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Officially, this suspension bridge over the River Lee, in Cork,
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in the south of Ireland, is called "Daly's Bridge",
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after a businessman who helped fund it back in the 1920s.
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But unofficially, it has a different name: the Shakey Bridge.
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Because it shakes.
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I was going to film this with my GoPro on a stick walking across,
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but it's a really narrow bridge,
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and I don't want to end up barging into the people who are actually using it.
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I can confirm from a brief experiment, though...
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Yep. It's bouncy!
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- In the early 1700s, there was a ferry boat that actually brought people from here
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across to the other side.
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But unfortunately between 1906 and 1908, the Dooley family actually retired,
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retired themselves from the ferry boat industry.
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And it was through the philanthropy of a man called James Daly, who gave
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nearly £700 towards the construction of a bridge project.
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£700 in today's terms would be around €50,000.
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And to be honest,
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you would not be able to build a bridge in today's world for €50,000.
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So the bridge was good value.
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David Rowell and Company, in London, Westminster,
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actually had a bridge catalogue.
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And the Corporation of Cork bought a bridge off the catalogue,
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and in early 1927 these huge, giant wooden boxes
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arrived on the banks of the River Lee.
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And the bridge actually was constructed.
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So in the first couple of months the people of the area
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discovered that the bridge actually shook when they walked over it.
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- Now, all suspension bridges, actually, pretty much all bridges,
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will move or shake or sway a little
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as the dynamic loads on them from people and weather change.
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And that's a good thing: because if they don't move a little...
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...they break.
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The design of this bridge meant the shake was more obvious.
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It bounces up and down.
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And it probably wasn't intentional(!) But clearly it wasn't dangerous, as proven
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by the fact that the bridge stood for 90 years,
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taking all the jumping around and abuse
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that local children, and adults, could throw at it.
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But nothing lasts forever.
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In 2017, an inspection looked at the corrosion and damage
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that had accumulated over the years on the bridge.
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And, well, it'd been built to last with good materials.
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But we're near the ocean here, and 90 years of salty air and shaking
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meant that the metal had corroded, and wires had broken and frayed.
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The report said, in short: the bridge had about three years
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before it had to be closed, and repairs were needed immediately.
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So it was repaired.
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Not rebuilt: the engineers reused or matched materials as far as possible.
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They took the deck of the bridge apart, fixed it up off-site, and then put it back together,
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taking care to keep the height and positioning the same.
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They replaced the suspension cables with brand new ones,
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and repaired the towers where they stood.
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And they gave the bridge a fresh coat of paint.
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But here's the problem.
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This bridge is on the local Record of Protected Structures.
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It must be maintained and repaired, but it also can't be changed.
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- There was public consultation, and of course many people actually wrote in,
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going "keep the shake, keep the shake, keep the shake, keep the shake".
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And in fairness to the engineers who worked on the project,
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I think they did achieve that.
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People have had a lot of fun
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walking across the bridge, admiring the river, jumping on it.
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Like, this has been ongoing for 90 years.
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- Before the work started, the engineers used accelerometers
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to measure how the bridge responded to someone jumping right in the middle.
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And they found that the bridge bounces up and down at about 2.3 cycles a second.
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So as part of the design process, they used computer modelling
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to work out how the new cables would behave.
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And they made sure to keep the bridge's total mass as close as possible
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to how it was before.
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Bridges shake and twist in three dimensions, of course,
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it's not just up-and-down.
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But up-and-down is the direction
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you feel the most when you're standing up there!
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And all the data showed that, in all three dimensions, the repaired
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the repaired Shakey Bridge was moving more or less as it did before.
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There was a slight change.
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But arguably that just took it
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closer to how it shook when it was brand new, nearly a century earlier.
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The bridge now goes up and down at 2.2 cycles a second.
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It would have been entirely possible, with modern technology and materials,
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to build an identical looking bridge that was much more stable.
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Normally, that's what engineers do: they try to damp down vibrations.
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But in this one case, their job was to keep things the same.
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Fixing the shake would not have been preservation.
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The goal here was to repair this bridge so that it can survive,
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and shake the residents of Cork for another century to come.