Bevis+-+The+Millennium+Bridge

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=__**THE MILLENNIUM BRIDGE**__= The Millennium Bridge is a 320-meter-long lateral suspension bridge connecting London's financial district to Bankside. It opened on June 10th 2000 and cost £18.2m to construct.

What happened:[[image:http://www.sciencedaily.com/images/2005/11/051103080801.jpg align="right" caption="LOOK! ITS SO BENDY!"]]
On the opening day of the Millennium Bridge, small sideways oscillations were caused in the bridge by the swaying motion of approximately 2000 pedestrians walking on it. This then caused the pedestrians to sway even more, causing the amplitude to increase. Amplitude is the magnitude of change in the oscillating variable in an oscillating system.

The problem:
Even though the walking patten of a large group of pedestrians is usually random, if a few of them accidentally synchronise, the bridge will become unstable. If the amount of synchronised pedestrians increases, the oscillations and wobbling will become stronger and can cause even more pedestrians to move in sync. Engineers tested the bridge and found that only 160 people out of the potential 2000 on the bridge needed to walk in sync to cause the problem.

Solution:
Engineers tackled the problem by adding 37 fluid-viscous dampers to control any horizontal movement and 52 tuned mass dampers for vertical movement. Damping reduces the amplitude of oscillations in a system, so in this case the oscillations of the bridge were greatly reduced. After spending another £5m, the bridge successfully reopened on February 22nd 2002 and has not had any problems since.

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Bibliography: Cornell University. "Explaining Why The Millennium Bridge Wobbled." __ScienceDaily__ 3 November 2005. 25 February 2010 .