28 November 2013

Durham Bridges: 1. Kingsgate Bridge

The last few posts dealt with bridges on Teesside that I visited as part of an IABSE study tour. On the afternoon of the first day, we travelled a little further north, to Durham. Our first stop: Kingsgate Bridge.

Built in 1963, this footbridge was personally designed by Ove Arup, and is reported to have been one of his favourite designs. At the time, Arup was probably more involved in running his Partnership than in the specifics of individual projects, but for the Kingsgate Bridge he immersed himself in every detail.

Famously, the University in Durham had only £35,000 to spend on a new bridge linking their older buildings by Durham Cathedral to a new site on the opposite bank of the River Wear. They anticipated this would be enough only for a bridge at the river valley floor, some 17m below the tops of the valley slopes. Arup convinced them that the same money could pay for a 107m long bridge running at height, if the structure could be made efficient.

The engineering of the bridge displays a masterful balance of structural requirements with construction requirements. The bridge has only two main support points, each on a piled base. From these, V-shaped "fingers" carry the bridge deck, reducing the deck spans. The arrangement also allowed for a highly economic method of construction, eliminating the need to construct reinforced concrete in-situ above the river. Each half of the bridge was built parallel to its river bank. The pier supports conceal an internal cone, which allowed both 150-ton halves of the bridge to be rotated 90 degrees into their final position.

This is certainly not a unique construction method, but it is relatively rare and I'm not sure whether there were any precursors in the UK at this time.

At first sight, the bridge is not an immediately loveable design, notwithstanding its status as a Grade I Listed Building. The supports are stiff and angular, and the bridge deck, apparently envisaged as a "thin, taut, white band stretching horizontally across the valley", is blank and lumpen. As the river banks have become considerably overgrown, it's also almost impossible to see the entire bridge as the single composition which was originally built.

Even in detail, the bridge has its flaws, and I find the "fingertips" which connect the finger piers to the deck to be particularly awkward. There's little sense of how the forces are transmitted (the deck is in tension between the fingers, and that considerable force has to be transmitted through these tiny fingertips). There's no shaping of the concrete to respond to those forces either: the band-like concrete side-beams are the same depth at the ends as at the middle, although the stresses in each section are very different. Arup was certainly not a master of concrete on the level of Maillart, Torroja, Candela or their ilk.

Nonetheless, it's an admirable bridge in many ways. The detailing of the finger piers is interesting, minimising material while providing stiffness by means of a folded cross-section that constantly transforms from top to bottom. And the bronze expansion joints where the two bridge halves connect are quite exquisite. These allow horizontal movement while locking the bridge decks together vertically.

I am not generally a fan of "half-through" footbridges, where solid beams on either side of the walkway double as the parapets. Generally, visual transparency seems preferable. However, for a footbridge at height, as is the case here, solid parapets do offer a much greater sense of security for the bridge users.

Shortly after the bridge was built, Concrete Quarterly praised it for having a "subtlety without chi-chi or softness, but keeping in its fineness a certain strength of plane". Its angularity closely recalls the great Italian engineer Riccardo Morandi, whose structures are equally hard to love. Today, I think it would be improved considerably simply by cutting down a few trees and giving it the chance to be seen properly as a sculptural object within the landscape.

Further information


Bridge Ink said...

80Interesting comparison with the works of Morandi (whose works I find very easy to love). Morandi's Paul Sauer Bridge in South Africa was also constructed on opposite sides and rotated into connection.

The Happy Pontist said...

The Paul Sauer bridge is one of Morandi's better works, for sure. Of course, the rotation was different for that bridge, vertical rather than horizontal, and it was a technique Morandi had already used in 1955 for the Lussia Bridge.

There's a list of bridges swung horizontally into place at Structurae (http://en.structurae.de/structures/mtype/index.cfm?id=3022) although it's far from complete. Troyano claims Kingsgate to be the first bridge built by this technique.

Richard Cooke said...

A supplementary comment on the expansion joint which works so well visually and functionally. Sir Ove apparently took great satisfaction from the geometry as the interlocking 'T' and 'U' symbolised the connection between the Town and the University. It is not known if he actually realised this until after the bridge was completed!

BTW Your blog is excellent and always hits the right note. I look forward to more...

The Happy Pontist said...

Thanks Richard!

David Toll said...

The Institution of Civil Engineers, Arup, Durham University and Durham County Council will be celebrating the 50th Anniversary of the opening of Kingsgate Bridge on 11th December 2013. If anyone would like to joint the event, do email d.g.tolldurham.ac.uk.

Rod Shaw said...

My Dad, Civil Engineer Frank Shaw surveyed potential sites for the location of this bridge. Using a state-of-the-art diamond cutter he drilled several boreholes along the banks to determine the best position. One of the excavated samples was later polished and made into a paperweight for Ove Arup.