Original subtitles

Today on Impossible Engineering, a football stadium of record -breaking

proportions.

Every day I walk around and I'm just marveled by the feat that this building

actually is.

One of the largest dome structures in the world.

It's the longest continuous single arch span in the world and really an

incredible engineering feat.

It took revolutionary engineering. The roof structure itself.

is equivalent to the weight of 99 Boeing 777s. To make the

impossible possible.

The Dallas Cowboys is one of the most popular football teams in the NFL,

them the nickname America's Team.

And in 2009, America's Team decided it was time for a new home.

The idea from the very beginning was really to create the finest stadium of

kind anywhere on the planet.

Architect Brian Truby was asked to build the largest dome structure in the

world.

The engineering in the project was for us a particularly unique challenge.

What Brian created is a 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 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 this $1 .2 billion stadium is much more than a football field.

We knew from the beginning that the Dallas Cowboys would only be here 10

year. So we needed to make sure that this building would be alive and living

the remainder of the year.

Texas summers are brutal.

The stadium's 104 million cubic feet of interior space needs to be cool and

comfortable year -round.

The first step towards achieving this? A gigantic roof.

The roof structure itself.

is equivalent to the weight of 99 Boeing 777s.

Building a roof over a football stadium is no easy feat.

One of the incredible challenges with this venue is creating that large column

of free space.

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 support?

Since the dawn of time, engineers have struggled to hold things up.

The Temple of Artemis was one of the seven wonders of the ancient world.

But its vast roof needed over 100 columns to

stop it from caving in.

The Romans took a lightweight approach. The Colosseum's huge ring of awnings

protected spectators.

But sadly, not those that are staying.

The solution for AT &T Stadium 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

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, the challenges that Eiffel faced in building this span were just immense.

In addition to the width of the span, the river is also very fast flowing.

up to 20 meters deep in flood season, and this meant that it was impossible to

put piers in the water.

With no obvious way to support the bridge, Eiffel proposed an audacious

solution. An enormous single arch built into the sides of the riverbank.

An arch on this scale seemed an impossible task.

But Eiffel proved everyone wrong.

And this is the result of his achievement.

Isn't it an exquisite example of engineering?

In order to make this a reality, however, Eiffel had to completely

design.

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 as 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 Gustav Eiffel's solution.

So here I am dangling halfway up of Eiffel's magnificent arch structure. And

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

equilibrium created at the point where I'm applying the load.

By exploiting simple physics.

Eiffel left his mark on engineering history when his bridge spanned the

distance of its age.

Eiffel's experiences here ultimately provided him with the engineering

and technique to go on to create his most famous structure, the Eiffel Tower.

Not only that, but in creating this, he helped to completely redefine arch

construction. And today, arches form critical parts of some of the most

impressive and iconic structures all around the world.

The designers of AT &T Stadium are using Eiffel's innovative arch truss design

in record -breaking proportions.

It's the longest continuous single arch span in the world.

So we're really taking inspiration from some of the bridge structures that are

out there and applying it to the building.

So what you're looking at are two primary arches.

that span about 1 ,400 feet each. The size of the trusses themselves, they're

about 14 feet wide by about 35 feet tall.

The weather in Texas is beautiful during football season, so the owners want one

of the largest dome roofs in the world to also be retractable.

It's not natural for a retractable structure to be on top of that. It

very steep slope.

A seemingly impossible challenge.

In Arlington, Texas, engineers have created one of the largest sports and

entertainment venues on earth.

For architect Brian Truby, the stadium has changed the face of arena design.

From an engineering standpoint, there's really very few structures like this.

What you see here really is the most transparent stadium in the world. And

can see the arches, for instance, that span the entire length of the building,

about a quarter mile.

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

four colossal concrete abutments.

The concrete abutment then, what you see above ground, takes all those forces

directly into a large concrete footing below ground. It's about four times

larger than what you see above ground.

Each concrete abutment requires over 350 ,000 cubic feet of concrete.

Work began on the stadium's massive dome roof in July 2007.

They basically would start at the abutments on each end, and they would

with a single truss, and they would build towards the center.

Six shoring towers are erected to temporarily support each truss section

they're moved into position.

When the connecting keystone piece is added, not even a single column is

to support the stadium's dome roof.

Placing that keystone piece in the truss, that's really the first time

that that the structure's allowed to load on itself.

With the steel truss arches in place, engineers can begin work on the

massive dome roof.

So the roof itself actually covers about 660 ,000 square feet. And

the reason for the shape of the roof tracks back to Texas Stadium.

Texas Stadium is the former home of the Dallas Cowboys.

It's renowned for its open roof design.

The iconic hole in the roof is very signature to us.

The owners of the new stadium want to incorporate that same open design

but with the ability to close the roof in bad weather, a seemingly impossible

challenge.

One of the largest challenges that we had is that arch shape of the roof

structure below.

It's not natural for a retractable structure to be on top of that. It

very steep slope, particularly when you get to the ends.

At the very steepest level, 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 steep incline?

It's a task that would be impossible had it not been for a high -altitude

innovation made over 150 years ago.

Architectural historian Jen Massengarb is in the White Mountain National Forest

in New Hampshire.

She's looking for an invention many believed couldn't be built.

With an elevation of 6 ,288 feet above sea level, more than 1 ,900 meters,

Mount Washington has long been the site of exploration since the late 18th

century. But it's got bad weather and rough terrain and an incredibly steep

grade, and so only the most adventurous climbers were able to make it to the

summit to see the stunning views.

Sylvester Marsh was a successful businessman in the meatpacking industry.

But it was his passion for hiking that led him to his biggest achievement.

After getting trapped on Mount Washington in a storm, he decided to

railroad so tourists could visit the top of the mountain.

The basic problem Marsh faced, of course, is that this grade is simply too

for a regular railway.

In a typical car, the wheels would have spawned 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.

When it opened in 1869, the Mount Washington Cog Railway was an

marvel of its day.

It travels a total of about three miles, 2 ,700 feet at the base, and we're

headed up there, 6 ,288 feet above sea level, making it the second steepest

mountain cog railway anywhere in the world.

The secret to how it works lies in an incredibly effective system known as

and pinion.

Here's a simple demonstration about how this rack and pinion system works.

If we imagine for a moment that this plank of wood is the side of the

and I'm the train, I'm obviously going to try to get up the mountain, and you

can see that I slide back down.

However, if we apply a rack to the side of the mountain,

And I'm still the train. My feet act as these pinions in the rack. And you can

see that I can easily climb off the side.

The pinion is a toothed cogwheel positioned centrally on the underside of

railroad car.

The pinion engages with a rack, which lies between the track's running rails.

You can hear the pinion. and engaging into the rack, providing that extra

connection and the friction that's needed to overcome this steep grade.

And in fact, we're now on the steepest part of the track, called Jacob Bladder.

There's a whopping 37 % grade here. And in fact, the difference in height

between the front of this carriage and the back of this carriage is about 13

feet.

Marsh's engineering genius didn't end there.

To safeguard the train from rolling backwards, the pinion engages with a

brake so the cog can only move in one direction.

If the train starts to slide down the mountain, the ratchet will automatically

drop, locking the wheel in place.

Marsha'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.

And in fact, Marsh's design became the blueprint for other Cog Mountain

across Europe and around the world.

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.

One of the challenges with a retractable roof on a domed surface is, of course,

the curvature.

So each of the panels, as they move then down the tracks, they travel about 100

feet vertically.

Over 1 ,300 feet of mechanized railing is installed on the stadium's arches.

The amount of engineering that went into this was really massive.

You know, you have structural electrical mechanization.

The 65 ,000 square foot retractable roof panels move using this rack and pinion

system.

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.

The motors need to generate almost 1 ,000 horsepower to close the roof.

To open the roof, the motors act as a braking system.

There's a lot of energy generated as they move back down because of the

of the panels themselves.

When combined with the world's largest lighting 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 the stadium

But to keep such an open venue comfortable in this sweltering Texas

stadium needs a supersized climate control system.

80 ,000 -plus fans generating heat. You've got all the technology, including

video and sports lights. All those things create a particular challenge.

In Arlington, Texas, engineers have created a modern marvel.

This building is about 3 million square feet.

The largest stadium built to date is about 2 million square feet, so we're a

third larger.

With a gigantic retractable roof and the world's largest sliding glass doors,

the structure literally embraces the element.

But to succeed as a year -round venue, the stadium needs a cutting -edge

control system.

We really felt like our fans deserved a venue that would be able to be climate

controlled, and mainly for the heat, because it gets really hot down here in

Texas.

Keeping all 105 ,000 spectators comfortable is a huge engineering

There were two big influences.

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?

Designers look to the great innovators of the past for the answer.

Man has strived to keep cool for centuries.

Roman Emperor Various Avitus demanded mountain snow be brought to his garden

during the summer to make the most of the natural breezes.

But his comfort was short -lived.

In 2nd century China, inventor Ding Wan created a mechanical fan system to

provide the perfect temperature for a room full of people.

Except that is for the unfortunate operator.

In the early 20th century, a problem facing the print industry inspired what

would become the first air conditioner.

In 1901, a young engineer called Willis Carrier was summoned to a publishing

company with a problem.

Because the facts had printed in colour, the paper had to go through the presses

multiple times to build up those different layers of ink.

But because of the heat and the humidity, the paper would swell and

time it was put through, and that would mean the colours ended up not being

aligned, ruining the print.

25 -year -old Willis Carrier had a simple but very effective solution.

Physicist Andrew Steele is heading into an artificial jungle to put Carrier's

concept to the test.

Now, it's not especially hot in here, but it's very humid, above 90%.

Here we have a modern reimagining of Carrier's invention.

We've got a nice big fan here on the back, and on the front we've got this

spiral of copper tubing.

So what we're going to do is pump some cold water through that copper tube.

We're going to suck the hot, humid air from all around us in through the back

the fan.

And as if it wasn't enough of a challenge taking on the jungle, we've

this kettle back here, which, when it starts to boil, is going to produce a

of steam.

Down here we have our reservoir of nice cold water. It's full of ice packs.

And inside here we've got the pump.

So what I'm going to do is just start the pump up.

And over here, just switch on the fan.

And you can see this hot, steamy, humid air is being sucked through the fan.

As the water vapor in the humid air hits the cold pipes, it condenses, turning

it into a liquid state.

And even though it's only been on a very short period of time, it's already

sucked all this water, this humidity, out of the air.

Willis Carrier's method to reduce humidity at the publishing company had a

welcome side effect.

And on this side, it's actually quite pleasant. It's lovely, it's cool, and

very dry.

The modern air conditioner was born.

Factories and hospitals were transformed by this technology.

And in 1922, the advent of a centrifugal chiller allowed entire buildings and

department stores to enjoy the comfort of Carrier's invention.

Today, air conditioning units are completely ubiquitous.

They allow us to control ventilation, to clean air, to dehumidify, and most

importantly, to control its temperature.

Willis Carrier's invention truly has made the impossible possible.

Engineers in Texas are using Carrier's groundbreaking invention on a staggering

scale.

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, but that's not

enough. To keep spectators comfortable in this vast open space, designers will

need to take advantage of the laws of physics.

is one of the largest dome structures in the world.

It truly is a one -of -a -kind venue and really an incredible engineering feat.

Keeping all 105 ,000 spectators comfortable is no easy feat. To get the

done, engineers are taking advantage of the laws of physics.

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

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

to grass or grass to concrete or concrete to wood.

Engineers are seeking inspiration from a structural masterpiece of the past.

Civil engineer Alfred Castillo, Jr.

is exploring an engineering icon that's been closed to the public almost 10

years.

Wow. This is incredible.

Opened in 1965, the Houston Astrodome redefined sports architecture.

Prior to the Astrodome, stadiums here in Texas, they were built completely open

to the elements.

But coming to a baseball game in the middle of a Texan summer isn't exactly a

great deal of fun.

Developer Roy Hoffines was moved to build a stadium after his young daughter

complained of the heat and mosquitoes when they attended baseball games

together.

The result was a $35 million 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.

A small but significant problem was discovered when it opened.

Players used to complain that the lucite in the dome roof would reflect light,

and therefore making it virtually impossible for them to catch a fly ball.

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

grass blades stretched across a thin rubber base.

After a trial at a Rhode Island school, the innovative product was rolled out at

the Astrodome.

And in 1966, the Houston Astros played their first ballgame on a fully

artificial field that, in honor of the stadium, it was renamed AstroTurf.

This ingenious invention provided a resilient playing surface for nearly 40

years. Its portability allowed the Astrodome to host anything from

racing.

AstroTurf changed sports architecture around the world.

And the Astrodome provided the blueprint for an indoor multi -purpose venue.

You can fit three Astrodomes inside Arlington's mighty stadium.

You know, it's about 120 ,000 square feet of surface area, and it's really

stage.

What you see here is the result of 30 or 40 years of technological advance and

creates really the finest playing surface.

To make the stadium's football field, The massive concrete substructure

over 100 ,000 square feet of state -of -the -art synthetic turf.

Synthetic turf really rolls up just like Carthage,

rolls back out, takes about 10 hours.

We've had 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.

But to create a venue that will truly leave its mark on history, engineers

turn to a great innovation from the past.

It was here, at Wimbledon, that the BBC's first live broadcast of a sporting

event would take place.

And install one of the largest video boards.

AT &T Stadium is an engineering marvel, one of the largest dome structures in

the world. It can house over 105 ,000 spectators.

This building has really changed the way these buildings are perceived.

But to fill all those seats, the stadium needs an unrivaled viewing experience.

For us, our biggest competition is not the team on the other side of the ball.

It's network television.

You can set up one of the finest TV surround sound high -tech environments

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?

It would be impossible without one of the 20th century's greatest innovations.

London's Alexandra Palace, an iconic building that was at one time the center

an engineering phenomenon.

At the beginning of the 1930s, the race was on amongst some of the world's

finest minds to develop the first universal, standardized broadcast

system.

Scotsman John Logie Baird had already created a mechanical method of

transmitting a moving image.

And in the U .S., Philo Farnsworth had developed a rudimentary electronic

version.

Engineers were determined to build on those pioneering inventions.

Leading the charge in the UK was a team of British scientists led by the Russian

Isaac Schoenberg.

Hard at work here at Alexandra Palace.

At the same time broadcast television was being developed, engineers were

building the very first cameras.

The basis for recording any image is capturing light.

And what we've got here is a simple model of a camera. So we've got a big

box and we've got this hole in the front. Let's go around and have a look,

what we can see.

Well, actually, right now, not very much because that hole is so big that all

the light is bouncing off the objects in front of the camera, not really ending

up anywhere in particular on the screen. We've just got a wash of light.

So what we need then is a lens. And as our lens, I'm going to be using this

magnifying glass. So if now we pop that.

There we go, on the front of the camera.

I can actually bring the scene in front of the camera into focus.

The ability to record a moving image onto film was achieved by the late

but transmitting an image so it can be viewed in another location is a much

greater challenge.

Russian engineer Vladimir Zvordkin 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.

Zvorkin'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

the other end that's the really incredible part.

Schoenberg's team built on Zvorkin's technology, creating the Emetron, 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

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 into your television, where these lines are

reassembled again into a full image.

And obviously, this has to happen very quickly.

Oh, there we go.

Schoenberg's Emetron camera system used 405 lines, what was then considered high

definition.

I'm not sure I can manage that many.

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.

The illusion of movement is much the same as you get with a flick book.

By looking at a number of still images in very quick succession, you get the

illusion of movement.

Transmitted through Alexandra Palace's television tower.

Broadcast like the Wimbledon final marked the arrival of one of history's

greatest innovation.

It's hard to imagine the modern world without television.

From transmitting breaking news around the world to covering major sporting

events, TV is now central to the way we communicate and are entertained.

And without it, the world would be a very different place.

Engineers in Texas are redefining live broadcast using one of the largest video

boards.

There's about 10 .5 million LEDs. That's about 26 ,000 square

feet of video surface.

It's really unparalleled in major stadia.

It doesn't matter where your seat is. There is always an unbelievable view.

You don't feel like you are in the upper deck. You feel like you are a part of

the action, that you can see the passion and the inspiration on the

participants' faces.

The Colossal Television poses an enormous challenge for engineer Guy

The structure is 72 feet tall and 160 feet wide.

That's 1 .3 million pounds.

That's a weight of 40 airplanes.

It's so massive, it has to be suspended from the building's main arch trusses.

So here we are on basically level 10 of the video board.

We're about 170 feet off of the ground.

We have the main arch trusses, which are spanning the nearly quarter -mile span.

And then we have these box trusses, which are there to provide support to

video board.

These monumental arches are once again providing a critical engineering

for this extraordinary building.

When we were all out here and they hoisted that board up, everyone was

at the roof wondering, did it sag?

That's such a feat to marvel over and to appreciate just how complicated the

engineering was.

Three, two.

Since opening its doors in 2009, AT &T Stadium has hosted over 10 million

visitors.

The first thing people do when they walk in, they walk in and they go, oh wow.

It's really fun to watch people's reactions.

For architect Brian Truby, it's been a life -changing experience.

Seeing the building perform.

is one of the most gratifying things in my career.

By learning from the great pioneers of the past, adapting, upscaling, and

innovations of their own, engineers have changed the face of stadium design.

This venue proves that if you have huge aspirational goals, you can actually

attain something that's never been attained before.

and have made the seemingly impossible possible.

You know, every day I walk around and I'm just marveled by the feat that this

building actually is.

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