21 March 2010

Manchester Bridges: 10. Lowry Millennium Bridge


From Manchester city centre, I went west, to Salford Quays, to see several bridges.

This first one is a vertical lift footbridge. I've seen "Lowry Centre Footbridge", the "Lowry Bridge", "Salford Quays Millennium Footbridge", "Salford Quays lift bridge", and several similar variants on its name.

It spans the Manchester Ship Canal, linking regeneration centrepieces such as the Lowry Centre to the north, and the Imperial War Museum to the south.

It was built in 1999 by Christiani & Neilsen (the steelwork was fabricated by Fairport Steelwork and Lengthline Ltd). The main designer was Mouchel Parkman, but the superstructure at least was designed by the Spanish firm of Carlos Fernandez Casado, with the mechanical and electrical systems designed by Bennett Associates (now part of Atkins).

The main span is a steel bowstring arch, 96m long (spanning 91m between its bearings) and 11m tall. The arch rib and tie are both upside-down U-shaped girders, 600mm wide by 800mm deep, and steel hanger rods connect the two. The arch tie girders carry the orthotropic steel deck (pictured left from below). The bridge parapets are in the form of glass wind deflectors, with pedestrian lighting concealed in the handrails.

The bridge deck is suspended from four towers, each 31m tall, which support the lifting sheaves and counterweights, and the entire bridge can lift approximately 18m in 3 minutes, when required. The towers are tubular steel space frames, curved for enhanced stability against wind load at the base. While nicely shaped, they'd look better with less bracing, and I wonder whether emphasising the size of the maintenance platforms at the top was a good idea.

A visually attractive lifting bridge is a rare thing indeed; I certainly can't think of any good examples in the UK, and most of the lifting bridges in the US have a very heavy, industrial appearance. It's a type of moveable bridge generally limited to longer spans, with bascules and swing bridges being more economic and maintainable for short bridges, although there are some very large swing bridges around (most notably at El Ferdan in Egypt).

At Salford Quays, I presume there was a desire not to have a support pivot in the waterway, which would restrict its width (although the new Media City footbridge being built a short distance away will be swing bridge). So a lifting bridge makes sense as a choice, even though it doesn't look like it actually opens very often.

The wind screen parapets look a bit odd to me, their height makes the deck feel quite enclosed, and while they may be effective at shielding the worst effects of the wind, you are exposed again as soon as you step off the bridge.

But on the whole, it's a reasonably attractive bridge, well detailed and kept simple so that the arch form can provide the main visual focus.

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