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 from big to bigger into the world's biggest. [Music] [Music] 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. [Music] The centerpiece in the grand plan is the Burj Dubai, the tallest skyscraper in the world. It is the ultimate leap in a series of

historic engineering breakthroughs [Music] foreign [Music] 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. Oh, 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 reach the sixth floor, seventh floor, you're incredibly winded. Ah, that's it for me [Music]. There's an obvious solution to the problem: the elevator [Music].

but early elevators have one deadly fault: nothing stops them from falling if the rope breaks. [Music] 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. [Music] 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. [Music] 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. [Music] 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. Thank you 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. [Music] 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. [Music] 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 controlled stop, is still a mechanical device. Foreign all safe gentlemen all safe. [Music] 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 flat iron building in New York. The skyscraper must be reinvented. [Music] This is the Monadnock building in Chicago, a living fossil in the skyscraper world. When it opens in 1893, it's the world's largest office block, but its 16-story stretched stone to the limit. The walls at the bottom must be a warping 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. [Music] 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 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. Stone is out of the question, but if you look at the Fuller flat iron 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 flat iron 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 flat iron 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. [Music] The skeleton of the Burj Dubai combines the best of steel and stone. [Music] It uses over 30,000 tons of steel, but in a very clever way. Steel is embedded in artificial stone concrete. [Music] This reinforced concrete backbone will be cleared 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. [Music] 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 into 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 how an inherent design flaw like at Lake or something until after it was occupied and the first storm came. It's unthinkable. 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 freshens? [Music] The buffeting and the movement of the water across the surface is finding weaknesses and if there's any flaws and 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 bourge 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 catapult 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. 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 wanted to cover the building with glass to make the interior as bright as possible. What they didn't want was 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, oven 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. [Music] 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. [Music] The 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 dries 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 Dubai 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 percent, 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 pain is coated with a thin layer of silver that keeps the heat rays out. Over 30,000 glass panels, enough to cover 17 football fields, will protect the Burj Dubai from the scorching heat. [Music] Air conditioning allows ever more people to work more comfortably inside skyscrapers, and taller skyscrapers housing more workers offer greater profits. The only problem is that bigger skyscrapers take much longer to build. Um, to reach the dizzying 417 meters of the World Trade Center, engineers have to invent a new, much faster way of building skyscrapers. [Music] Long before the Twin Towers in New York become the tallest buildings in the world, their developers face a mammoth problem. [Music] The minute they start construction, the clock starts ticking. Every day their building is unfinished costs them dearly, so they have to work out how to reduce the construction time to the absolute minimum. The solution they come up with is to

pre-fabricate sections of the towers and assemble them like a giant jigsaw puzzle. [Music] They build the sections off-site and ship them to the tower's construction site precisely when they are needed. The only problem is how to lift super heavy 50-ton sections into place quickly enough. The traditional tool to build skyscrapers like the Empire State Building is the derrick crane, but to get derricks from one floor to the next, they have to be disassembled, carried up, and reassembled, a process that can take two days. Such a crane is not going to be fast enough for the World Trade Center. These buildings were higher than anything had been constructed in the past, so naturally, we cast our eyes about the world to see what was there and what might be better suited to the project. The team found a revolutionary crane in Australia. It can lift 50 tons, and four of them can reach into every corner of a twin tower. And once they have assembled three floors, an amazing thing happens.

the bottom of the crane releases, glides up three stories, and locks back into place. And then the whole crane jumps itself up to the next level. That's why it's called the kangaroo crane. [Music] They were fast, they had some defects, they spread a lot of oil around, so it was a constant cleanup operation after them, and so forth. But they were fast and quite reliable. Foreign with the help of the pre-fabricated sections and the jumping kangaroo cranes, the Twin Towers take shape rapidly. The builders managed to finish up to two floors every week. [Music] In 1970, World Trade Tower 1 becomes the tallest building in the world, and while even more floors appear at the top, tenants move in at the bottom. [Music] Time is money. [Music] On the Burj Dubai, the kangaroo crane is still the crane of choice. [Music] Here, the builders have taken pre-fabrication to a new level because we couldn't build it fast enough, because time is very, very expensive, but

commodity because you're not making your revenue to pay for the building until the building's occupied. But nowadays, concrete building is like a factory. They're like vertical factories. They kind of jump themselves up the building as you put up the concrete, so you can go quite quickly. Is that they get a floor, virtually every three days. There's a new floor, a new floor, new floor. Key to speed is a new technology called jump forming. The process starts at the bottom of the building. [Music] Steel workers assemble steel cages that will become the backbone for the floors and walls of the boards to buy the kangaroo cranes. Hoist the steel cages up and slot them into special molds called jump forms. In goes the concrete, and 12 hours later, when the concrete hardens, the form gets ready for the jump. Hydraulic pistons push the form up, leaving the concrete block behind. It takes only two hours for the form to move up to the next level, where the process starts all over again. This way, the bourge Dubai is cast in

place layer by layer like a giant wedding cake, but delivering concrete to the top of the tower gets more difficult with every floor. It's five o'clock, and the man on the day shift goes home. [Music] [Applause] But on the top of the Burj Dubai, the casting crew are waiting for the concrete to arrive. What we're standing on right now will be the 155th floor. Uh, so gonna pour some walls tonight. Below, workers prepare the pumps. They can really only pour concrete at night because in the searing daytime temperatures, the concrete would overheat. They need 630 horsepower pumps to cope with the 25 tons of concrete contained in each pipe, and they're about to pump this concrete higher than anyone has ever done before. An amazing challenge for the pumping system. [Music] We're pumping 570 meters at the moment, which is a world record for a building site. It's a very aggressive environment within the pipe with the high pressures, the aggregates rubbing against the steel. You've got to watch out because you can

wear through the steel and the pipes first. It takes 40 minutes for the concrete to travel up the pipes from the bottom to the 155th floor. It's a combined effort of raw machine power and subtle chemistry. If the concrete is too thin and sets slowly, it causes delays. If it's too thick, it may set too soon and block the pipes. That night, it takes until 4 AM before the job is finished. Now the concrete and steel skeleton of the Burj Dubai is nearly complete on a mammoth project that will cost about one billion dollars to build. Every day is precious, but the system has worked to perfection. The tower is nearly 600 meters tall, and a new floor goes on every three days. [Music] Patient technology allows giant skyscrapers to grow even faster, which makes them even more profitable and desirable. But as skyscrapers soar even higher into the clouds, they become exposed to a new enemy, one that exploits every weakness: the wind. To build the 442-meter Sears Tower in Chicago, the proverbial Windy City.

Engineers must turn the skyscraper inside out. [Music] 70. The architects building the new headquarters for Sears and Roebuck in Chicago face a problem. Their skyscraper, the Sears Tower, will be over a hundred floors tall, a height that exposes it to huge wind forces. Building this skyscraper using a traditional steel skeleton would cause massive problems. The taller a steel skeleton gets, the more susceptible it is to bending in high winds. Gusts off Lake Michigan can buffet the skyscraper at up to 80 kilometers an hour. This causes the upper floors to sway, affecting the workers inside. The motion of tall buildings is more like the motion of a ship, creating a kind of sea sickness. There's that same sense in a very tall building, so it's necessary to reduce the swaying component down so the people are not sick. The architects of the Sears Tower invent a technology that can beat the wind. They shift the steel framework from the inside of a building to the outside. This so-called exoskeleton makes it very

hard for wind to bend the building in the Sears Tower. Nine such tubes locked together to make the building rock solid. The exoskeleton is the best way of resisting wind ever invented. Even at wind speeds of over 90 kilometers per hour, the top floor of the Sears Tower only moves 15 centimeters. The Burj Dubai is expected to be nearly twice as tall as the Sears Tower. At this extreme height, fighting the wind with a rigid exoskeleton is not good enough to stop the high-caliber residents from getting seasick. The architects turned to highly advanced aerodynamics. The most important thing in a tall building is the way it interacts with the wind. And so, what we did is we essentially, as we designed this building, we kept testing in the wind tunnel. And when we use the wind tunnel as part of our design process at high speeds, wind can be extremely dangerous for a skyscraper. Air rushes around the building and forms mini tornadoes called vortices. These areas of low pressure suck the building sideways and the toll of the

building, the more dangerous the vortices become, and these large forces are actually perpendicular to the direction of the wind. If a tall building were ever to fall down the wind, it's most likely it'd fall down sideways to the wind, not in the direction of the wind. So, on the Burj Dubai, rather than fight the wind, Bill and the design team decided to deceive it. They don't make the tower flat and rectangular; they give the Burj Dubai a more unpredictable shape. Each section of the tower is designed to deflect the wind in a different way. This disrupts the power of the vortices and breaks the hold of the wind on the building. As the wind blows across it, it never gets organized because every single portion of the building will shed vortices at a different rate than the rest of the building. And we call this confusing the wind. So, we actually, when we designed the building, we're actually designing the wind and the way the wind behaves around the building, and it makes a tremendous difference. We would

never have been able to go this tall if we had not done that with Mobility, gravity, heat, and wind conquered the skyscraper. Faces its next big challenge in Asia, where booming economies want to show off their wealth. Super tall skyscrapers become the object of Desire, but Asia is Rife with the Nemesis of tall buildings, earthquakes. To build the 509-meter Taipei 101 skyscrapers, take another leap forwards. [Music] In 1999, The Architects of the world's tallest skyscraper, the Taipei 101 in Taiwan, face a problem. Taipei sits near the Pacific Ring of Fire, the most seismically active area on Earth. An earthquake hits the city roughly twice a year. The it's not a question of if but when the earth will shake the Taipei 101. Quakes are actually really strong compared to wind, for example. Wind loading very rarely will break a large building, but for an earthquake, it's actually quite easy to do. With that, Adam crew will test a model building on

an earthquake simulator to make it realistic. This model is built with spaghetti. Spaghetti and steel are actually quite similar in the way they behave. You can actually see that it buckles quite nicely. It's a relatively low load, and steel beams behave in a very, very similar way. So, it models steel really quite well. With the top floor glued in place, the model is ready to face the tremors. Here comes the slowest, the first earthquake. You can see the building really isn't moving very much at all. Looks pretty solid, so not really being bothered by this earthquake. It's a bit of a faster earthquake now. Again, a little bit of movement, but the building looks really nice and strong. Even faster, and oh, and it's gonna go. It looks like [Applause]. If that had been a real building, the forward would have fallen down, and all the people would have been killed. So, although it looks relatively intact, this is really a catastrophic failure for a building. Adam crude tests a second model that has elastic bands added to the spaghetti. So, here comes the earthquake that

smashed the other building. See how well this one does. You can see it's moving a lot, but it's actually performing really well. The top of the building is actually hardly moving at all. It's literally staying there stationary, and the ground is moving really quite violently underneath it. So, slightly bizarrely, by making the building more flexible, you've made the building stronger to survive in fast and violent quakes. The Taipei 101 needs a dash of elasticity, so the designers make their building rigid where it has to be, but flexible where it can afford to be. At the heart of the Taipei 101, they put 36 rigid steel tubes filled with concrete that give the building strength. While the columns stand firm during a quake, the rest of the structure is elastic. It can flex and roll with the punches. Mother Nature tests this design to the limit. The 31st of March 2002, an earthquake hits the Taipei 101. The quake has shattered smaller buildings, but the Taipei 101 is still

standing an extra layer of protection had saved the day. The engineers had shielded the building's vulnerable points by making the steel beams next to them thinner. These beams are called the dog bones. They had twisted and stretched like crumple zones in a car, absorbing the energy of the quake and preventing the tar from collapsing. [Music] The engineers of the Taipei 101 claim that during a quake, their building is the safest place in town. The bullish Dubai can withstand earthquakes of up to six on the Richter Scale because it has a massive reinforced concrete skeleton. But here, the engineers face a different problem. Making a super tall building stand up in the desert sand requires special measures. At the Burj Dubai, they have rock relatively shallow, but it's very, very poor rock. It's very weak, it's very fractured, and it anatomic can't carry a lot of weight. So they went 50 meters down deep into the rock in order to get enough of Iraq to support that structure. 50 meters at the bridge was really at

the limit of what rotary drilling equipment probably could do in that area. Drilling into the rock in Dubai may be hard, but it's when you pull your drill out that the real trouble starts. The rock under the Burj Dubai is fragile and saturated with groundwater. Any big hole will cave in immediately. To stop this from happening, the engineers fill the boreholes with a viscous polymer slurry, which pushes the groundwater and rock fragments to the edge of the borehole and keeps it open. This is polymer slurry. It's really kind of just a heavier fluid. The polymer is a kind of a space-age material, and what it does is it makes very long molecules or chains so that we add it to the water. It kind of makes very long tendrils that come out that viscosity and helps to keep the excavation from caving in. The secret name for the contractors on site is basically to call it snot. Syrupy polymer is denser than water but lighter than concrete. The concrete displaces the slurry and eventually hardens to form a foundation.

pile [Music] 200 of these piles work together to stop half a million tons of real estate from sinking into the ground. So far, it has gone down around 30 millimeters, which is slightly more than an inch. It's about the thickness of my thumb, which is a very small number for a building of this size. Foreign [Music] thank you [Music]

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

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