15 January 2012

Peter's Bridge, Norwich

I always prefer to visit a bridge before covering it here, but I have no plans to go anywhere near Norwich soon, and this bridge looked worth featuring.

It opened to the public last month, and spans the River Wensum in Norwich city centre. Spanning about 30m, it is 80m long in total, shaped like the letter "J" in plan. Designed by Ramboll, it is named for Peter Jarrold, who first came up with the idea for a bridge at this site twenty years ago.

The bridge's form is unusual - there are plenty of bridges with curved decks like this, but very few with so little obvious means of support. Most are suspended from arches, or masts, or less frequently held up by larger girders or trusses.

Peter's Bridge is built primarily in weathering steel, with a torsionally stiff box girder on the inner edge of the curve, supporting braced steel ribs. The deck has a wedge-shaped cross-section, emphasising the outer edge and making it look thinner than it really is. The deck cross-section of York Millennium Bridge has several similarities. The photos are unclear, but there appear to be a small number of very slender supports below the main edge girder.

The parapets are a combination of weathering steel uprights with stainless steel handrails and, on the outer face, mesh infill. It's a combination of materials that can be very attractive, as I've illustrated here before. However, it's also prone to vandalism and to the risk of rapid corrosion due to trapped water, particularly in the British climate.

Here, timber panels are used to prevent direct contact with the rusty inner face of the support girder, although I would not be surprised to see graffiti on the outer face of the girder in the future - this is difficult to clean off without creating a patchy finish. The deck is also timber-planking, with gaps allowing rainwater to drain straight through, and it will be interesting to see how well that performs or whether trapped moisture affects the support ribs over time.

Quibbles aside, the overall appearance is daring without unnecessary flamboyance, and it looks like a fine new structure, nicely detailed.

All photos are courtesy of mira66 on flickr. You can also see online images of the bridge under construction.

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