Hi Ben, how are you? 

 

Hi. Yeah, very well. How are you? 

 

Yeah, very good. So, hello! I wanted to talk to you about two of your bridges - one bridge and one viaduct really - the first being your new pedestrian bridge at King's Cross. Could you talk about that in terms of its back story, because I think there's a nice detail about the actual site that the bridge spans and a previous bridge that used to do something quite relevant to the site?

 

That's right. Yeah. The new the Esperance Bridge - that's the name of the structure that has been given to it by the kids at Kings Cross Academy - is sitting on the site of a previous bridge, a previous truss actually as well, that dates from when the area was functioning as a coal drops. So, it was all railway lines associated with King's Cross and St Pancras, and there was a previous bridge, as I say, on the site. It was very much a utilitarian structure. It was for the servicing of the railways and the coal drops. And I suppose the bridge that we have designed takes something from that heritage, both in a metaphoric way, but also in a literal way. We have adopted a truss form, but we have worked into it and crafted that form in a way that is quite unusual, I think. But also literally, we are borrowing abutments from that previous bridge, so some of the structure that we are using to support our bridge, at either end, actually dates back from that first bridge. So, in a way we're recycling elements of the bridge, which is not something that as a user, you will ever really see because it's all buried away and hidden by the brickwork either side of the canal. But it's a rather nice thing for us as designers that we are recycling elements of that bridge.

 

How did the project actually come about?

 

So, the Argent master plan for Kings Cross that received consent, some time ago now, always had a bridge in that location. In the parlance of the Argent masterplan, it is KCBR2, so Kings Cross bridge two - bridge one being the bridge immediately to the east, which is the carriageway bridge. And then bridge three being around the corner connecting Coal Drops directly with Somers Town, which is a previous bridge that we did for the same client. And I think off the back of that experience on Somers Town, the client was very keen to appoint us to design and procure the new bridge. It was the same design team, and what was really wonderful for us was that it ended up being the same fabrication team as well. So, we were already very close knit, if you like, and it was just a joy bringing the team back together.

 

You've developed quite an expertise and portfolio in bridge design. What is it about bridges that you like, (presumably), and, I suppose, as a subsidiary question, where does engineering stop and architecture start with something like that?

 

I mean, that last one's a great question! But I think the attraction of bridges... I mean, I'd say that I love designing bridges, and so do my colleagues in the practice. It is a sort of a niche field for architects, I suppose. And if you're passionate about it, then it's something that you can pursue with a passion. What attracts me most about bridges is their instrumentality. Obviously, as a practice, we design buildings as well, but buildings are instrumental in lots of different ways, such that they sometimes lose purity in a way, whereas bridges have this amazing purity, because they are instrumental in terms of getting you from A to B across an obstacle. And really, that's it. You know, they don't need to worry about keeping the rain out; they don't need to worry about circulation conflicts necessarily - although there can be sometimes. They tend to be very, very pure design challenges. And those challenges are addressed through a combination of structure and form. And again, in a way that is far purer than in a building. Which is not to say that I prefer designing bridges to buildings, because I don't. I mean, it's all part of the same kind of world in a way. But there is something - it's almost like product design, in that in product design, you're generally trying to achieve a particular thing. So, it's almost like product design, writ large, if you like. That makes for a fascinating design challenge.

 

Sure. And so when it comes to a viaduct that needs to be 'nestling' in its environment in a very light touch way, which I presume is one of the necessities for your HS2 work with the Wendover Dean viaduct... I'm presuming that is part of the the design brief? And also, could you talk about that project in terms of its technological achievement, and also its carbon achievements?

 

Sure. Yeah, absolutely. I think, in the case of Wendover Dean viaduct, you have the same challenges. It's the same sort of instrumental device, if you like. It's conveying the train across a little side valley, in the Chilterns AONB in the case of that particular structure. And effectively what we're providing, or what the combined civils structural, architectural team are providing in this case, is a rigid platform that can take a high-speed railway. So, it needs to be incredibly stiff. And an order of magnitude stiffer than any other type of bridge. We tend to try and avoid wobbly bridge and dynamic excitation and what have you in any structure. But this becomes particularly acute with a high-speed rail bridge. And so, the challenge of making a structure sufficiently stiff, and yet, incorporating it into such a special landscape becomes a kind of a key aspect of the design problem. So, to make it stiff, that basically means the structure gets deeper, it gets additional material, additional depth in the spanning beams, and so forth. So, we're looking at visual ways, or techniques in terms not only of the overall composition, but also in some of the details as to how you can start to mitigate some of that depth, that additional beam depth. So, one thing very straightforwardly is we are using weathering steel. And we're setting the weathering steel beams back away from the edge of the structure. So, they're thrown into shadow. And that helps because this viaduct, in particular, will only ever really be seen backgrounded against terrain. It's only visible against the sky when you walk underneath it. Otherwise, all the public rights of way and the public highways near it, you're looking at it, you're either looking down on the structure or you're looking up at it but against the hillside. So having weathering steel helps to kind of not quite blend it., but you're recessing part of the structure and you're sort of starting to get the same kind of tonality as you have in the landscape. So, it helps to minimize its apparent depth. And then also, in detail terms, we're looking at extending the pier, up past the bottom of the beam to almost touch the parapet. So, you've got the light component of the concrete parapet and then the light component of the pier, almost touching one another. And that helps to again, push back that beam depth. They are simple things in a way but in visual terms they can be quite effective. And, like I say, it's all about trying to mitigate what needs to be an enormously stiff structure to convey these vehicles.

And apparently there's going to be 50 of these viaducts built between London and the West Midlands. Are they all of this of this general concept?

 

No, they're not. We're working for the Eiffage Kier Ferrovial Bam main works civils contractor

 

Yeah. So that's just the one viaduct?

 

No - we're designing 15 viaducts and I think it's 70 over-bridges, and some other structures as well. But we've got one other viaduct which is quite similar. It's quite close by to the Wendover Dean viaduct. And then there are a couple of further viaducts that do share some similarities again. But in fact, all of these viaducts are being designed for their contexts. Or at least in the case of our patch, if you like, which is the central section of HS2. They're being designed in a very particular way for each of their locations.

 

Obviously, with something like HS2 a lot of the furore has been about perceived damage to the environment. I noticed that you're also on the Cairngorms Trust, and I wondered if that sensibility that you have has been useful in terms of light touch, and the beauty of the landscape, and appreciation thereof?

 

Certainly, it is very important to me personally. But I probably wouldn't say that I feel it any more than anyone else. But it's certainly very important to me and to us as a practice. And I think that, you know, there's a lot of - how can I put it politely? There's a lot of misinformation about the project... 

 

Yeah

 

...In the public domain. And, I mean, there are certain quite eye-catching statistics, if you like, that you can, we can reel off. For instance, the well-known one, which is that the embodied carbon of the construction of phase one, and its operation for 120 years, is less than the carbon emissions of one month of UK road transport. 

 

Amazing!

 

Which is an astonishing thing. And, I mean, in the case of Wendover Dean Viaduct the collective team had an obligation in the contract to reduce the embodied carbon in the structure by I think it's circa 50%, relative to a conventional box girder type viaduct, which is by far the most common type for this sort of application. And we've already achieved that. And in fact, the structural engineers that we're working with are on track to further better that achievement. I mean, in the grand scheme of things, the embodied carbon of this one single viaduct is relatively small compared to the entire line. But that also makes it very, very small compared to, for instance, the sort of emissions that you might encounter on one single day of road transport in the UK. And because the purpose of this project is to at least enable a policy shift in favour of low carbon transport, then, you know, I think it's all pushing in the right direction.

 

Yeah. Because it struggled with its PR, right from the start, didn't it, HS2? Because, you know, the notion of it shaving 30 minutes off a journey to Birmingham, 'blah, blah', was not really the message. And yet it was pumped around.

 

Correct. That's a very good point. I mean, the point is, I suppose, that it achieves various things. And so, it's a question of messaging. It is also a question of what is the priority for a given audience at a particular point in time? And ultimately, it is about providing an enormous upgrade to the existing railway, particularly in the southern half of the UK. And the fact that you're going to do this, you might as well, in fact, you ought to, make it a high speed rail line in order to achieve that, rather than conventional rail.  Because high speed rail brings just so much more capacity again.

 

Yeah. Well, congratulations. It looks good. And I can't wait to go on a train at, what is it? 150 miles an hour? 125 miles an hour?

 

I think we're designing for 400 kilometres per hour. 

 

Oh really?

 

The design speed is very high. But again, that's about being responsible to the future and providing flexibility and durability. I mean, that viaduct has been designed for 120 years to major maintenance, which is essentially permanent, you know? Again, it's a different order of technical challenge to normal bridging structures. 

 

Well, we talked about tiny to massive scale here, didn't we? The tale of two bridges in a way. So, thank you very much for your time. It's really fascinating. 

 

No problem. I just remembered that I didn't answer one of your questions!

 

 No! Engineering-ness?

 

Yes. Engineering versus architecture! 

 

Go on.

 

Well, I mean, the thing I would say is that, in our experience, and this is something that I first encountered when I was very young, working at Wilkinson Eyre architects but have done ever since, is that the best bridges are pure collaboration between architect and then engineer. To the point where, yes, although, the engineer has his or her responsibilities in his or her appointment, and we have our responsibilities in our appointment and you can draw lines between the two, in fact, the design process of the best bridges is pure collaboration. In that, you know, hand on heart, I can't really say what bit of the Esperance Bridge in Kings Cross we authored, versus what bit Arup authored. You know, we're all sitting around that table. And the fact that we might be architects and they might be structural engineers is basically irrelevant in terms of the design conversation. That's not always the case. But it's always the case with a good bridge!

 

Brilliant. Thank you very much for your time. That was really fascinating. 

 

No problem! Thank you very much indeed as well. Thanks David. Bye.