On this day – June 10th

The Wobbly Bridge opens – and closes

The Millennium Bridge officially opened by the Queen on 10th June 2000, two months later than originally planned. Two days later, on 12 June 2000, it was closed again. It then reopened – this time for good – on 27 February 2002.

Its official title is the London Millennium Footbridge. But no-one calls it that. Instead, it'll probably always be called the Wobbly Bridge.

Built using 'lateral suspension', an engineering innovation allowing suspension bridges to be built without tall supporting columns, the Thames' newest crossing was hit by a phenomenon called Synchronous Lateral Excitation when loads of people flooded over its shiny new deck.

Around 80,000 people crossed the bridge on its opening day, with around 2,000 on the bridge at any one time.

Those on the southern and central spans felt the bridge begin to sway and twist in regular oscillations. Feeling unsteady, the pedestrians altered their gait to the same lateral rhythm as the bridge. The adjusted footsteps just magnified the motion: the more it happened, the more people responded to the movement; and the worse it got.

While there was no chance that the bridge actually would fall down, engineers felt that the wobble needed to be stopped. In the end, the problem was fixed with two different types of damper: viscous dampers (like car shock absorbers); and tuned mass dampers: a large mass stiffened by springs, sometimes used in buildings in earthquake zones.

The Millennium Bridge is far from being London's first wobbly bridge: the 1873 Albert Bridge is nicknamed the Trembling Lady, with a notice that troops must 'break step' when crossing to prevent these vibrations from becoming too pronounced.

And how much did it cost to build the Wobbly Bridge?

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