From the sands of the Arabian Desert rises the tallest man-made structure on Earth, a city in the sky nearly half a kilometer tall.

The Burj Dubai is the pinnacle of skyscraper engineering. It owes its success to seven key inventions. We have lined up seven landmark buildings, historic giants of the skyscraper world.

At the heart of each one lies a major technological innovation that allowed engineers to reach ever taller into the sky.

One by one, traveling up the scale, we'll reveal the incredible stories behind these structures and the inventions that have driven them higher.

Seven ingenious leaps forward that have enabled skyscrapers to evolve big to bigger into the world's biggest.

Dubai is the fastest growing city in the world. An army of cranes and laborers work around the clock to turn the city into a place that the whole world will look up to.

The centerpiece in the grand plan is the Burj Dubai, tallest skyscraper in the world.

It is the ultimate leap in a series of historic engineering breakthroughs. We need to go back in time and look at how skyscrapers began.

The first breakthrough happens in the 19th century with a building that's only 43 meters tall. The builders of the Equitable Life Building in New York realize that before buildings can reach taller, they must find a way to make people climb higher.

The first big obstacle to skyscrapers is the stair.

People weren't willing to walk up lots of flights of stairs. Stairs in old office buildings were long, they were very dark, and people weren't willing to climb stairs more than to the second floor or the third floor.

And if you were a lawyer and you were looking for clients, and you were on the fifth floor, you were undoubtedly going to lose clients because they didn't want to come up to your office.

By the time you reached the sixth floor, seventh floor, you're incredibly winded.

Ah, that's it for me. There's an obvious solution to the problem: the elevator.

But early elevators have one deadly fault: nothing stops them from falling if the rope breaks.

Yeah, but then a mechanic from Vermont invents a device that can stop a falling elevator almost instantly. In 1854, Elisha Graves Otis demonstrates his invention at the World's Fair in New York.

He stands on a platform high up in the air, apparently held only by a rope.

All right, Stan, be gentle with me. Then Otis tells his gasping audience that the rope is about to be cut. Stan, cut the rope!

And at the end of that cutting of the rope, he reportedly took off his top hat, bowed to the audience and said, "All safe, gentlemen, all safe." This is the world's first fully automated safety elevator.

It's a simple yet very clever invention. The critical element, the elevator rope, is secured with a powerful wagon spring mounted on top of the cab.

This spring connects to a set of metal prongs on each side of the elevator.

Prongs run along guide rails fitted with a row of teeth. When the rope breaks, it triggers a chain of events. The spring relaxes and forces the metal prongs into the teeth, locking the cab in place.

This is a true engineering breakthrough, a fact lost on Elisha Otis. He was not a businessman, he was not a marketer.

He was a mechanic, he was a tinkerer, and I don't know that he fully recognized the power of this invention.

The elevator completely transforms the urban landscape, and it all starts on a busy street corner in downtown New York.

the company's headquarters, a building of extraordinary significance because it was the first office building with an elevator. And without an elevator, the skyscraper would be impossible.

The building standing here today is the new Equitable Life headquarters. It has replaced the old Equitable Life building, which was not a skyscraper as we know it.

It didn't scrape the sky, it didn't soar up, but it changed the notion of what an office building could be.

Until the Equitable Life, the lower floors of a building are the most desirable, but the elevator completely reverses the economics of real estate.

Equitable understood that the upper floors now, which received light and air and were away from the noise of traffic, would be the most valuable spaces in the building.

So what did they do? They occupied the lowest stories in the building, and they rented out at the highest rents possible, the upper floors of the building.

So it's the whole idea of a skyscraper with high rents and views and light and air on the upper floors, which we still deal with today, that was invented at the Equitable building.

Dubai takes the idea of the elevator to the extreme.

Equitable Life had seven and a half stories. The Burj Dubai has over 160, a height that stretches elevated technology to its absolute limit.

The Burj Dubai will be able to accommodate 35,000 people. Getting a population the size of a small town in and out of the building is the ultimate challenge for the elevators.

To cope with the numbers, the Burj Dubai has 53 different elevators.

Some reach over 35 kilometers an hour and climb 120 floors in under 50 seconds.

The biggest lifts carry up to 46 passengers. Stopping such a speeding juggernaut in an emergency is a titanic challenge.

We're now talking 30 tons, 40 tons, 50 tons of moving mass. What happens to an elevator brake system is the equivalent of driving an 18-wheel truck off a cliff and stopping it in midair.

As soon as an elevator on the Burj Dubai exceeds its speed limit, emergency brakes spring into action.

Metal brake shoes bite down on the guide rails and generate enough braking power to stop the elevator within a few meters.

But at the end of the day, the safety that we depend on, that the riders depend on to bring the car to a safe and a controlled stop, is still a mechanical device.

The safety elevator allows the skyscraper to break through the five-story barrier. Suddenly, tall buildings are big business.

But as they approach 80 meters, traditional building materials are no longer strong enough. To make the leap to the 87-meter Fuller Flatiron Building in New York, the skyscraper must be reinvented.

This is the Monadnock Building in Chicago, a living fossil in the skyscraper world.

When it opened in 1893, it's the world's largest office block, but its 16 stories stretched stone to the limit.

The walls at the bottom must be a whopping two meters thick to bear the weight of the Monadnock.

the structure is so extremely heavy that it begins to sink into the soft Chicago soil. Eventually, half a meter of bricks and mortar disappear underground.

Obviously, stone is not skyscraper material. So when the architect of the Monadnock, Daniel Burnham, plans the Fuller Building in New York, he's in a bit of a pickle.

The extremely narrow plot dictates that his 22-story skyscraper has a triangular Burnham knows that there is no room for stone walls.

They would have to be so thick that there would be hardly any space left on the ground floor, and wasting valuable space is a cardinal sin for a skyscraper architect.

But if you look at the Fuller Flatiron today, it looks like it's built from stone. So how did Burnham do it? It's all just a facade.

Under the skin of the Fuller lies one of the most important building technologies ever invented. Burnham makes the building out of steel columns and steel beams locked together into a steel skeleton.

Steel is much stronger than stone, so this skeleton can be thin and light, yet it can support the weight of the whole structure.

To keep the weather out, Burnham can simply hang thin masonry walls off the steel frame like curtains. The building is an immediate success.

The Flatiron Building was the first skyscraper to become a symbol of New York. It attracted photographers, famous painters painted the building, and it became a symbol at the highest levels of culture.

The Flatiron even affects the weather. The shape of the building caused a wind tunnel effect, and men used to hang out at the corner and watch for women's dresses to blow up so that they could get a look at women's ankles.

Steel construction truly moves the skyscraper.

This is a new breed of building. Once the steel skeleton frame is perfected, basically you could build hypothetically to any height. And that meant that land values in commercial areas of New York absolutely skyrocketed because no longer was land valued for an 8 or 10 or 12-story building, which was the most you could build without the steel skeleton frame.

But now, the sky was literally the limit. The skeleton of the Burj Dubai combines the best of steel and stone.

It uses over 30,000 tons of steel, but in a very clever way.

Steel is embedded in artificial stone concrete. This reinforced concrete backbone will be clad in a high-tech curtain wall of glass and steel.

The wall latches onto the Burj Dubai in units of up to two stories tall. The panels themselves are rigid, but the joints between them are flexible.

If an occupant moves a heavy piece of furniture towards the edge of the skyscraper, the floor will bend and force down the exterior wall.

But the flexible joint in between the wall panels absorbs the movement, so the wall as a whole is not damaged.

The joints also allow each wall section to expand and contract as the desert sun passes around the skyscraper, heating it up.

But the most potent force it must withstand is the desert wind. The curtain wall of the Burj Dubai will cost a hundred million dollars. So before it's bolted on, the engineers take prototype sections for a test drive.

This is where the rubber meets the road. Yes, it has to perform. It has to perform right here today.

The engineers apply the ultimate test. An aircraft engine simulates a desert storm. We try to put everything that Mother nature would throw at the building.

In these tests, if the brackets can't resist the wind loads, you have the prospect of the whole curtain wall peeling off the whole building.

If you erected a curtain wall and you didn't find out about an inherent design flaw, like a leak or something, until after it was occupied and the first storm came, it's unthinkable.

The propeller spits wind and rain backwards at the curtain wall section mounted behind it. It reaches speeds of 75 kilometers an hour.

A real challenge for the curtain wall. Will the prototype withstand fresh air? The buffeting and the movement of the water across the surface is finding weaknesses.

And if there's any flaws in connections or holes in the curtain wall, the water will seep through. So if you see any water coming through, it's a fail.

And you know what's happened. But today, the prototype passes the test with flying colors.

The Burj Dubai takes one step further to completion. Now the challenge for the engineers is to stop the baking desert sun from turning their beautiful glass tower into a giant oven.

Steel catapults skyscrapers to unseen heights. As walls now no longer have to bear all the weight, architects can make them out of completely new materials.

Glass promises to flood buildings with light, but also with heat. To beat this new enemy, skyscrapers would need to get cooler.

When the United Nations designed their new headquarters in New York, they faced a dilemma. They want to cover the building with glass to make the interior as bright as possible.

What they don't want is a 39-story greenhouse. A glass wall would allow a lot of light into the building, but also solar radiation.

This would be absorbed by the objects inside. These, in turn, would radiate heat into the surrounding air and warm it up.

as the sealed glass windows can't let the hot air escape, things would get uncomfortable very quickly, even in the summer. So you need to have artificial cooling in order to make these glass skyscrapers work.

An American engineer called Willis Carrier cracks the cooling problem. He invents a machine that can cool and dry hot, moist air by making it wet first.

It injects a fine mist of cold water into a chamber. Next, it sucks hot, soggy air into this cold mist.

Seen up close, something remarkable happens. As the hot air hits the surface of the cold water, the air cools down and releases its moisture onto the droplets.

So the air is cooled and dried in a single step. Carrier's invention is the perfect solution to the heat problem in the UN building, but scaling it up to skyscraper size is a challenge.

Problem is how to spread cool air throughout the whole UN building.

By the time the air reaches the farthest corners of the skyscraper, it would lose its chill.

So Carrier decides to split the process in two. The air conditioning in the UN building doesn't cool the air, only dry it. Then it shoots the air through thin ducts to 4,000 cooling consoles mounted directly in each office.

Once you have air conditioning, you no longer need it to be near windows, so suddenly you could build skyscrapers with enormous floor plates and people would be working on an interior far away from a window.

And so air conditioning allowed for these buildings that are really, really massive. So all of these things together made the building pay to its maximum.

Air conditioning allows skyscrapers like the Burj Khalifa to rise up in even the hottest climates, and there is hardly a place on Earth where air conditioning matters more than Dubai.

Temperatures easily reach 40 degrees Celsius in the shade. The humidity is 90%, a truly extreme environment for a skyscraper.

The key to shielding the Burj Dubai from the brutal desert sun is built into its glass skin. The air conditioning couldn't keep up if we just used normal glass.

Well, this is an actual piece of the glass that we're using on the building. We have an outside face, an inside face.

So what the outside coating does is reflects the daily solar heat that comes direct from the sun, would pass into an apartment or office.

The outside pane is coated with a thin layer of metal. Like sunscreen, the metal coating deflects ultraviolet radiation that would otherwise heat up the building.

But the sunscreen is useless against the infrared that radiates from the hot desert sand. So the inner pane is coated with a thin layer of silver that keeps the heat rays out.

Burj Khalifa – Skyscraper Supremacy – Big Bigger Biggest (Part 1)

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