London

Think Millennium Bridge, and everybody thinks London. Of course, everybody has heard about the ill-starred London Millennium Bridge, for all the wrong reasons. In my opinion, it is the most elegant and graceful of all the Millennium bridges in the country (although Lancaster runs a close second). Technically a suspension bridge, the design is unique, with the suspension cables only making a small angle with the horizontal. This design makes for a slim and uncluttered appearance, whilst from the bridge the views of the river up- and down-stream are unobstructed. 

The setting of the bridge is superb. Like the Gateshead bridge with the Baltic, the London bridge has a modern art gallery - the Tate Modern at its southern end. To the north, the bridge lines up with the dome of St Paul's. 

After a royal "inauguration" on 9 May, 2000, the bridge was "opened" to the public on 10 June but closed two days later.

What was all the fuss about? The  large number of people swarming onto the bridge set up an alarming sideways oscillation of up to 70 mm amplitude. The result - the bridge was closed two days after opening and remained closed for more than 20 months whilst the nature of the problem was identified and the solution was sought.  Laboratory tests proved inconclusive, so Ove Arup had to deploy large numbers of their own employees as guinea pigs to test the bridge in "live" conditions. The unique design led to the discovery of a previously unsuspected and unreported problem. Large numbers of people on the bridge tended to sway sideways in unison to compensate for the small natural sideways movement of the bridge. This "locked in" to the natural frequency of the bridge leading to an unacceptable amount of lateral movement. The solution finally adopted was to fit dampers under the deck of the bridge, with minimal visual impact on the graceful lines of the bridge. The bridge was eventually re-opened on February 22, 2002. An expensive and worrying time for the contractors - but as they say there is no gain without pain, and no progress without bold design and the occassional hiccup.

For the full story, the Ove Arup website gives an excellent account with no holds barred complete with video clips. A more succinct technical account can be found in the Architecture Week article. The Photoguide to London provides a good picture gallery.

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But the Millennium Bridge is not the only noteworthy footbridge across the Thames. The Jubilee footbridges which flank either side of the Hungerford Rail Bridge are well worth a visit. Walkways were constructed on both the downstream and the upstream side of the rail bridge when it was constructed in 1864, although the upstream one was subsequently demolished to make way for the widening of the railway. The old footbridge was narrow, dilapidated and dangerous, so a decision was made to replace it shortly into the new millennium.

Footbridges on both sides of the rail bridge were constructed. The design is complex;  inclined pylons rise from the foundations of the rail bridge  which were enclosed in concrete as a precaution against damage by collision from river craft. The deck is supported both by deck stays from the pylons and by back stays to the rail bridge. The bridges are both 300 metres long and 4 metres wide, and accessed at each end by steps.

The bridges were opened in 2002, the year of the Queen's Golden Jubilee. The bridges have received awards both from the Royal Fine Art Commission and the Institution of Structural Engineers.

A further footbridge, linking Battersea and Chelsea has been granted approval and will commemorate the Queen's Diamond Jubilee, albeit a little late.

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The Paddington Basin is the continuation of the Paddington Arm of the Grand Union Canal which runs for a little over one kilometre from Little Venice to a blind end. At Little Venice, a connection is made with the Regent's Canal which runs eastwards to the Thames estuary at Limehouse Basin, and which also connects to the Hertford Union Canal and on to the River Lee Navigation.

The short length of the Paddington Basin is the site of three interesting footbridges - known as the Harrow Road, Fan (Merchant Square) and  Rolling footbridges. 

The Harrow Road footbridge is located just south-east of the canal junction at Little Venice, ingeniously inserted into a restricted space in the shadow of the Westway Viaduct.

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The Fan Bridge is a spectacular footbridge spanning the head of the Paddington Basin and was opened in September 2014. 3 metres wide and 20 metres long, it comprises five segments which rise individually to provide clearance for boats to pass - notwithstanding that passing boats are as rare as hen's teeth. Named the "Fan" bridge for its likeness to the action of a Japanese hand fan. Unfortunately I have not been able to witness at first hand the operation of either this or the Rolling Bridge nearby.  An action-packed video shows the operation of both bridges which is timetabled for 12 noon on Wednesdays and Fridays and at 2 pm on Saturdays. See also this link. Both bridges would appear to be  exercises in engineering ingenuity rather than practical solutions to real problems.

The Fan Bridge replaced another interesting, retractable bridge, the Helix Bridge. See link for technical details.

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 It may not be much to look at, but the Rolling Bridge built in 2004 over a small arm off the Paddington Basin is another truly amazing piece of mechanical ingenuity - the only one of its type in the world. The term "curling" rather than "rolling" might be a more accurate description as it is designed to curl up like an armadillo. See here for pictures of the bridge in semi-rolled and fully-rolled mode.

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