,
he decided to build a railroad
so tourists could visit the top of the mountain.
The basic problem marsh faced, of course,
is that this grade is simply too steep for a regular railway.
In a typical car,
the wheels would have spun without any friction,
and the train would have slid right back down the mountain.
To overcome the extreme gradient,
marsh built a train that can literally grip the track,
a system known as rack and pinion.
The pinion is a toothed cog wheel
positioned centrally on the underside of the railroad car.
The pinion engages with a rack
which lies between the track's running rails.
You can hear the pinion engaging into the rack,
providing that extra connection and the friction
that's needed to overcome this steep grade.
Marsh's design was an engineering marvel.
When it opened on July 3, 1869,
tourists flocked to take the train
and come up to the top of this mountain
and enjoy this incredible vista.
Engineers at AT&T stadium in Texas
are using marsh's rack-and-pinion system
on an epic scale...
a cutting-edge track guides 1,600-pound panels
up and down the stadium's steep inclined roof.
You can see the rack here
and then the gear pin here will interlock with this.
So it's an extremely robust connection
that very directly connects
the roof to the retractable portion.
The gigantic roof needs surprisingly little power
to open and close.
The retractable roof
is powered by a series of 7.5 horsepower motors.
Each side is powered by 64.
So it's roughly a corvette engine
pulling and pushing the roof as it moves along.
When combined with the world's largest sliding-glass doors,
this awesome structure offers a unique open-air experience.
When everything is open,
you really have almost an outdoor experience
that you would get in an outdoor venue.
I think that flexibility and that uniqueness
is what sets this stadium apart.
But when the doors and roof are closed,
keeping all 105,000 spectators comfortable
in the boiling summer months of Texas
is a huge engineering challenge.
There were two big influences...
the external heat
hitting the building and heating it up.
And you've got 80,000-plus fans generating heat.
You've got all the technology,
including video and sports lights.
All those things create a particular challenge.
So how do you keep such a vast stadium cool?
What you'll see as you look across the top
of the upper bowl are huge ducts.
Many of these ducts are about six feet in diameter.
So you can actually walk through the middle of them.
The system can throw out 11,000 tons of cooling capacity.
What they're doing is delivering a curtain of air
that washes down
over the surface of the seating bowl.
So we're really not air-conditioning
all 104-million cubic feet.
We're actually air-conditioning a zone about 10 to 12 feet tall.
This downward flow of cool air blankets spectators.
It remains in place because of its density.
Cold molecules are packed close together,
increasing their weight.
Low-density hot air rises,
accumulating in the vast space in the dome roof.
The size of the interior
is one of our key physical properties
that allows us to separate the cooled air from the heated air
and keep the seating bowl cool.
But to truly be a multi-use venue,
engineers need a surface that can suit a variety of needs,
not just football.
We knew that it needed to be a venue
that would not just house the Dallas cowboys.
We wanted to be able to be flexible
so that we could move our field out to grass
or grass to concrete or concrete to wood.
To transform the stadium,
engineers must seek inspiration
from a structural masterpiece of the past.
The epic AT&T stadium is one of the toughest
dome structures in the world.
But to transform this football stadium
into a multi-use venue, engineers must look tot he past.
Developer Roy Hofheinz built an indoor baseball stadium
that could comfortably house the Houston Astros
away from the glare of the Texan sun.
It was the world's largest indoor arena
with a circumference of nearly half a mile.
At 350,000 square feet,
it made it the largest air-conditioned room on earth.
But a significant problem emerged when it opened.
Players used to complain
that the Lucite in the dome roof would reflect light,
making it virtually impossible
for them to catch a flyball.
Some of the panels were painted white.
But then that led to another problem.
The stadium grass started turning brown
and eventually died.
The stadium needed a solution fast.
Two American engineers, James Faria and Robert Wright,
had the answer.
The pair developed chemgrass... a synthetic turf
consisting of a carpet of nylon grass blades
stretched across a thin rubber base.
And in 1966, the Houston Astros
played their first ballgame on a fully artificial field
that, in honor of the stadium, it was renamed to astroturf.
Its portability allowed the astrodome
to host anything from basketball to racing.
Astroturf changed sports architecture around the world.
And the astrodome provided the blueprint
for an indoor, multi-purpose venue.
We have this surface for the Dallas cowboys.
We have a completely different field for college football.
We've had grass in here for soccer.
And we have had basketball here, as well.
I certainly think the multi-use aspect of it
will be one of the legacies of the stadium.
AT&T stadium can house over 105,000 spectators.
But to fill all those seats,
the stadium needs an unrivaled viewing experience.
You can set up one of the finest TV, surround-sound,
high-tech environments in your own house.
So what we had to do here was be better than that.
How do you make every seat the best seat in the house?
Watching sports on television at home
is a national pastime.
But to compete with that experience,
the engineers of AT&T stadium
had to develop an unrivaled viewing experience.
The ability to record a moving image onto film
was achieved by the late 1800s.
But transmitting an image
so it can be viewed in another location
is a much greater challenge.
Russian engineer Vladimir Zworykin
provided a starting point in 1931.
He patented a camera tube known as the iconoscope.
Within the tube, a captured image
was projected onto a mosaic of light-sensitive material,
breaking it into thousands of picture elements
known as pixels.
A sweeping electron beam charged the pixels
before they were fed out of the camera.
Zworykin's invention allowed us to turn a picture
into an electrical signal.
But it was how that moving image was transmitted
and then replicated on a screen at the other end
that's the really incredible part.
The emitron was the British broadcasting company's
first industry-standard camera.
By 1937, it was possible
to broadcast live into people's homes.
It was here at Wimbledon
that the BBC's first live broadcast of a sporting event
would take place
with the men's final being beamed into homes across London.
And the hefty young man from across the Atlantic
defeated the good-looking continental 6-3, 6-4, 6-2.
The key to transmitting a television picture
is in how the images are extracted from the camera.
So imagine this is a single still image
of a tennis champion.
It's a bit hard to believe in this case, I know.
What happens is that, inside the camera,
that image is scanned into individual lines.
Broken down like this.
And then these lines are taken out of the camera,
up to the transmitter...
Transmitted through radio waves
which are picked up by the aerial on top of your home.
Then they're brought down to your television
where these lines are reassembled again
into a full image.
And obviously, this has to happen very quickly.
But that's just a single frame.
To create a moving image,
TVs need to do this at least 24 times every second,
fast enough for the image to appear to be moving.
This illusion of movement is much the same
as you get with a flick book.
It's by looking at a number of still images
in very quick succession,
you get the illusion of movement.
Transmitted from London
through Alexandra palace's television tower,
broadcasts like the Wimbledon final
marked the arrival of one of history's greatest innovations.
Engineers in Texas are redefining live broadcast,
using one of the world's largest video boards.
It doesn't matter where your seat is.
You are a part of the action,
that you can see the passion and the inspiration
on the participants' faces.
These monumental arches
are once again providing a critical engineering solution
for this extraordinary building.
When we were all out here
and they hoisted that board up,
that's such a feat to marvel over
and to appreciate
just how complicated the engineering was.
Three... Two... One.
Since opening its doors in 2009,
AT&T stadium has hosted over 10 million visitors.
By learning from the great pioneers of the past,
adapting, upscaling, and making innovations of their own,
the engineers of the three gorges dam
and AT&T stadium have created
some of the toughest structures on the planet.
This venue proves
that if you have huge aspirational goals,
you can actually attain something
that's never been attained before.
They have made the impossible possible.