To gain the other side, to cross the bay, a curiosity, then an obligation which pushed the Man, from the first times of its history, to develop techniques of construction to overcome these obstacles. From the first bridges in liana, through the Roman aqueducts to the viaduct of Millau which spans the valley of the Tarn to 270 m in height, the genius of the man was expressed in the civil engineering…These technical feats, traits of union between men, are, in the broad sense, true works of art. Thus man has developed, thanks to science and its applications, a way to get closer to other men and to become master of time, and space.
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TVTranscript
00:00Reaching the world on the other side, crossing the bay, first a curiosity, then a necessity,
00:13one which has urged man from the dawn of his history to develop construction methods that
00:18enable him to cross barriers. But bridges are more than just technological feats,
00:25they are links between men.
00:30Lea Bello is a geophysicist. She'll be following in the footsteps of exceptional builders,
00:41revealing the secrets behind the construction of iconic works, and discovering the challenges
00:49faced by engineers who build even higher and even further.
01:00No engineer in his right mind would have chosen this place to build a bridge. Unfortunately,
01:08that was where a bridge was needed.
01:11A scientific investigation to discover how men design and construct civil structures.
01:21True expressions of human genius to bridge the gap.
01:25True expressions of human genius to bridge the gap.
01:37True expressions of human genius to bridge the gap.
01:45Lea Bello first heads to northeast India and the state of Meghalaya to discover a hidden
02:06treasure.
02:08Located on the border with Bangladesh, a third of the state is covered by dense, damp forest.
02:15Numerous streams wind through the valley, representing obstacles for the movements of the villages.
02:22For almost 500 years, they have intelligently tamed nature by building bridges, using the
02:28roots of living trees.
02:32Be careful, it's very slippery.
02:37Slowly, here is the bridge for you, the living road bridge.
02:45See the roots.
02:52It's like something out of a fairy tale.
02:58Is the bridge still in use?
03:00Every day.
03:01Every day, we have people living in the village on the top.
03:04They come through this to go to their garden.
03:07Monsoon time, it's so much water.
03:09Without this bridge, they cannot cross this.
03:11This kind of activity had been going on for many centuries in this area.
03:16So it's been a common thing here.
03:18This is ficus elastica.
03:19It has got long stem roots.
03:21It can sit on rocks and chen roots into the streambed.
03:26So that's how they started using this.
03:27It grows very well alongside streams and rivers.
03:32And see the size of the roots.
03:35This bridge is so strong.
03:36It can carry 100 people.
03:39Abandoned in the 1980s in favor of new concrete bridges, the living bridges have been the subject
03:45of a rehabilitation program launched 15 years ago.
03:49Today, local inhabitants protect these wonders of nature.
03:52In all, the valley has about two dozen of these bridges, some of which span 20 meters.
03:58Where we are going to show you the last, but not the least, and the best in this place.
04:03There are two bridges.
04:06We have the double-decker.
04:08Very special bridge.
04:11The only one of its kind in the world.
04:14It's the unique double-decker root bridge.
04:17Unique in the world, the living root bridges of Meghalaya are also the only bridges to actually get stronger with age.
04:25This exceptional example of bioengineering illustrates just how man can tame his environment
04:31to build foot bridges to take him over natural obstacles.
04:35The first bridges in history were all built using plants, or plant-based materials.
04:44Vines, rope, wooden planks, and so on.
04:48Primitive bridges, which are still constructed and maintained in some parts of the world, like in the foothills of the Himalayas.
04:57In less forested areas, man turned to a more resistant material.
05:01Stone.
05:03Some of these prehistoric bridges still stand today.
05:10During the final millennia before our era, Stone dominated the history of bridge building, until the Romans perfected the art.
05:18For almost five centuries, the Roman Empire reigned over Europe and the Mediterranean.
05:29To expand their territory, the Romans developed an important network of roads and bridges.
05:34This construction-minded people built numerous large-scale structures in stone, some of which are still standing after 2,000 years.
05:43Like the Pont du Gard in the south of France, which was constructed in the middle of the first century of our era.
05:49It's dimensions are impressive. 47.6 meters high, with a span of 275 meters.
06:00This iconic vestige is the highest elevated Roman aqueduct bridge in the world.
06:06From the bottom up, its three tiers have six, eleven, and thirty-five arches respectively.
06:10Vaulting has been used since the Mesopotamian period, but not all the time.
06:16The solution discovered by the Romans was to build semicircular archers with centring, with the lateral thrust exerted on piles with very strong foundations.
06:24This produced much wider arch spans, from a few meters to 35 meters across.
06:31Once the piles were sunk into the riverbed, the next task was to construct the archways.
06:37The semicircular vaulting forms a structure which can span an empty space with successive arches.
06:43To build the arches, a solid support was needed, known as a centring.
06:47This constituted two wooden semicircles with the same form as the intended arch.
06:52And served as the framework.
06:56The blocks of stone were then laid on top of the wooden centring, until the last one, the keystone.
07:05On the first tier of the bridge, the arches were thus formed with three parallel sections of stones.
07:11This form allowed the Romans to build arches with unprecedented spans.
07:17But it did have its limits.
07:20If an arch were to span more than 40 meters, the quantity of stone would be too heavy, and the vaulting would collapse under its own weight.
07:28It's often said that the Romans were the greatest builders in antiquity.
07:35But what do we know about the exact construction techniques and methods they used?
07:40We know a huge number of things, but not everything.
07:43Firstly, their construction techniques were absolutely remarkable.
07:47Their level of engineering clearly surpassed that of the ancient Greeks, who were also great engineers.
07:52And Vitruvius, the Roman architect and engineer, left us the only known book on the subject, which we can now consult for all our studies of the archaeology of antiquity.
08:03Vitruvius was the author of the only surviving treaty on the architecture of antiquity.
08:10It's an exposé of the art of Roman construction, and it lists the tools and techniques employed by these master builders.
08:19From a theoretical point of view, we learn of their acute sense of proportion.
08:24The lines of their buildings form harmonious dimensions, and employ incommensurable numbers such as pi, or the square roots of three and five.
08:33The Romans set out to construct for eternity.
08:44Their use of infinite numbers actually enabled them to obtain the absolute.
08:48And also, thanks to this geometrical system, stonemasons also knew the methods perfectly.
08:53And so they could reproduce on the spot, on a much larger scale of course, the plans which had been drawn by the architect.
08:59While the Pont du Gard remains a model of aestheticism and architectural perfection, it was actually constructed for a very precise purpose.
09:13To bring fresh water to Nîmes, one of the largest cities in Gaul, with 20,000 inhabitants.
09:23The spring chosen was the Fontaine d'Eure, some 50 kilometers away from Nîmes.
09:27The distance wasn't a problem for the architects, but something else was.
09:34They had hoped to find a spring much higher up than the arrival point.
09:41But unfortunately, the Fontaine d'Eure was only 17 meters higher.
09:47That meant the builders had to construct an aqueduct with an extremely gentle slope, one of the gentlest in antiquity.
09:54How gentle was it?
09:5724 centimeters per kilometer.
10:01A gradient equivalent to only one millimeter every four meters.
10:05And without expert calculations, it was impossible to ensure a regular slope along the full 50 kilometers of the aqueduct, especially across the Pont du Gard.
10:15That means that you have a channel with a slope like this, fairly steep, followed by a very gentle slope, and then another steepish one.
10:25So in the central part, the bridge, water flowed much more slowly.
10:29So the result is the water rose in the channel, and once the aqueduct was in service, they realized that it overflowed from the Pont du Gard.
10:36So the original wall only came up to here, and to stop the water overflowing, they had to build up to here?
10:43Exactly.
10:44This masterwork of antiquity supplied Neme with water for almost 500 years, until the fall of the Roman Empire.
10:55The construction of immense architectural and engineering works disappeared with the Dark Ages, and was only resumed 500 years later, in around the year 1000, with the expansion of Christendom and the power of the Church.
11:07The builders of the Middle Ages re-adopted the techniques and methods of Roman architects.
11:21Over the following centuries, some bridges were remarkable, because houses and shops were constructed on them.
11:28Most of these have disappeared, such as the old London Bridge, and Notre Dame Bridge in Paris.
11:34But others have valiantly survived, like the Rialto Bridge in Venice, and the Ponte Vecchio in Florence.
11:42But there was no true architectural evolution until the Renaissance.
11:47Between the Roman Empire and the Middle Ages, there was pretty much no progress from a technical viewpoint.
11:54The real break came later, in the late 17th century, early 18th century, with a noticeable lightening of the general line of bridges.
12:04Gradually, semi-circular arches with centering were replaced by elliptic arches, which offered a wider arch span.
12:14Consequently, bridges became lighter and slenderer.
12:17And this meant they could cross greater distances.
12:27But it wasn't until the middle of the 18th century that the first big technological break came, with Jean-Rodolph Perronnet.
12:33Considered to be the father of modern engineering, he was also the first to understand the true mechanics of a stone arched bridge.
12:42He established that each arch was not freestanding from the others, and that the thrust was shared between the spans.
12:54This crucial observation meant that the thickness of a bridge's piles could be considerably reduced.
12:59Perronnet halved the thickness of the piles.
13:06He developed an understanding, somewhat systematic one could say today, of how bridges functioned.
13:13So he built bridges in a different way to traditional ones.
13:18With his bridges, the thrust of each span kept the others in equilibrium.
13:24Unlike the Pont d'Avignon, where if one arch collapsed, others might yield.
13:28The arches of the modern bridge were much more interlinked, and the thrust went from arch to arch, right to the abutments.
13:38Stone thus dominated the history of bridges until the Industrial Revolution.
13:43In the late 18th century, early 19th century, the mastery of iron allowed engineers to design structures with new profiles.
14:03Iron was the great revolution for bridges.
14:07It was about 60 times more resistant to pressure and thrust than stone.
14:11And that would lead to considerably lighter structures.
14:15Iron resisted tensile strength as well as pressure.
14:19That meant that architects could finally drop the arch, which had been the dominant form of bridges since Roman times.
14:28Iron enabled builders to construct bridges with triangular crossbars.
14:33Both lighter and more resistant, bridges could span even greater distances.
14:42The rapid development of the railways demanded new technological solutions to cross rivers and valleys.
14:50Engineers stopped at nothing, like spanning the deepest gorges where no one had ever dreamed of taking on nature, and bridging the gap.
15:04The Garabay Viaduct is a striking example of this daring.
15:11It was designed by Gustav Eiffel, a visionary engineer and determined architect, whose solid yet elegant bridges reached heights that gave his contemporaries vertigo.
15:22Located in the heart of the Massive Centrale, the Garabay Viaduct crosses extremely undulating terrain.
15:32565 metres long and 120 metres high, the rail bridge rests on seven piles and a single main arch, with a span of 165 metres.
15:50What was there here before the construction of the bridge?
15:52Nothing. At Garabay, absolutely nothing. They had to lay new roads just to get to the site.
16:01Then, they had to construct accommodation for the men who would work on the viaduct.
16:07Why construct a bridge where nothing existed?
16:10So that the train, with its passengers and goods, could reach the region.
16:15It's just to see.
16:17As rail was developing everywhere in France, there was still no line through the Cantal department, linking Paris directly with Bézier, without skirting around the Massive Centrale.
16:30Here it is.
16:32Wow.
16:36The gigantic worksite began in 1880.
16:39The viaduct was erected in just four years, an incredible technological feat for the time.
16:56Keep going. Almost there.
16:57The Garabay viaduct was the test bed for revolutionary technology, and it was while constructing this bridge that Gustave Eiffel patented his famous lattice girders, used several years later for the Eiffel Tower.
17:20The structure is mesmerizing, totally fascinating, and in the signature Eiffel style, with the open lace girders, which allows the wind to pass through.
17:33That's right. It's a very airy structure.
17:37How was it constructed? Was the whole thing just assembled here?
17:41Half of it was pre-assembled in the workshops in the Valois Perret near Paris. The other half was hot riveted together here in Garabay.
17:51The wrought iron girders were assembled with rivets, these small shafted iron fasteners inserted between each piece of the structure.
18:00Once heated to red or white hot, and the tail of the rivet has been hammered flat, they hold the pieces together when they cool.
18:07Once the bridge was finished, it must have been a huge event for the region.
18:12Yes, and not only for the region, but the whole civil engineering world.
18:17The bridge was marveled at, due to its height, as far as the United States.
18:22It's one of the two most talked about works by Eiffel among the hundred he built around the world.
18:27The Garabay Viaduct and the Eiffel Tower, erected four years later, are testaments to Gustav Eiffel's genius and perfect mastery of iron.
18:46Iron dominated the history of bridges in the late 19th century.
18:51Constructions multiplied throughout Europe and the United States.
19:03But few engineers understood how iron, and notably cast iron, would react over time with the constant crossings of trains.
19:10Often hastily constructed, bridges became the stage of some terrifying disasters.
19:18In the United States, almost 200 of them collapsed in the 1880s.
19:24These repeats marked the end of the iron bridge.
19:35Engineers turned to a new, much more resistant material.
19:39Steel, an alloy of iron and carbon, the development of which took metal work from the domain of craft work into that of science.
19:47One, high quality steel has far superior mechanical qualities compared to iron, so you can go much further with it.
19:57Two, it had a big impact from the early 20th century on, because, unlike iron, it could be welded, and that would totally transform assembly technology.
20:07Today, no one would even imagine building a large work of engineering without steel.
20:11Steel opened the door to rapid technological progress.
20:20Across the globe, sleek-looking bridges sprung up across rivers,
20:25breaking records with spans of several hundred metres, like the Forth Bridge in Firth, Scotland.
20:31But back to the early 19th century, another method of construction was born in the United States.
20:56The suspension bridge.
21:00Bridges where the road deck is hung below wire suspension cables, firmly anchored in abutments on the riverbanks.
21:11The suspension bridge is a very simple idea, and it's not that complex to construct.
21:18The main thing back then was to make sure the steel used in wire cables was of good quality, so that they wouldn't snap.
21:26There was a lot of debate because, for a long time, bridges were suspended by chains, then by cables, then by modern groups of cables.
21:34With cables made of steel, suspension bridges became all the rage.
21:40But it was the daring of a German-born engineer which would give the United States one of the wonders of the modern world.
21:48The Brooklyn Bridge in New York.
21:50To better understand how this bridge changed the history of engineering and that of New York,
21:59Lea Bello joins Dave Frieda on the banks of the East River.
22:03This photographer, a specialist in bridges, is a fountain of knowledge when it comes to the Brooklyn Bridge.
22:17This legendary bridge, 1,825 metres across, beat all span and height records.
22:35Construction started in 1870, giving rise to an era of ambition and sacrifice of an entire family.
22:41The Roeblings.
22:50John Roebling, who designed the bridge, unfortunately he didn't have a chance to see his bridge completed.
22:56He was surveying the footings for the bridge on the south side of the Brooklyn Tower.
23:05A ferry had come in, he didn't see it, and it crushed his foot.
23:09And the only treatment he wanted was pouring water on it.
23:12Unfortunately, he died of tetanus.
23:14So his son, Washington Roebling, then took over as chief engineer.
23:18So Washington was the one who actually built the bridge.
23:20He went down into the caissons to help the men dig out the muck and the rocks below.
23:28He wanted to be part of the team.
23:31But they didn't know again about caisson disease, about the change in air pressure.
23:35He wound up being laid up in his bed, in his bedroom.
23:39So his wife, Emily Roebling, then transferred all the information from him, Washington, to all the workers.
23:44So Emily Roebling was very instrumental in helping building the great Brooklyn Bridge.
23:51She was one of the first woman civil engineers that really helped.
23:55What she did was absolutely incredible.
23:57I think without Emily Roebling, you wouldn't have the Brooklyn Bridge today.
24:05The construction of what was then the world's biggest suspension bridge was dotted with numerous problems and disasters.
24:12Starting with the most ambitious and dangerous stage in the project,
24:17the sinking of the immense foundations in the bed of the East River.
24:26The construction of the foundations employed an innovative process.
24:30Washington Roebling had two giant wooden caissons made, measuring 50 metres long by 30 metres wide.
24:37The imposing blocks of granite for the towers were laid on top, which gradually sank the caissons to the riverbed.
24:46Once there, at a depth of 30 metres, compressed air was injected into the giant boxes so they could resist water pressure.
24:57In this damp, cramped, pressurised space, labourers dug for several months in order to anchor the piles in the bedrock.
25:09The rubble and mud rose to the surface via a central conduit.
25:14And within only four years, the two towers had begun to rise from the East River.
25:21At the time, little was known of the effects of pressure on the human body.
25:27Contractors and workmen began to suffer from strange illnesses.
25:31The caissons on the Manhattan side were at 30 metres deep, which means the pressure inside would have been three times more than surface pressure.
25:42That must be what made it so dangerous for the men working inside when they returned to the surface.
25:46Yes. I used to scuba dive, so I know the dangers of decompressing.
25:53If you come out to ambient pressure too fast, it's like opening a soda bottle.
25:58Open the top too quick, the gases come out too fast.
26:02That's the same thing with the nitrogen in your blood.
26:05It would come out, it settles into the joints, it's extremely painful.
26:08So they now know you have to come out into ambient pressure very slowly.
26:13They didn't know that back then, so they called it caisson's disease because almost everyone that went into the caisson came out in extreme pain.
26:23A lot of men died.
26:25Despite the numerous challenges, the 90-metre tall towers were completed in 1875, and the installation of the cables could begin.
26:36This is the four main cables. These main cables is what holds up the road deck.
26:40Each cable contains wires like this. 5,434 wires make a 15 ¾ inch cable.
26:50Each cable can withstand the pull, tension of 25 million pounds.
26:55They were anchored in anchorages on both sides of the bridge.
26:57The main cables are original. Some of the engineers I know worked on the bridge, and the cables that are made of wire like this are in great condition.
27:13They're galvanized. This is the first suspension bridge in the world to use galvanized steel wires.
27:18It's steel coated with zinc. Zinc oxidizes, but it doesn't rust, and it protects the steel underneath it.
27:25So this can last two, three hundred years easily.
27:27To prove the solidity of the cables, master mechanic E.F. Farrington crossed the East River, suspended from them.
27:40In all, 23,000 kilometres of cables were installed.
27:44After 13 years of work, the bridge was finally completed. Its inauguration on May 21st, 1883, was a national event.
27:57All of New York was invited. The president was here. The mayor was here. It was called Decoration Day.
28:06The entire city basically shut down to celebrate the opening of the Brooklyn Bridge.
28:11A week later, there was what's called the bridge stampede.
28:15Someone had tripped on Decoration Day a week later, and people thought the bridge was collapsing, and a lot of people were trampled to death, unfortunately.
28:22So to compensate for that, Washington Roebling had a whole herd of elephants to walk across the bridge.
28:29And that proved to the public that the bridge was very safe.
28:34I believe this bridge can't last for centuries. It is a marvel of engineering.
28:39Hopefully many future New Yorkers and other people around the world will be able to see this great structure.
28:43The Roebling's Brooklyn Bridge is now known the world over, and is one of New York's most iconic landmarks.
28:57Over 130 years later, it's still standing. A genuine work of prowess, given the know-how of the time.
29:04It inspired other famous large bridges, like the Washington Bridge on the other side of Manhattan.
29:17And the Golden Gate in San Francisco.
29:22But other bridges have proved less long-lasting. The first Tacoma Narrows Bridge in the state of Washington would collapse under the effects of a suspension bridge's main enemy, the wind.
29:39Last July, the nation hailed the opening of the new $6.5 million Tacoma Narrows Bridge over Puget Sound.
29:47This is the opening of the Tacoma Narrows Bridge, right?
29:51Yes. It was inaugurated on July 7, 1940, and the bridge started oscillating up and down from the outset.
30:01During the summer of 1940, people visited the bridge just to see it swaying. It became a tourist attraction.
30:08And it became famous.
30:10Yes, from the very beginning.
30:11Except that in November, there was the first storm of the fall.
30:19It wasn't a big storm, but there were winds of 70 kilometers an hour through the strait.
30:24And instead of oscillating up and down, the deck started to twist.
30:31From one side to the other, there was an amplitude of almost 9 meters.
30:35And after an hour, at about 11 o'clock in the morning, the whole central section gave way and collapsed into the Tacoma Narrows.
30:48Oh, yes. There it goes.
30:51Which leaves us with a marvelous example of how not to build a suspension bridge.
31:04One of America's finest structures...
31:06Fortunately, the collapse of the bridge claimed no victims, except for a terrified dog locked in the car in the middle of the bridge.
31:14Not a person was lost, but it's a real tragedy.
31:17When the wind blew on the Tacoma Narrows Bridge, air pressure was exerted on the edges of the deck, transferring its energy into the structure itself.
31:34And causing the roadway to bend and sway.
31:36After the collapse of the bridge, architects and engineers began to study much more deeply the impact of the wind on bridges.
31:53But it wasn't until the 1970s that aerodynamics became a science in its own right.
31:58From then on, the decks of bridges were streamlined to facilitate the flow of air around the structure, so as to prevent any risk of swaying.
32:10With the invention and mastery of new materials, during the 20th century, man would be able to build longer, higher bridges with even more impressive dimensions.
32:23It was the age of concrete, the king of bridge building, and much cheaper than steel.
32:37And it would benefit from a revolutionary process developed by French engineer Eugène Fressinet, which was perfect for civil engineering works.
32:46Pre-stressed concrete.
32:47Pre-stressed is concrete that has been compressed so that the traction exerted on it is more than compensated by the stress exerted on it.
33:00For example, if you make a beam out of sugar cubes, it won't resist traction at all.
33:06But if you compress the cubes, you can then place a small object on them, say an eraser, and the sugar beam will hold firm.
33:13Because the disintegrating effect produced by the eraser's weight is nullified by the fact that the cubes are more tightly packed together.
33:24This new material has been used on most of the bridges which stand today.
33:29And it will be used in hybrid bridges, such as cable-stayed bridges, constructed with a mixture of concrete and steel.
33:35A cable-stayed bridge doesn't need the expensive anchoring of the suspension bridge, because the deck is no longer suspended from a gigantic main cable, but supported by series of individual cables running directly from the pylons.
33:52This new model spread across the globe in the second half of the 20th century, breaking all kinds of records, like in 1995 with the Pont de Normandie and its span of 856 metres.
34:08Nothing seemed able to halt the ambitions of architects and engineers.
34:16Not even the wrath of nature which has managed to destroy a number of their bridges, like during the earthquake in Kobe, Japan in 1995.
34:26Across the Gulf of Corinth stretches the Rio-Anterio Bridge.
34:37It links the Peloponnese to mainland Greece, at a point where two and a half kilometres separate the two shores.
34:44The region sits between two tectonic plates, making it one of the most seismic in Europe.
34:55No engineer in his right mind would have chosen this place to build a bridge. Unfortunately, that was where a bridge was needed.
35:04Project director Jean-Paul Tessandier worked for over five years with overseeing engineer Gilles de Maublanc.
35:15Together, they came up with unprecedented solutions.
35:21The first difficulty was the depth of the water, 65 metres.
35:25That's no longer the field of bridge building, but of offshore engineering.
35:29Secondly, the seabed was of a very poor quality.
35:34And thirdly, there are faults that are constantly active, meaning the distance changes between the two coastlines.
35:42And during a strong earthquake, there could be a sudden change of several metres.
35:51When we discovered the scale of the work, we were sorely tempted to close the file and refuse it.
35:59At the same time, we liked the idea of facing a massive challenge.
36:04And we thought, there must be a solution.
36:09The bridge has to be capable of withstanding earthquakes of up to seven on the Richter scale.
36:17So the main challenge was to lay sufficiently solid foundations to ward off the wrath of the earth.
36:22But preliminary studies showed the seabed to be particularly unstable.
36:32With the poor quality of the seabed, our first idea was the classic one, to dig down to find better quality ground.
36:41But after detailed analysis, we soon found out that the bedrock was at a depth of about a thousand metres.
36:51So that was totally unfeasible and unrealistic.
36:55Then, after doing a lot of research, we came up with a totally innovative concept.
36:59Due to the extreme depth of the bedrock, the engineers soon abandoned the idea of laying foundations under the seabed.
37:08Instead, they decided to consolidate it using a brand new solution.
37:12Each of the four huge pylons rest on groups of 200 hollow steel pipes driven into the bed.
37:18The pipes measure 25 to 30 metres long, with a diameter of 2 metres.
37:25These were then covered with a bed of gravel, 3 metres thick, on which the foundations, called pier footings, simply rest.
37:36The dimensions of the footings are gigantic.
37:39Each is divided into 32 compartments and have a diameter of 90 metres.
37:48They remain the biggest pier footings ever constructed.
37:54The Rio Anterio Bridge has another particularity.
37:57Rather than lower and upper pylons, there are pylons of a single block of concrete.
38:06The suspended deck is continuous from one end to the other.
38:10It passes between the pylons and is suspended by only 368 stays.
38:15It's a genuine floating roadway.
38:19So in case of an earthquake, it can gently sway.
38:23And to prevent the deck from hitting the pylons, the engineers had to come up with an ingenious system to stabilise the bridge.
38:30Let's start with the big central tube.
38:35It's a rigid tube, which holds the structure transversally in high winds.
38:41But for a major earthquake, which can't be withstood by the rigid support,
38:48there's a fuse inside which breaks, allowing the small tube to enter the big one.
38:56So one, two, three, four shock absorbers come into play.
39:03It's very similar to the shock absorbers in your car.
39:06When you go into a hole, they absorb the energy.
39:08Beneath each of the pylons, the deck is maintained by this system of fuses and 10 metre long shock absorbers.
39:18And over 400 different measuring instruments monitor the bridge's movements in real time.
39:25On June the 8th, 2008, the screen suddenly went berserk, when an earthquake of 6.5 magnitude struck the south of Greece.
39:41During the 2008 quake, things went according to plan.
39:48The connections broke, the shock absorbers absorbed the shocks, and the deck was allowed to sway freely.
39:56So it was a genuine life-size test of whether our project was well-founded or not.
40:02Thanks to the shock absorbers, during an earthquake, the deck can move laterally 3.5 metres without hitting the pylons.
40:11The bridge is an extraordinary bridge, because it's a bridge implanted in an extraordinary environment.
40:26Every bridge marks a victory over the elements, earth, water and air.
40:32And a number of them are veritable feats, due to the uniqueness of the terrain they cross.
40:37In the majestic gorge valley of the River Tarn, in southern France, the Mio Viaduct has become the new world record holder of bridges, with its 2,460 metre cable-stayed deck 275 metres in the air.
40:53It was constructed to free Mio of a curse, its constant traffic jams.
41:01But to re-route the highway, the new road would have to cross one of the deepest gorges in Europe, with a width of 2.5 kilometres.
41:08Michel Vierlogeux is a graduate of France's top engineering school, the Ecole des Ponts et Chaussées.
41:22He has worked on almost 200 bridges during his career.
41:27He's known as the father of the Pont de Normandie, and participated in the design of the Vasco da Gama bridge in Lisbon, Portugal.
41:38At Mio, the complex geography of the valley was for a long time a real brain teaser for the engineer.
41:49Several routes were envisaged because we had to cross a large network of valleys.
41:55At the outset, the elevated solution, going from plateau to plateau, didn't come to mind because of the necessary height of the pylons.
42:03And then an expert road construction engineer said to us, why don't you stay up at the same level as the plateaus?
42:10And we thought we're stupid, that's what we have to do.
42:12Never had engineers built so high up.
42:18Once the route was decided, the designer then had to imagine the profile best suited to the landscape.
42:26My idea was to construct a cable stayed bridge with multiple spans.
42:31Why? Because for the bridge to be slender and transparent, cable stays would be the best.
42:36Plus, it's also the most effective structure to bear the load, allow larger spans and thus fewer pylons.
42:43With British architect Norman Foster, Michel Villager's team worked on finalizing the plans for the viaduct for almost ten years.
42:52Work finally began in 2001.
42:54A gigantic work site on which Mark Bonomo worked as the engineer who oversaw the building of the metallic roadway.
43:11You feel tiny.
43:13Yes, you do.
43:15How many meters up is it?
43:17From here to the top, 245 meters.
43:20245 meters?
43:21It's the tallest pylon in the world.
43:28With its 2,460 meter long deck, the Mio Viaduct is one of the longest cable stayed bridges in the world.
43:36It rests on seven pairs of piles and pylons, 342 meters apart.
43:42The bridge reaches a maximum height of 343 meters, making it taller than the Eiffel Tower.
43:47What's the width at the base of the pylon?
43:53The base is the size of a tennis court, and the concrete is 5 meters thick.
44:00Underneath, there are four big piles, 18 meters deep and 4 meters in diameter.
44:07And all that anchors this pylon in the rock below.
44:12During work, the seven pylons were built at the same time to gain in speed.
44:18Each was given its own crane to pour in concrete.
44:22The pylons grew four meters every three days.
44:25In December 2003, two years after the construction began, the pylons were complete.
44:32Each of these splits in two for the last 94 meters.
44:35A characteristic shape that wasn't chosen by chance.
44:38A bridge, even when constructed to take limited deformations into account, remains extremely supple.
44:47So we had to choose a shape for the piles and pylons to give them the necessary rigidity to restrict deformations,
44:54while also allowing longitudinal dilations of the deck due to variations in temperature.
45:00It's to allow for deck movements that the piles and pylons divide into two slender shafts at the top.
45:21The entire deck was constructed on the ground, in workshops, on the plateaus either side of the bridge.
45:26A hundred and fifty men, aided by robots, carried out over a thousand kilometers of welding to assemble the steel roadway.
45:37How did you manage to get the structure in place?
45:41I came up with the idea of pushing it into position.
45:45Not a classic form of pushing, because the pylons are so high.
45:51The tallest is 245 meters.
45:54Plus, they're very flexible, so they wouldn't have resisted classic pushing.
46:01So we invented a sliding system with wedge conveyors, our famous wedges.
46:13Each conveyor was made up of two wedges, which slide over each other with the use of jacks.
46:18The first lifting wedge slid under the second, supporting the roadway.
46:23This second wedge was then raised two centimeters, and as it was no longer resting on the piles, it could advance.
46:30Once in position, the first wedge slid again, the conveyor was back to its original position,
46:36and the cycle could recommence to advance the roadway 60 centimeters by 60 centimeters.
46:45Thanks to this system, the only one of its kind in the world, the north and south sections of the deck joined up in May 2004, after 15 months of sliding.
46:55To get the pylons upright, the engineers sought inspiration from ancient techniques, and developed a tailor-made lifting system.
47:09They basically copied the model invented by the Egyptians to raise their obelisks at Luxor.
47:16Constructors must know all the techniques used for at least the past 4,000 years, whether they're Egyptian, Roman, 19th century, 20th century.
47:31When you mix all that together, you can build great works of civil engineering that will be part of the long history of human construction.
47:43So it's a blend of history and technology.
47:47After only three years of work carried out by almost 600 people, the completed bridge stood majestically above the gorge of the Tarn Valley.
47:56It was opened on December the 14th, 2004, by then-president Jacques Chirac, a proud memory for Michel Velogeux.
48:06What really touched me about the occasion was when President Chirac got out of his car, looked at it and went,
48:13that was fantastic.
48:15More than ten years after its construction, the Mio Viaduct still holds the record for the tallest pylon in the world.
48:28But in the past decade, other limits have been stretched.
48:31Recently, engineers have broken new records.
48:45With its pylons spaced 1,408 meters apart, the cable-stayed span record is held by the third bridge across the Bosphorus, designed by Michel Velogeux in Istanbul.
48:56And China has recently broken the height record, with a bridge culminating at 565 meters above the Baipen River.
49:13So are there any boundaries that can't be crossed?
49:27I don't know how far we can push the limits. We could envisage wider and wider spans, but we'd need a new kind of material.
49:42Traditional materials, like concrete and steel, will eventually become too heavy for exceptionally wide spans.
49:49A suspension bridge with steel cables has its limits. The moment it can no longer bear its own weight, you have to stop.
50:05Things will continue to evolve, but in the short term, I don't foresee any major revolution.
50:12Before erecting ever bigger bridges, engineers will undoubtedly develop new materials, but they won't depart from the founding principles, which form the singularity of these works of engineering art.
50:28Beauty and efficiency. You need the two. And that goes back to the principles of Vitruvius, 2000 years ago, which are Utilitas, Fermitas, Venestas.
50:44Utilitas is usefulness. A bridge must have a purpose. Fermitas is resistance. A bridge must hold and it must be long lasting.
50:51And finally, Vinitas, which is beauty and elegance.
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