24 April 2016

Yorkshire Bridges: 8. Weathering steel footbridge at University of York

I visited the University of York a while back. The main campus is built around an artificial lake which is crossed by a number of footbridges.

The weathering steel footbridge is not just any footbridge in weathering steel: it is claimed to be the first weathering steel bridge ever built in the UK, dating from 1967. With nearly half a century of weathering having taken place since construction, I thought this would be an interesting bridge to visit to see how the weathering steel patina can develop in the long-term.

As it turns out, the patina is probably the bridge's least interesting attribute. It's an attractive dark brown, which looks like it has stabilised well. There's no sign of ongoing corrosion anywhere, indicating that the bridge was well detailed, and no evidence of graffiti or other vandalism. The bridge drains freely into the lake via a series of scuppers along each edge.

The bridge's main interest is in its shape. It is wonderfully slender in elevation, broadly taking a three-pinned "arch" form which is vaguely reminiscent of Robert Maillart's Tavanasa Footbridge.

The deck consists of two steel box girders, each triangular in elevation. They are deepest at their points of support, which consist of slender steel box struts carrying the loads back to the abutments at a very shallow angle.

All this looks quite delightful in elevation, but is just plain odd when viewed at closer hand. The struts are much narrower than the deck girders, so it's apparent that there must be significant internal diaphragms within the boxes to transfer loads between the main structural elements. I'm struggling to see the rationale, either architectural or structural, for doing this, as the forces just don't seem to "flow" down to the ground.

Nonetheless, this is an attractive bridge, which has survived well, and clearly demonstrates both the longevity of weathering steel, and its ability to sit attractively within semi-rural surroundings.

There are some other interesting footbridges at the same site, I'll post details when I get a chance.

No comments: