Revealed: why the wobbly bridge wobbled

(Getty)

The mysterious wobble of the Millennium Bridge which caused the £18.2m "blade of light" to sway dangerously was caused by the tiny foot adjustments people make to keep their balance, a scientist believes.

On its opening day on 10 June 2000, the Millennium Bridge began to wobble so violently after thousands of pedestrians tried to walk across that it had to be closed. The 320m-long suspension bridge, connecting the financial district of the City of London to Bankside in south London, had been hailed as a "pure expression of engineering structure". Until now, it was assumed that the fault was that its design had failed to take into account the tendency of pedestrians to synchronise their leg movements.

But a re-evaluation by John Macdonald, senior lecturer in civil engineering at Bristol University, found that the wobble was caused by the tiny forces on the bridge generated when each foot is adjusted during walking to keep a person's balance.

The Millennium Bridge problem was solved by fitting 91 dampers to absorb lateral and vertical oscillations. It re-opened in 2002 after the changes cost an extra £5m.