28 Jun 00
Engineers pinpoint cause of Millennium Bridge sway
A previously unrecognised phenomena has been blamed for causing the excessive swaying of London's Millennium Footbridge across the Thames, which was closed only two days after opening. According to Tony Fitzpatrick of consultant Ove Arup & Partners, the movement was caused by a combination of lateral forces from pedestrians walking in a synchronised fashion, and the horizontal movement of the bridge deck. The measured damping of the bridge is only around 1% of critical; as the random footfall of pedestrians creates horizontal movement of the deck, the pedestrians then begin to synchronise their walking motion in order to steady themselves. This synchronised motion then amplifies the horizontal motion of the deck and creates the excessive swaying motion that was seen on the opening day. Fitzpatrick told a press conference in London today that only a couple of similar cases had been recorded worldwide; in 1989 a footbridge in Japan experienced a similar problem, but the client was so embarrassed about it that engineers were forbidden from publicising the results of their investigations. The phenomena is also believed to be responsible for excessive swaying of the new Solferino Footbridge in Paris.