Speaker A
Hi, I'm Paul Kassabian, I'm a structural engineer.
Paul Kassabian, a structural engineer, details the design, fabrication, and erection of the 1,200-ton Gateshead Millennium Bridge, highlighting its unique arch and cable-stayed structure.
Key Takeaways
- Innovative design combining arch compression and cable-stayed torsion.
- Building the entire bridge on land enabled precise fabrication and minimized river disruption.
- Use of a large floating crane allowed efficient single-day placement.
- Temporary structural measures are crucial to manage forces during assembly.
- The project exemplifies complex engineering collaboration and advanced fabrication techniques.
Summary
- The Gateshead Millennium Bridge is a 1,200-ton cable-stayed arch bridge spanning the River Tyne.
- The bridge features a parabolic arch in compression and a curved deck connected by cables on one side, causing torsion in the arch.
- The arch and deck are constructed as stiffened box girders with perimeter plates and internal stiffeners for strength and torsion resistance.
- The entire bridge was fabricated on land to allow precise assembly and minimize river closure time during installation.
- A large inshore floating crane was used to lift and place the entire bridge in one day over the active River Tyne.
- Temporary supports and hydraulic rams were employed to rotate and position the bridge accurately.
- Tied arch principles were used temporarily on land to counteract the outward thrust of the arch during assembly.
- The project was a significant part of Paul Kassabian’s career, involving detailed steel fabrication and erection work.
- The video includes detailed images and explanations of the bridge’s design, fabrication, and erection process.
- The bridge’s innovative design and construction techniques highlight advancements in structural engineering.
Full Transcript — Download SRT & Markdown
Speaker A
And the Gateshead Millennium Bridge was carried upriver by what at the time was the world's largest inshore floating crane.
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It was a 1200 ton bridge and it was placed in one day.
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I was lucky enough to work at the steel fabrication and erection firm for that project for the whole year before that single day, only on this project.
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This video I want to share an introduction to what the Gateshead Millennium Bridge was as a design, which was spectacular in its own right, and also a lot of detail and images and video on the bridge fabrication and erection.
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It is truly an amazing project, I'm honored to have been part of it.
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It was a really fundamental part of my career and I hope you enjoy this.
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So here's the design competition winning image of the Gateshead Millennium Bridge.
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A nighttime shot because back in the 90s that's what a lot of the images were.
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You'll immediately see the arch bridge coming across and spanning while also having this complementary curved deck.
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And the cables that are going straight from the arch to the deck, so this is a cable stayed bridge.
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Are going from one side of the arch and going to one side of the deck.
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So there's a lot going on here.
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Also along the bottom you'll see some images of how the bridge rotates such that it can open.
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And I'll show you a couple more images about that later.
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So let's talk a bit about what's going on with the arch.
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So as I've used as a diagram in my previous arch video.
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We have the arch in compression.
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It's generally a parabolic shape such that it can be sort of minimal section as possible.
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And importantly, arches thrust outward.
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Right?
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You'll see that with the hands that I've got shown here.
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So not only is the arch being held up, it's also being held in at the ends.
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To prevent it pushing outwards.
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And prevent it splaying out.
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It always pushes out.
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And another thing that's going on because the cables are going to one side.
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The arch is also in torsion.
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And so here is a section of the arch.
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You're going to see plate around the perimeter.
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And stiffening as well.
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And so there's this is essentially acting like a tube.
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Remember I did a video on torsion and tubes.
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Tubes are really good at carrying torsion because the material is consistent all the way around the centroid.
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And it doesn't have to be circular, it can be any shape as long as you've got material going all the way around.
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And so here's what you're seeing from that previous drawing of the material plate around the perimeter.
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These are different sections of the arch being welded together.
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Also there's stiffeners that are are stabilizing that perimeter plate.
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This is a stiffened box girder is the phrase that's used.
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The same thing happens for the deck.
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This is the hollow tubular in form section.
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So perimeter plate.
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The this is where people walk and the bicycles go on this cantilevered area.
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And the cable comes in from the inside of the curve.
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I know this looks empty.
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But here's a photograph of the deck being fabricated.
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It's actually upside down here because this part is flat.
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So you'll see stiffeners running in both directions along the plate and then also these sort of cross girder stiffeners as well.
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And if we do a close-up of where the cable comes in.
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And look at the inside of this deck.
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You'll see there's a whole set of the stiffeners are sort of placed diagonally to carry the force localized from the cable that comes in from the outside.
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Will be inside this stiffened cylinder and bear on this stiffened plate from the underside.
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And you'll see an image of them stressing the cables later as well.
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So here's the top piece of nine forming the arch.
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This 27 tons.
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That's just this piece.
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The whole arch weighs 350 tons.
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The whole bridge weighed 1200 tons.
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And here's a lug that you'll be used later on to pick up the whole arch.
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And so we're placing this bridge over the River Tyne.
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This is Gateshead over here.
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So the Gateshead Millennium Bridge.
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And one of the issues that comes up when you're especially when you're dealing with an arched bridge.
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Which is a situation where the arch only works when the arch is complete.
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Right?
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And how do you place something like that over a river?
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Especially when the river is an active river.
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This is the River Tyne.
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This isn't something that we could close for weeks or months on end.
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So a big problem was solving the issue of how to build this and place it.
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And luckily we found further to the east, which is the background of this photograph, a large layout area of land.
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And our plan, quite a bold plan, was to build the entire bridge, not just the arch or just the deck.
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The entire bridge on land.
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Pick it up as one and then place it.
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The advantage of being we can control this assembly and fabrication outside and take the time we need to get it right.
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And then we've also minimized the amount of time that the active river has to be closed while we're placing the bridge.
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So here's the arch being placed together and the and the bridge deck in its sections.
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And we rotated the arch upwards, it's rotated about these bearings at the end.
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And placed it temporarily on this column support.
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Remember with columns, you want to have area away from the middle.
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Um it's open lattice framework so that it's stabilizing itself as well.
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And remember this green square sectioned trussed object.
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We'll see it again later.
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So we placed it temporarily on this support.
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Because the cables are just hanging.
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We used this bearing that is going to get placed at the ends of the arch.
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I just you can see it in place here.
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And I wanted to explain that this goes at the bottom of each end of the arch.
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And that's what when it goes to site, that's what it's pushed on by three hydraulic rams at either end.
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And they are the ones that rotate the whole bridge up.
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And when it comes back down, it actually rests the deck rests in its stable.
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By being supported on this bearing point and on a front bearing point as well.
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So there's four points of support when it normally is in its normal down position.
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And so here, remember we saw the inside of the deck.
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When the cables are coming through.
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We've got the sagging cable because it's sagging under its own weight.
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While they are tensioning up the cable to the deck.
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Remember the diagram I used in my cable video.
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Um where whether whether you've got actual weights hung from a cable or it's just the cable's self weight itself.
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It will always drape to some extent.
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As you pull on the cable, it gets more and more straight.
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It will never actually be straight given gravity and its own weight.
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But it may look quite straight to the eye.
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So here's the bridge in its essentially completed condition.
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Sitting on land.
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So this let us build all of this.
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Uh in in an easy way of accessibility.
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You can see the cables.
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They're a little hard to see but they're going diagonally here.
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And notice if you recognize this is that big green trust part that we've added some ends on.
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And that's going to be the lifting beam to help us when we support from the big crane to a single point.
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And the cables from the crane are going to come down to either end and pick up this bridge.
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And so we need a lifting beam that's in compression.
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So that we can keep the cables splayed outward.
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Right?
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So we've got a double use out of that piece of temporary works.
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And at one end of the bridge, just to give you a sense of scale, that's a person.
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I mean, he's he's crouched down, but still.
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That's a whole normal human being.
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And because we're on land and we've lifted the bridge and it's in its final state.
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Do you remember I mentioned arches always want to push out?
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Well, we didn't have the ability to build something to push back on that on land.
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But we were on land.
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So what we did was we tied each end of the arch back to itself.
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That's what this cable is doing as a piece of temporary equipment.
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If you remember tied arches are a way of connecting the bottom of each end of the arch to itself.
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And instead of pushing in, all you need to do is hold it up.
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Now it's sort of in a self state of equilibrium, which is very beneficial if you're trying to pick something up.
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And this is how we picked it up.
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Here's the diagram of the crane.
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The very modestly titled Asian Hercules 2.
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And we're picking it up.
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This is the single point that it's going to be picked up from because the bridge will have to be rotated.
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You'll see that so it can fit up the river.
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And then that's coming down to that square section that I showed you.
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The green, the green long lifting beam.
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Down to these points.
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And you'll also see a a connection down here to the front, which I'll explain in in a second here.
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So we did a lot of analysis in picking up this bridge.
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I know what you're seeing.
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This is after we did all analysis.
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But you know what, it's a really good idea to test out your plan for all of your stages of a pickup sequence and a landing sequence.
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That you're not missing anything.
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So to represent it with some very basic models.
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This is my ruler.
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A bolt all hooked together to sort of represent hanging this bridge from a single point.
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Okay, that doesn't seem particularly complicated.
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But the reality is is that when we land the back of this bridge, this cable will go slack.
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And this cable wasn't just lifting up this end, it was also being balanced by this cable.
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Which is inclined and carrying less weight.
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Just the deck.
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And so if we land this bottom part only and this cable goes slack, well then nothing's balancing the horizontal part of this cable.
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Right?
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So the whole thing would want to kick back.
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And you can do that with this little model and it's no big deal.
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Little ruler and a bolt backs away.
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Well, you imagine a 1200 ton bridge being lowered and then backing up into a whole bunch of people on site.
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That would be disastrous.
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So we planned to have this additional pickup point at the front just to be used for the landing.
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So that we could stabilize it.
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And here we represent the landing on.
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Um so for some of you, this is what's called a camera film roll.
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Where you took 24 photos.
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That's what you got.
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24 or 36 if you really splurged and bought more.
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Um so this is our landing and stabilizing it on the front.
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So here we're ready on the pickup day.
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There's the actual crane.
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Coming into position, slack cables that are about to be taken up the load in tension.
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And then balance off their horizontal component in compression in this lifting beam.
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And here we do here we are coming up the river.
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Um really fun story.
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The harbormaster controls the River Tyne.
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And we very much needed him on our side because we were closing down the river for a bit.
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And we needed to have various negotiations with him.
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So we had the good idea of asking him, hey, when this really impressive bridge and crane come up river.
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Would you like to lead it in so that everyone sees you?
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And he was very chuffed by this.
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Um so we kind of won him over um for that.
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And so here he is.
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That's him.
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That's the harbormaster.
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So coming in, bringing leading forward and for everyone to see um the bridge.
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So it's turned uh lengthwise on so that it could fit up this winding river.
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Um there's the green lifting uh spurder beam.
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And it's all hung from this single point.
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This is the last photograph I took for myself on on the Gateshead side.
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Before I got into a little boat and went over to the Newcastle side, which is the side I was controlling.
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Um so it's quite an intimidating sight to see.
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Um so now we're going to move to a few images.
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These are by Graham Peacock taken from a helicopter.
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Um so here it here it is arriving, this is Gateshead here on the left, the south side.
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This is the Baltic Flower Mills that became a modern art museum.
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Over here on the right, the north side of the River Tyne is Newcastle.
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Um so harbormaster's doubling back.
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And he's going to help rotate the bridge.
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Here it is rotating around into position.
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And now it's lined up.
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And this is a glorious photograph because you can see how the bridge is now joining.
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A series of other bridges that cross over the River Tyne.
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Notice all of them are high.
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So um tall boats come through, but uh there's a height limit as they as they come up the river.
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Um so here it is coming into position.
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Uh another photograph of this.
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Um I think I'm either one of these people in yellow jacket or somewhere over here at this time.
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Something that I hadn't really thought through and none of us, the Newcastle side was um far busier.
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Than because this was a public area and the Gateshead side.
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This was a whole construction site.
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So while I was over here, it was quite interesting when we got there in early morning.
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Everyone's like, this is amazing.
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You guys are great.
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I was like, oh, thank you.
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And then two hours later, you know, same people are, are you still here?
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And I was like, you know, this this is difficult.
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Okay.
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Give us a moment.
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Um so here we are in position.
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Glorious photograph.
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As I said, it rotated.
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Um and uh you can see various videos of this online.
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Uh if you want to search up for it.
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And uh here it is in position while there's lots of people who can be on it.
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And then when it rotates, it takes a few minutes, obviously.
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But it rotates and comes into position here.
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It's a really clever design solution actually.
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Because as I said, you saw the higher bridges.
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So there is actually a height limit for the tall ships.
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And this is a really interesting way of moving the bridge out so it doesn't have to open up or move out of the way.
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So a really clever rotating idea by using two curved forms as an arch and a deck.
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Um I like this image because it looks like the people who were on it just got thrown off it.
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And uh it's got beautiful lighting design.
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Uh by Spears and Major.
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And uh that really adds.
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And a great photograph that shows it in context, you know, very much a design and construction project.
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Um of its day, very contemporary, you know, using our our sort of current technology.
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And representative of what we're trying to achieve, joining the history of other impressive bridge design and construction projects from the past.
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Um if you want more details on this.
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Um we wrote a paper.
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Uh I'll put a link to it in the description below.
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This is really an amazing project.
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Um and I hope you enjoyed hearing about it and learning some things about it too.
Topics:Gateshead Millennium Bridgestructural engineeringarch bridgecable-stayed bridgesteel fabricationbridge erectionfloating craneRiver Tynebridge constructionengineering design
