0:00:02 > 0:00:09This is the Rion-Antirion Bridge in Greece, one of the longest bridges in the world.
0:00:11 > 0:00:16It crosses some of the most active earthquake fault lines in Europe.
0:00:16 > 0:00:20It also sits in a powerful natural wind tunnel
0:00:22 > 0:00:27and there's nothing solid at the bottom of the sea to build it on.
0:00:27 > 0:00:34To make matters worse, this coast is moving away from that coast every day.
0:00:36 > 0:00:38How did they ever build it?
0:00:38 > 0:00:41They faced what would have been an impossible challenge
0:00:41 > 0:00:44if it weren't for some unusual connections.
0:00:44 > 0:00:46The hammock...
0:00:46 > 0:00:47Go on, lads, let it rip.
0:00:51 > 0:00:52..a fizzy-pop can...
0:00:54 > 0:00:55Oh, no. There's a fire!
0:00:57 > 0:01:00This is lovely.
0:01:00 > 0:01:01..a toboggan...
0:01:04 > 0:01:06..Indian incense...
0:01:06 > 0:01:12These contain an oil that really does smell lovely.
0:01:14 > 0:01:16..and a steel chimney.
0:01:36 > 0:01:43The Gulf of Corinth slices deep into mainland Greece, but at its Western end it's very narrow.
0:01:44 > 0:01:49To avoid a 280-mile detour around the mainland of Greece,
0:01:49 > 0:01:55you only need to cross this small stretch of water. Sounds simple.
0:01:55 > 0:01:58On one side of the Gulf of Corinth, Rion.
0:01:58 > 0:02:03On the other, Antirion. You can see what they did. Rion, Anti-Rion.
0:02:03 > 0:02:09100 years ago, the Greek Prime Minister dreamed of a bridge to connect the two places.
0:02:09 > 0:02:15Without some unprecedented engineering, that bridge would still be a dream.
0:02:26 > 0:02:29Nearly two miles in length,
0:02:29 > 0:02:36the Rion-Antirion Bridge is really long, but most incredibly, it's practically earthquake proof.
0:02:36 > 0:02:44Which is reassuring, as it sits in one of the most active seismic zones in all of Europe.
0:02:47 > 0:02:51It can withstand shocks measuring 7.4 on the Richter scale,
0:02:51 > 0:02:54enough to completely destroy your average bridge.
0:02:54 > 0:03:01Back in 2008 the bridge was hit by a tremor.
0:03:05 > 0:03:10The shaking ground had caused buildings to collapse less than 15 miles away,
0:03:10 > 0:03:13killing two people and injuring many more.
0:03:17 > 0:03:21Amidst the chaos, the bridge survived unscathed,
0:03:21 > 0:03:25allowing emergency traffic to pass safely and quickly over the gulf.
0:03:25 > 0:03:28But surprisingly,
0:03:28 > 0:03:33shaking ground wasn't the first challenge earthquakes posed to the bridge builders.
0:03:33 > 0:03:39Before they could start, they had to deal with what lay at the bottom of the sea.
0:03:42 > 0:03:47For the engineers, this was always going to be a bridge over troubled waters.
0:03:47 > 0:03:50Yeah, I know, sorry. But it was!
0:03:50 > 0:03:53Just getting started was going to be a huge engineering challenge.
0:03:53 > 0:03:58In fact, when they began, they still didn't know how they were going to lay their foundations.
0:03:58 > 0:04:01The sea here is 65 metres deep,
0:04:01 > 0:04:08a challenge in itself, but at the bottom there's nothing but sand and silt for hundreds of metres down.
0:04:08 > 0:04:14There's no solid bedrock and no solid bedrock means no solid foundations.
0:04:17 > 0:04:22Solid foundations are, of course, crucial to any structure,
0:04:22 > 0:04:26especially when they're shaken by frequent earthquakes.
0:04:26 > 0:04:30Combining a sandy seabed with seismic activity results
0:04:30 > 0:04:36in a relatively little-known danger from earthquakes called liquefaction.
0:04:36 > 0:04:44In a tremor, soft, wet ground literally turns to liquid, which really is as bad as it sounds.
0:04:46 > 0:04:52Nobody in the world had ever before set out to build a bridge in these conditions.
0:04:52 > 0:04:57The engineers came up with the solution that seems to defy logic.
0:04:57 > 0:05:02But first, why does a tremor turn sand and water into a liquid?
0:05:02 > 0:05:07I've created an earthquake machine to replicate the conditions
0:05:07 > 0:05:10at the bottom of the Gulf of Corinth.
0:05:10 > 0:05:13This engine is going to play the part of an earthquake.
0:05:15 > 0:05:20The sand and water can play themselves, and to get a bone-shaking feel for the problem,
0:05:20 > 0:05:24I'll be the bridge itself.
0:05:24 > 0:05:28If you add an earthquake to loose, wet ground,
0:05:28 > 0:05:31something pretty strange can happen, as I shall now demonstrate.
0:05:31 > 0:05:33Here we have the loose, wet ground.
0:05:33 > 0:05:36It's sand with water but it's solid enough.
0:05:36 > 0:05:37Standing in here quite happily.
0:05:37 > 0:05:41OK, if we're ready then, chaps, take it away.
0:05:45 > 0:05:47Now, my earthquake is starting.
0:05:48 > 0:05:52It is really very loud and very shaky.
0:05:52 > 0:05:57Straightaway I see water coming to the top.
0:05:59 > 0:06:01In fact, I think I'm starting to sink.
0:06:03 > 0:06:04That's a lot of water.
0:06:16 > 0:06:22Clearly, what's happened is - apart from being deafened - I've sunk.
0:06:22 > 0:06:28It isn't just that the water's on the top. I mean, I really have... I'm in the ground.
0:06:28 > 0:06:30So I need to find out what's happened.
0:06:30 > 0:06:35To do that, I need to get out and that's not very easy.
0:06:35 > 0:06:37Hold on!
0:06:38 > 0:06:40Yep.
0:06:40 > 0:06:45Obviously, in the Western movie version of this, I'd get my horse
0:06:45 > 0:06:51by the side of the quicksand and he'd pull me out. OK.
0:06:53 > 0:06:59The ground holds me up fine before the earthquake, then it turns into quicksand.
0:06:59 > 0:07:04As it's shaken, the whole thing changes from solid to liquid.
0:07:04 > 0:07:06It liquefies and I sink.
0:07:09 > 0:07:15'Geo-technical engineer Stuart Haigh explains that the key is that the sand is wet.'
0:07:15 > 0:07:19When the sand particles are shaken, the spaces in between them,
0:07:19 > 0:07:23or the pores, try and get smaller, the water in there gets squashed and the pressure goes up.
0:07:23 > 0:07:28Once that happens, whatever's standing on top of it sinks into the ground.
0:07:31 > 0:07:35Combine wet sand with seismic shocks and it's a killer.
0:07:35 > 0:07:41When a huge earthquake hit Kobe Harbour, Japan,
0:07:41 > 0:07:45in 1995, over 6,000 people died.
0:07:45 > 0:07:49It measured 7.2 on the Richter Scale.
0:07:49 > 0:07:53Sure enough, the ground was sandy and full of water.
0:07:53 > 0:07:59When the mix was shaken and stirred, the result was catastrophic liquefaction.
0:07:59 > 0:08:02Literally the previously solid ground became liquid.
0:08:05 > 0:08:13Ordinarily, engineers can drain the sand to get rid of the water or compact it
0:08:13 > 0:08:14so that the water is squeezed out.
0:08:18 > 0:08:21None of this was possible in the Gulf of Corinth
0:08:21 > 0:08:28and the sand to compact up to 1,640 feet deep.
0:08:28 > 0:08:30An impossible task.
0:08:32 > 0:08:35There was no solution in the bridge builders' manual,
0:08:35 > 0:08:38so the Rion designers had to come up with their own, which they did,
0:08:38 > 0:08:40thanks to incense.
0:08:40 > 0:08:45This is vetiver grass and it's used to make incense thanks to a sweet-smelling volatile oil
0:08:45 > 0:08:47in the roots.
0:08:47 > 0:08:49But it wasn't the oil they were after.
0:08:58 > 0:09:03These are the roots, hanging down in here.
0:09:03 > 0:09:10These contain an oil that really does smell lovely.
0:09:10 > 0:09:17Now, this grass originates in swamps in India, so harvesting it was horribly difficult.
0:09:17 > 0:09:19Snakes and awful conditions.
0:09:19 > 0:09:25The growers soon learned to grow it in places more convenient for harvesting - on riverbanks.
0:09:25 > 0:09:32They then noticed that these roots, which can grow up to seven metres long in fully-grown plants,
0:09:32 > 0:09:37stabilised the soft ground they were growing in.
0:09:37 > 0:09:40That's what interested the bridge designers.
0:09:42 > 0:09:47The way that the long, thin roots of the vetiver grass stabilised riverbanks
0:09:47 > 0:09:50worked for the bridge engineers too.
0:09:52 > 0:09:57With my own earthquake rig, I'm going to put their solution to the test.
0:09:59 > 0:10:03Here you go, Jim. Is this it?
0:10:03 > 0:10:07- That's it.- And just this many? I've got, what, six of them? - Six will be fine.
0:10:07 > 0:10:11And it's going to be an earthquake of the same strength as before?
0:10:11 > 0:10:17OK, well, I'm going to trust you and your theory and I'm not going to put my waders back on.
0:10:17 > 0:10:20I'm going to go in. I shall wear just my new boots.
0:10:20 > 0:10:22- You'll be fine.- Really?- Yep.
0:10:24 > 0:10:30It's not that I can't sink - the rods don't actually touch the bottom of the tank -
0:10:30 > 0:10:33They work because they reduce movement in the sand.
0:10:33 > 0:10:40So they should stop my board from sinking and my new boots should stay new.
0:10:40 > 0:10:43All right. Let's do it.
0:10:43 > 0:10:45Don't ruin my new boots.
0:10:45 > 0:10:47Go.
0:10:47 > 0:10:49Whoa!
0:10:59 > 0:11:03I'm not going any further.
0:11:09 > 0:11:13After some initial settling, it does the job.
0:11:13 > 0:11:18So by sinking steel rods into the seabed, the engineers managed to stabilise it.
0:11:18 > 0:11:23Actual vetiver grass is used to stabilise river banks and cliffs edges across the world,
0:11:23 > 0:11:27from Africa to Fiji. Those long, thin roots hold the soil together.
0:11:31 > 0:11:35Beneath three of the four piers of the Rion-Antirion Bridge
0:11:35 > 0:11:39are 200 metal piles driven into the sand.
0:11:39 > 0:11:41They're just like my small ones in the skip,
0:11:41 > 0:11:46but here each pile is huge - at least 25 metres long.
0:11:46 > 0:11:49They still don't reach the bedrock.
0:11:49 > 0:11:53Even more surprising, the bridge doesn't rest on these piles.
0:11:53 > 0:11:58The tops of the piles are almost a metre beneath the base of the piers,
0:11:58 > 0:12:04but they're enough to keep the sand from liquidising, even in an earthquake.
0:12:04 > 0:12:09The bridge won't sink. This solution had never been used before.
0:12:09 > 0:12:11Until the construction of this bridge,
0:12:11 > 0:12:16building on wet sand in an earthquake zone was obviously a big no-no.
0:12:16 > 0:12:21But thanks to a fragrant gift from Mother Nature, the engineers came up smelling of roses.
0:12:21 > 0:12:23Well, vetiver grass.
0:12:25 > 0:12:30Even though the entire weight of the bridge is held up by just these four piers,
0:12:30 > 0:12:36the engineers had succeeded in keeping them from sinking into the ground in an earthquake.
0:12:36 > 0:12:40As soon as they'd solved one problem here, another one came up.
0:12:40 > 0:12:43They could stop the piers from sinking in an earthquake,
0:12:43 > 0:12:46but how could they stop them from toppling over?
0:12:51 > 0:12:55In an earthquake, the earth moves vigorously from side to side
0:12:55 > 0:12:59and would take the gigantic piers with it.
0:12:59 > 0:13:03That could be a big problem for a big bridge.
0:13:05 > 0:13:09Phil Corbett has offered to take me a bit closer to the problem.
0:13:09 > 0:13:15The piers are actually hollow, so I'm going to go right down to the bottom of them.
0:13:15 > 0:13:18This is just the first floor down and I'm starting to get
0:13:18 > 0:13:20a real sense of what I've taken on.
0:13:20 > 0:13:23Ooh!
0:13:23 > 0:13:27That's the centre of the earth. It must be.
0:13:29 > 0:13:34Well, it is a nerve-racking 110 metres down in total.
0:13:34 > 0:13:38There can't be that much further to go now, surely?
0:13:38 > 0:13:40Then, just when I thought I'd reached the bottom...
0:13:45 > 0:13:50Well, I've been climbing down ladders and stairs for what felt like weeks
0:13:50 > 0:13:54and this is all I've done. Sea level.
0:13:54 > 0:14:01There's a whole lot more to come because this thing goes on and on and on down there.
0:14:05 > 0:14:0933 flights of stairs later...
0:14:09 > 0:14:11This is it, then. Bottom of the sea.
0:14:11 > 0:14:1765 metres above is the surface of the sea. Under there, the bed.
0:14:17 > 0:14:23These are the biggest bridge piers of their kind in the world.
0:14:23 > 0:14:31This one weighs 171,000 tonnes and from down here to the top, it's about 30 storeys.
0:14:31 > 0:14:3490 metres across at the base of this thing.
0:14:34 > 0:14:39In an earthquake - it is almost impossible to imagine -
0:14:39 > 0:14:47to keep it from falling over, this whole gigantic tower needs to move freely from side to side.
0:14:50 > 0:14:55If the base got stuck, the whole thing would topple over.
0:14:55 > 0:15:00The engineers need to make sure that each pier can move freely.
0:15:00 > 0:15:02So what to do?
0:15:02 > 0:15:06The answer to that lies in an age-old winter pastime.
0:15:09 > 0:15:14The Rion-Antirion Bridge has one thing in common with winter sports.
0:15:14 > 0:15:17They both involve moving freely - sliding.
0:15:20 > 0:15:23Of course, tempting as it is...
0:15:23 > 0:15:25I didn't come here to play in the snow.
0:15:31 > 0:15:38Just like a toboggan, the bridge piers have to slide freely over the sea floor which is made of sand.
0:15:38 > 0:15:42But they don't slide well on sand because of their shape.
0:15:45 > 0:15:50To show you what I mean, this board is flat, like the bottom of the bridge pier.
0:15:58 > 0:16:03Yeah. The problem is the leading edge is digging in, or toeing in, as they say in the trade.
0:16:03 > 0:16:04It won't go anywhere.
0:16:04 > 0:16:06That could have been a real problem for the Rion Bridge.
0:16:08 > 0:16:13Sliding down a hill of loose sand is one thing, but does a pier
0:16:13 > 0:16:17on the flat seabed really have the same problem?
0:16:17 > 0:16:23I've got myself an accurate scale model of a bridge pier.
0:16:23 > 0:16:25Well, give or take a few hundred metres.
0:16:25 > 0:16:28It's currently being supported without a problem
0:16:28 > 0:16:32by this ultra-smooth track of fine sand.
0:16:32 > 0:16:36This time, to create the effect of the ground moving sideways,
0:16:36 > 0:16:41or laterally, the role of the earthquake will be played by a 4x4.
0:16:43 > 0:16:49I've also brought along Ian Price, an expert in stabilising soils.
0:16:49 > 0:16:54So even though we're not at the bottom of the sea, by any means, you reckon this is
0:16:54 > 0:17:00- a good representation of what might happen 65 metres down?- Yeah, we're attempting to simulate that effect.
0:17:00 > 0:17:04OK. So I'm going to drive away because this is a lateral force we're talking about?
0:17:04 > 0:17:06We're talking about large lateral forces.
0:17:06 > 0:17:10- This is a large lateral force. - I'm going to stand well clear.
0:17:10 > 0:17:14OK, I'm going to create an earthquake.
0:17:23 > 0:17:24Ah.
0:17:29 > 0:17:32My pier fell over.
0:17:32 > 0:17:35- So this is the toeing in you're talking about?- That's right.
0:17:35 > 0:17:37Why did it fall? Why didn't it just keep following me?
0:17:37 > 0:17:43The weight overcame the ability of the sand to support the structure.
0:17:45 > 0:17:50In an earthquake, the piers of the Rion Bridge would be pushed sideways, like this.
0:17:50 > 0:17:55As it moves, the leading edge puts more pressure on the sand beneath it
0:17:55 > 0:17:58until it's more than the sand can support.
0:17:58 > 0:18:03It digs or toes in, and then it topples over.
0:18:04 > 0:18:07Really not what you want.
0:18:07 > 0:18:14So the key is how much pressure from the leading edge a material can support.
0:18:14 > 0:18:17In winter sports, the solution is simple.
0:18:17 > 0:18:20Take away the leading edge altogether.
0:18:20 > 0:18:24Make your skis, snowboard or toboggan curl up at the front.
0:18:32 > 0:18:36That's fine for a toboggan, but making mammoth pier bases
0:18:36 > 0:18:41that curl up like giant sleds would be virtually impossible to construct.
0:18:41 > 0:18:44They needed another solution.
0:18:46 > 0:18:50The one they chose was extreme.
0:18:52 > 0:18:57Rather than change the shape of the piers, they decided to change the surface of the seabed.
0:19:00 > 0:19:06For their solution, the bridge engineers needed to understand why you toe in to soft material.
0:19:07 > 0:19:10I've got to ask, why is there a paddling pool
0:19:10 > 0:19:13full of what appears to be mashed potato?
0:19:13 > 0:19:20Well, this demonstrates what the engineers found on the site of the Rion-Antirion Bridge.
0:19:20 > 0:19:27What we have there is silts and clays which are very, very soft, very analogous to mashed potato.
0:19:27 > 0:19:31There's no way that sands will support the weight of the structure. Try it yourself, Richard.
0:19:31 > 0:19:35- What, get in?- Yeah. Why not? - All right, fair enough.
0:19:35 > 0:19:39This is not something I've done before. So I'm the bridge.
0:19:39 > 0:19:42Clearly, mashed potato isn't going to be up to the job.
0:19:44 > 0:19:48Yeah, mash is obviously too soft to support me.
0:19:48 > 0:19:51But there is a way that exactly the same stuff can support more pressure.
0:19:51 > 0:19:55- These, then, are just potatoes?- They are.
0:19:55 > 0:20:00And they work perfectly They'll support me.
0:20:00 > 0:20:03So obviously those potatoes are mashed and these aren't,
0:20:03 > 0:20:07but they're still a paddling pool of potatoes. What's the difference?
0:20:07 > 0:20:09The difference is particle size.
0:20:09 > 0:20:15Potatoes are a larger particle size and consequently you will get increased bearing resistance.
0:20:15 > 0:20:16So just the bigger particle size.
0:20:16 > 0:20:21Same material, but smaller particles of it over there and I sink through them,
0:20:21 > 0:20:23- bigger particles here and they can hold up more weight?- That's right.
0:20:23 > 0:20:26So the answer to the bridge builders' problems was potatoes.
0:20:26 > 0:20:31Well, not exactly potatoes, but a larger particle size - gravel.
0:20:33 > 0:20:36So gravel was just what the engineers needed.
0:20:38 > 0:20:42Instead of changing the shape of the piers to make them curl up at the edges,
0:20:42 > 0:20:48they changed the seabed with a layer of gravel. A huge job.
0:20:51 > 0:20:58I'm going to create another 4x4 earthquake and put the pier on a gravel base.
0:20:58 > 0:21:03It should support the leading edge so it won't toe in and fall over.
0:21:06 > 0:21:09So the only change this time is we're replacing sand with gravel?
0:21:09 > 0:21:11- Yes. - This will make all the difference?
0:21:11 > 0:21:14- Yes.- You reckon?- I think so. - I'll bring on an earthquake.
0:21:14 > 0:21:15Stand back.
0:21:24 > 0:21:28- That made all the difference. - It did.- So it does work.
0:21:28 > 0:21:34The answer for the engineers was to build their bridge on un-mashed potatoes. Well, no. Gravel.
0:21:34 > 0:21:37At the bottom of the Gulf of Corinth,
0:21:37 > 0:21:42the Rion Bridge rests on a thick layer of gravel above the steel rods.
0:21:44 > 0:21:47This allows the bridge piers to slide from side to side
0:21:47 > 0:21:50without digging or toeing in.
0:21:50 > 0:21:53They used enough gravel on the seabed
0:21:53 > 0:22:00beneath the Rion-Antirion Bridge to cover two football pitches three metres deep.
0:22:01 > 0:22:05These massive piers are amazing.
0:22:05 > 0:22:08They stand strong but without being fixed to the seabed,
0:22:08 > 0:22:11so they can move and withstand earthquakes.
0:22:12 > 0:22:18The piers really are awesome but they're obviously only part of the story.
0:22:18 > 0:22:24Their purpose is to hold up the bridge deck, which is what it's all about.
0:22:24 > 0:22:29The deck has four lanes as well as two safety lanes
0:22:29 > 0:22:34that run for almost two miles in each direction.
0:22:35 > 0:22:37It's mammoth.
0:22:37 > 0:22:40If the engineers fixed it to any of the piers and those piers then
0:22:40 > 0:22:44moved in an earthquake, which the gravel allows them to do,
0:22:44 > 0:22:46it could buckle
0:22:46 > 0:22:49or break. Not good.
0:22:53 > 0:22:57Right, what we need now is another one of my earthquake demonstrations.
0:22:57 > 0:22:59This one is going to require a little imagination.
0:22:59 > 0:23:05Bear with me. This is my road deck, which I'm going to fit to this boat.
0:23:05 > 0:23:09But for the purposes of this, the boat represents the piers of the bridge.
0:23:09 > 0:23:15So that's the piers supporting the road deck, concrete and steel, fixed to it solidly.
0:23:15 > 0:23:17Now we're going to have an earthquake.
0:23:17 > 0:23:21I need muscle so I'm going to break out the Herefordshire Special Ballet Squad.
0:23:21 > 0:23:23In you come, then, lads, please. Come on.
0:23:23 > 0:23:26They'll be the muscle to make the earthquake.
0:23:26 > 0:23:30I'm going to be the traffic on the road deck, fixed solidly to the piers.
0:23:30 > 0:23:35So, getting into place. I'm the traffic on the deck.
0:23:35 > 0:23:39Oh, no, I hope there isn't an earthquake shortly.
0:23:39 > 0:23:41Go on, lads, let it rip.
0:23:55 > 0:23:57As an experience, it's unpleasant,
0:23:57 > 0:24:02but if this were a road deck on a bridge and I were heavy traffic on it,
0:24:02 > 0:24:08clearly the stresses that the materials would be subject to would be catastrophic.
0:24:08 > 0:24:10It's not going to work.
0:24:10 > 0:24:13One earthquake, the whole thing could collapse.
0:24:21 > 0:24:25To save the bridge deck from the violent and chaotic movements of an earthquake,
0:24:25 > 0:24:30the engineers needed to build it in a way that allowed it
0:24:30 > 0:24:36to move independently of the piers, which is where sailors and their sleeping arrangements come in.
0:24:38 > 0:24:44Christopher Columbus first encountered hammocks in South America
0:24:44 > 0:24:47and he brought them back to Europe.
0:24:47 > 0:24:51Early sailors very quickly discovered that they were quite handy things
0:24:51 > 0:24:56for making life more bearable on board because, well,
0:24:56 > 0:25:00ships weren't the most sophisticated of devices then. Things could get pretty rough,
0:25:00 > 0:25:06but no matter how rough the seas, the hammock would isolate them from the movements of the ship
0:25:06 > 0:25:10and make life just about bearable.
0:25:10 > 0:25:12They didn't know it, but in fact a hammock
0:25:12 > 0:25:16is a kind of pendulum and it has a steady rate it wants to move at,
0:25:16 > 0:25:18which it will do regardless of what's going on around it.
0:25:18 > 0:25:22And it meant that sailors were more comfortable.
0:25:22 > 0:25:26What's good enough for them is actually good enough for the bridge.
0:25:29 > 0:25:36So just as a pendulum, or rather a hammock, swings gently on board a ship in rough seas,
0:25:36 > 0:25:41it ought to make my ride on the earthquake simulator a bit smoother, too.
0:25:43 > 0:25:45Here is my modified bridge.
0:25:45 > 0:25:48Remember, the boat represents the bridge piers, the structure.
0:25:48 > 0:25:53This hammock now represents the deck slung between them.
0:25:53 > 0:25:59Right, I need to break out the boys to hold the bridge steady first of all, please.
0:25:59 > 0:26:02Then I hope there isn't another earthquake.
0:26:02 > 0:26:07Right, I'm getting onto the road deck, which now is slung, pendulum style, just like a hammock.
0:26:09 > 0:26:13Goodness, what if an earthquake were to occur right now when I'm on the bridge?
0:26:13 > 0:26:15Actually it is already.
0:26:15 > 0:26:20Straightaway, what's happening here is the hammock,
0:26:20 > 0:26:26the pendulum suspension, is isolating me from the movement of the piers.
0:26:26 > 0:26:29Even when things get pretty bad.
0:26:29 > 0:26:34I mean, this is a pretty disastrous earthquake we're experiencing right now.
0:26:34 > 0:26:41The pendulum is turning chaotic movement into something a bit more predictable
0:26:41 > 0:26:43and a lot more gentle.
0:26:45 > 0:26:49I can imagine, straightaway, how this would stay standing.
0:26:56 > 0:27:02The Rion engineers borrowed that same pendulum principle to help earthquake-proof their bridge.
0:27:02 > 0:27:09Just like a hammock, the deck of the Rion Bridge is fully suspended from the top of the piers.
0:27:10 > 0:27:12It's unique in all the world.
0:27:15 > 0:27:21Incredibly, as the piers move in an earthquake, the deck swings independently.
0:27:21 > 0:27:25It seemed, yet again, the engineers had tamed the earthquake,
0:27:25 > 0:27:29but their free-swinging solution might itself have created a problem.
0:27:32 > 0:27:34The deck can swing freely,
0:27:34 > 0:27:37but if it swings too far in either direction,
0:27:37 > 0:27:42it would smash into one of the four thin arms of the piers.
0:27:44 > 0:27:49That's 75,000 tonnes of road hitting the concrete,
0:27:49 > 0:27:53a big moving mass, and it could destroy the bridge.
0:27:53 > 0:27:56The engineers couldn't allow it to happen,
0:27:56 > 0:28:03but once an object as big as the road deck starts moving, it takes something extraordinary to stop it.
0:28:03 > 0:28:08Enter, the viscous damper, an ultra-powerful braking system.
0:28:15 > 0:28:21To experience a viscous damper first hand, I've devised a little experiment, a demonstration.
0:28:22 > 0:28:27First, I'm going to show what happens with no brakes, no viscous damper.
0:28:27 > 0:28:30That in front of me is a teeter-totter.
0:28:30 > 0:28:33Basically it's a giant seesaw.
0:28:33 > 0:28:40But this is no playground and that is a mighty big drop at the other side.
0:28:40 > 0:28:48And this, in my car, is a roll cage, just in case my confidence outstrips my skill.
0:28:48 > 0:28:51Right, all I've got to do is drive up there.
0:28:53 > 0:29:01It's my job to drive up it, past the pivot point and then let gravity do its worst.
0:29:04 > 0:29:08Of course, the higher I go, the further I'm going to fall.
0:29:08 > 0:29:10I'm not enjoying this at all.
0:29:12 > 0:29:18The pivot point must be somewhere about here.
0:29:18 > 0:29:23This is just horrible! I can't see a thing. I don't know where I'm going.
0:29:23 > 0:29:26At some point, I know that something bad is going to happen.
0:29:26 > 0:29:28That much is guaranteed.
0:29:30 > 0:29:34I can smell clutch. Ooh!
0:29:36 > 0:29:38That's not very...
0:29:44 > 0:29:46For the purposes of this demonstration,
0:29:46 > 0:29:52what just happened to my car as it hit the tarmac is the equivalent of the free-swinging bridge deck
0:29:52 > 0:29:55violently hitting the pier that holds it up during an earthquake.
0:29:55 > 0:29:59If the deck swung hard enough, it could break the bridge.
0:29:59 > 0:30:07The engineers needed to slow the deck movement and I need to stop the seesaw banging down so hard.
0:30:07 > 0:30:11We both need some brakes, which is where viscous damping comes in.
0:30:11 > 0:30:15It's a braking system where you use a liquid to resist movement.
0:30:15 > 0:30:20If you've ever tried to run in a swimming pool, you'll know all about the resistance water can create.
0:30:22 > 0:30:27This black box is going to be full of water and there's also a fan in there
0:30:27 > 0:30:32which will have to move through it, absorbing all the energy from the seesaw. It's a brake.
0:30:34 > 0:30:38This is a viscous damper. It's basically a liquid - in this case,
0:30:38 > 0:30:40water - that slows the movement.
0:30:40 > 0:30:42It should give me a softer landing.
0:30:42 > 0:30:44Only one way to find out.
0:31:06 > 0:31:11OK, any minute now we should reach balance point.
0:31:36 > 0:31:38Oh! Oh, this is lovely.
0:31:45 > 0:31:48That really does work perfectly.
0:31:48 > 0:31:52What happens is the vertical motion of the teeter-totter, of the seesaw,
0:31:52 > 0:31:56is slowed down by the rotary motion of the fan inside the liquid.
0:31:56 > 0:32:01Essentially what it does is turn some of that energy, that kinetic energy, into heat
0:32:01 > 0:32:07inside the damper, which gives me a much, much softer landing, kinder to my car.
0:32:13 > 0:32:17Viscous dampers are used all over the place to soften movement.
0:32:19 > 0:32:24These planes are coming in to land on an aircraft carrier in the middle of the ocean.
0:32:24 > 0:32:30They approach at over 100 miles an hour, but they can stop in such short distances
0:32:30 > 0:32:33thanks to viscous dampers that are attached
0:32:33 > 0:32:37to the catch wires stretched across the runway.
0:32:37 > 0:32:43And the bridge is fitted with its own incredible liquid safety system.
0:32:43 > 0:32:50These things that look like pistons are the viscous dampers and they're just like my system, in principle.
0:32:53 > 0:32:56This footage shows the dampers being tested.
0:32:56 > 0:33:00Instead of a fan spinning in water, a piston has to move through oil
0:33:00 > 0:33:03which is much thicker, or viscous, than water,
0:33:03 > 0:33:07so it offers much more resistance to movement.
0:33:07 > 0:33:11In infra-red you can see it heating up, so the liquid is
0:33:11 > 0:33:15turning all that kinetic energy - that movement - into heat.
0:33:17 > 0:33:21The viscous dampers on the bridge are the biggest in the world.
0:33:29 > 0:33:33Slinging the road deck like a hammock allows the bridge deck to move
0:33:33 > 0:33:37and the viscous dampers stop it from moving too much so it doesn't
0:33:37 > 0:33:41hit the arms of the piers and shake itself to bits.
0:33:45 > 0:33:50The designers made this extraordinary bridge uniquely earthquake-proof,
0:33:50 > 0:33:53with unprecedented solutions.
0:33:53 > 0:33:56But all this flexibility created a further problem
0:33:56 > 0:34:02because earthquakes aren't the only natural hazard in this region.
0:34:02 > 0:34:06Mother Nature has another trick up her sleeve.
0:34:07 > 0:34:14This narrow stretch of the Gulf of Corinth, with mountains on either side, makes a natural wind tunnel.
0:34:14 > 0:34:19A flexible bridge is good for withstanding earthquakes but it's bad when it's windy.
0:34:22 > 0:34:27Even with the dampers to soften the movement, near-constant winds in the gulf
0:34:27 > 0:34:31mean the bridge would be swaying constantly.
0:34:31 > 0:34:36An impossible choice, then, for the engineers. Make the bridge flexible enough to cope with an earthquake,
0:34:36 > 0:34:40and on normal days when there isn't an earthquake, it would swing so violently,
0:34:40 > 0:34:44it would be uncrossable thanks to the winds in the Gulf of Corinth.
0:34:44 > 0:34:48But make it strong enough to cope with the wind by fixing it firmly in place,
0:34:48 > 0:34:50and when there is an earthquake,
0:34:50 > 0:34:54it would snap and crumble into an 800-million-Euro pile of rubble.
0:34:54 > 0:34:58The answer to their conundrum lies in this, a fizzy-pop can.
0:35:02 > 0:35:06Engineers don't usually design things to fail.
0:35:06 > 0:35:09They build them to withstand the daily challenges they will face -
0:35:09 > 0:35:12to be strong and rugged and to stay that way.
0:35:14 > 0:35:19Helpfully for the Rion Bridge, an inventor threw away the usual rules of engineering
0:35:19 > 0:35:24after a frustrating picnic. He needed a new way of opening a can.
0:35:24 > 0:35:29The humble tin can has been around for 200 years.
0:35:29 > 0:35:35It can keep produce fresh for decades and transformed the food industry.
0:35:35 > 0:35:37They weren't designed for easy access.
0:35:37 > 0:35:40Getting into them required some muscle.
0:35:47 > 0:35:52That changed when inventor Ermal Fraze came up with a new way of opening them,
0:35:52 > 0:35:58which revolutionised cans and protects the Rion Bridge.
0:35:58 > 0:36:02Yep, this is a real picnic, just on my own.
0:36:02 > 0:36:07Ermal Fraze found himself on a picnic with a canned drink
0:36:07 > 0:36:10but someone had forgotten to pack the can opener.
0:36:10 > 0:36:15Being a resourceful sort of chap, he managed to wrestle it open on his car bumper
0:36:15 > 0:36:17but that took all the chrome off the bumper.
0:36:17 > 0:36:20So he went away and thought about the problem
0:36:20 > 0:36:25and he devised the pull tab, precursor to today's stay tab.
0:36:25 > 0:36:32This weak section here is designed to be strong enough to keep the fizzy drink contained within,
0:36:32 > 0:36:35but weak enough so that by hand, without any sort of machine,
0:36:35 > 0:36:40you can just rip it open. This has to fail at a set limit.
0:36:40 > 0:36:42It has to fail predictably.
0:36:43 > 0:36:51Ah, yep. And it does. I have made a bit of a mess of my picnic though.
0:36:55 > 0:36:56In the right place,
0:36:56 > 0:37:01making something fail predictably can be the difference between life and death.
0:37:03 > 0:37:06For instance, you might recently have reorganised your workshop
0:37:06 > 0:37:09and tidied away a load of cardboard boxes into a corner
0:37:09 > 0:37:13and then, inexplicably, soaked them in petrol, for some reason,
0:37:13 > 0:37:19and then decided to catch up on that bit of angle grinding you've been meaning to get to for so long.
0:37:27 > 0:37:30Oh, no. There's a fire!
0:37:30 > 0:37:35That could be a real problem without predictable failure,
0:37:35 > 0:37:38which is what's just happened.
0:37:38 > 0:37:40This is a sprinkler system.
0:37:40 > 0:37:45I installed it myself, which is fortunate because I'd forgotten where I'd put the fire extinguisher.
0:37:45 > 0:37:48It's pretty much exactly the same as the sprinkler system
0:37:48 > 0:37:51in schools and buildings across the world but it's a lot uglier.
0:37:51 > 0:37:53It works in exactly the same way.
0:38:02 > 0:38:06Disaster averted and here's how it works.
0:38:06 > 0:38:10This is the sprinkler system and the job it's got to do sounds pretty complicated.
0:38:10 > 0:38:14It's got to automatically detect a fire and then automatically put it out.
0:38:14 > 0:38:17But the way it does that is pretty simple.
0:38:17 > 0:38:20This is the kind of thing you will have seen sticking out of the ceiling
0:38:20 > 0:38:22in offices, shops and schools.
0:38:22 > 0:38:25These are connected to a water pipe along here.
0:38:25 > 0:38:29Now, before they've been triggered, they feature this little glass vial.
0:38:29 > 0:38:34This has been designed so that at 68 degrees it breaks.
0:38:34 > 0:38:39The red liquid boils at exactly 68 degrees.
0:38:39 > 0:38:44That makes the pressure inside high enough to break the glass.
0:38:47 > 0:38:49That's the predictable failure.
0:38:49 > 0:38:52They can predict - 68 degrees, that goes.
0:38:52 > 0:38:55When that happens, that falls away and it opens up the hole,
0:38:55 > 0:38:59here, so the water can just flood out, hit that disk and form the sprinkler effect,
0:38:59 > 0:39:02putting the fire out automatically.
0:39:02 > 0:39:06And it's all thanks to a predictable failure in there.
0:39:06 > 0:39:11Engineers have adopted the pop-can principle of predictable failure
0:39:11 > 0:39:15all over the place to help us go about our daily lives safely.
0:39:15 > 0:39:16Think circuit breakers,
0:39:16 > 0:39:23such as fuses that cut out when electrical circuits overload, or car airbags that inflate in an accident.
0:39:23 > 0:39:29Life goes on normally, but we are protected the moment something changes.
0:39:33 > 0:39:37So how does predictable failure help the bridge against winds?
0:39:37 > 0:39:43You stop the bridge moving unless it's struck by a massive shock.
0:39:43 > 0:39:49You don't allow wind pressure to swing it, but it breaks free and protects itself in an earthquake.
0:39:53 > 0:39:58Dr Papanikolas showed me how the combination of the fizzy-pop can theory
0:39:58 > 0:40:01and the viscous dampers keep the bridge safe.
0:40:01 > 0:40:05So where are the predictable failures in here, then?
0:40:05 > 0:40:08Because it all looks massive and solid.
0:40:08 > 0:40:14OK. What you have here is the deck. It is laterally supported
0:40:14 > 0:40:18by the dampers. In the middle one you have what we call a strut.
0:40:18 > 0:40:21Oh, so that solves the problem of the wind?
0:40:21 > 0:40:25If you think, every day, you don't want the bridge to swing back and forth.
0:40:27 > 0:40:31Inside each strut, there's a so-called fuse.
0:40:31 > 0:40:35It's designed to break at a set limit, just like a ring-pull.
0:40:35 > 0:40:38When the load gets too big, it fails.
0:40:38 > 0:40:41The fuses can take the load of even the strongest winds,
0:40:41 > 0:40:43but when an earthquake hits and the load exceeds
0:40:43 > 0:40:49the pre-set limit, they break and those huge viscous dampers start to work.
0:40:51 > 0:40:53This isn't just theory.
0:40:53 > 0:40:57This CCTV footage caught the action in June 2008.
0:40:57 > 0:41:02A magnitude 6.5 earthquake hit the bridge, the fuse snapped,
0:41:02 > 0:41:07and the dampers sprang into action. It worked.
0:41:07 > 0:41:13So as designers, as engineers, seeing your creation actually work
0:41:13 > 0:41:17and do what you always knew it would do, but actually seeing it for real,
0:41:17 > 0:41:19must have been amazing.
0:41:19 > 0:41:21Yes, it's an unbelievable feeling.
0:41:21 > 0:41:24This is the feeling of engineering.
0:41:24 > 0:41:31An earthquake- and wind-proof bridge, all thanks to predictable failure,
0:41:31 > 0:41:35courtesy of Ermal Fraze's easy-open drinks can.
0:41:38 > 0:41:41Well, that covers just about everything. Foundations?
0:41:41 > 0:41:43Earthquake-proofed. Check.
0:41:43 > 0:41:51Piers, the deck? Earthquake- and wind-proofed. Check. Oh, no, hold on, we've forgotten something.
0:41:51 > 0:41:54The cables.
0:41:54 > 0:41:58Believe it or not, the same cables that hold the road deck
0:41:58 > 0:42:02could pose a mortal threat to the bridge.
0:42:02 > 0:42:10Not because of earthquakes, not even because of gale-force winds. Just a gentle breeze can be lethal.
0:42:12 > 0:42:18Over 6,000 miles away, in Baytown, Texas, the cables of the Fred Hartman Bridge
0:42:18 > 0:42:21began to look a lot less than solid.
0:42:21 > 0:42:25Spring 1997, two years after the bridge opened.
0:42:25 > 0:42:33In winds as low as 10 miles an hour, the cables bounced up and down ferociously.
0:42:33 > 0:42:35This happened time and time again.
0:42:35 > 0:42:40The structure suffered 100 separate stress failures, which could have been disastrous.
0:42:40 > 0:42:45Fortunately, the Texas Department of Transportation had been alerted
0:42:45 > 0:42:48and fixed it by tying all the cables together,
0:42:48 > 0:42:50holding each other down.
0:42:53 > 0:42:56The same conditions that threatened the Fred Hartman Bridge
0:42:56 > 0:43:00are a risk to any lightweight, round metal structure
0:43:00 > 0:43:04such as a cable, a tower or a chimney.
0:43:04 > 0:43:10The Emley Moor TV mast in Yorkshire was constructed in 1964,
0:43:10 > 0:43:17one of a new generation of lightweight structures built of metal rather than brick.
0:43:17 > 0:43:23In 1969, in light winds, the tower collapsed without warning.
0:43:23 > 0:43:30Ice buildup was blamed initially, but British aerodynamicist Kit Scruton
0:43:30 > 0:43:34knew it was due to a bizarre aerodynamic effect.
0:43:34 > 0:43:36It's called vortex shedding.
0:43:36 > 0:43:40That's nowhere near as difficult to understand as it sounds like it's going to be.
0:43:40 > 0:43:46To demonstrate, I've got a fan and that metal pole over there.
0:43:46 > 0:43:48So let's make it a windy day.
0:43:58 > 0:44:02That vibration is caused by swirls of air.
0:44:03 > 0:44:08This specially shot footage shows exactly what's happening.
0:44:08 > 0:44:11You can see the swirls moving from side to side.
0:44:11 > 0:44:14That's called vortex shedding.
0:44:14 > 0:44:17Any round structure creates these swirls of air which can
0:44:17 > 0:44:20pull it one way and then the other.
0:44:22 > 0:44:26You've got to remember, of course, that that's not the wind buffeting it,
0:44:26 > 0:44:28it's not gusting that's causing that shaking to happen,
0:44:28 > 0:44:31it's one vortex being shed after another, after another, that makes
0:44:31 > 0:44:37it vibrate like that. A further problem there is that if this goes on long enough, shaking and shaking
0:44:37 > 0:44:42and shaking, the metal itself will fatigue. It can be a catastrophic failure.
0:44:44 > 0:44:50It moves towers from side to side and it can move cables on bridges up and down,
0:44:50 > 0:44:54as the Fred Hartman Bridge in Texas can testify.
0:44:57 > 0:45:00Fortunately, British aerodynamicist Kit Scruton worked out
0:45:00 > 0:45:05how to overcome the lethal threat from vortex shedding.
0:45:06 > 0:45:10He invented the helical strake.
0:45:10 > 0:45:15A helical strake is a strip of metal that winds like a big coil spring around the top
0:45:15 > 0:45:17of tall steel towers today.
0:45:17 > 0:45:18It keeps them safe
0:45:18 > 0:45:22from the powers of vortex shedding.
0:45:22 > 0:45:26Yep. Now, I know what it looks like I've done is tied
0:45:26 > 0:45:29blue string around another tower, but this is more than that.
0:45:29 > 0:45:31This is a helical strake.
0:45:33 > 0:45:37The theory runs, what this does is, as the wind arrives at the structure,
0:45:37 > 0:45:40instead of a vortex forming the length of it,
0:45:40 > 0:45:44rolling around and shedding, and then another one and then another one,
0:45:44 > 0:45:48which sets up that movement, it breaks those vortices up.
0:45:48 > 0:45:52That simple act, breaking them up and changing the time at which they come around,
0:45:52 > 0:45:53evens the whole process out.
0:45:53 > 0:45:56No vibration, no failure of the structure.
0:45:56 > 0:45:59That's the theory. Now I'm going to make it windy and test it.
0:46:22 > 0:46:26So my blue string - helical strake - works.
0:46:26 > 0:46:30And now you can see them everywhere -
0:46:30 > 0:46:32just take a look next time you're out.
0:46:32 > 0:46:38And back on the Rion-Antirion Bridge, every cable is fitted with one of Kit Scruton's
0:46:38 > 0:46:41helical strakes. They break up the wind
0:46:41 > 0:46:44hitting the cables to protect the bridge from vortex shedding.
0:46:51 > 0:46:55On top of everything else, to accommodate for the fact that Rion
0:46:55 > 0:47:00is moving away from Antirion, the bridge has the largest
0:47:00 > 0:47:05expansion joints in the world, allowing for the two coasts to drift
0:47:05 > 0:47:09five metres away from each other.
0:47:09 > 0:47:14Now, what have they done to protect against possible meteor strikes?
0:47:14 > 0:47:15Well, it's a thought.
0:47:19 > 0:47:24The Rion-Antirion Bridge achieved what was previously impossible.
0:47:26 > 0:47:30In an active earthquake zone and natural wind tunnel,
0:47:30 > 0:47:33and without bedrock for foundations,
0:47:33 > 0:47:39the engineers created a magnificent design that overcame each of these hurdles.
0:47:40 > 0:47:45Remarkably, despite the need for unprecedented engineering solutions,
0:47:45 > 0:47:53the bridge opened four months ahead of schedule, fulfilling a century-old dream.
0:47:53 > 0:47:58Now it's part of the daily life of the people of Rion and Antirion,
0:47:58 > 0:48:03but the effect has been felt far beyond these two small towns
0:48:03 > 0:48:07because it has effectively redrawn the map of Greece.
0:48:07 > 0:48:12None of it would have been possible without a hammock...
0:48:12 > 0:48:13Go on, lads, let it rip.
0:48:16 > 0:48:18..some Indian incense,
0:48:18 > 0:48:24a steel chimney, the principles of tobogganing...
0:48:24 > 0:48:27and a fizzy-pop can.
0:48:27 > 0:48:30This is lovely.
0:48:30 > 0:48:34Oh, no. There's a fire!
0:48:34 > 0:48:37Subtitles by Red Bee Media Ltd
0:48:37 > 0:48:40E-mail subtitling@bbc.co.uk