Millennium Bridge, London people walking caused small sideways oscillations in the bridge, which in turn caused people on the bridge to sway in step, increasing the amplitude of the bridge oscillations and continually reinforcing the effect. On the day of opening, the bridge was crossed by 90,000 people, with up to 2,000 on the bridge at any one time. Resonant vibrational modes due to vertical loads (such as trains, traffic, pedestrians) and wind loads are well understood in bridge design. In the case of the Millennium Bridge, because the lateral motion caused the pedestrians loading the bridge to directly participate with the bridge,
Millennium Bridge, London Millennium Commission and the London Bridge Trust. It opened on 10 June 2000 (two months late). Unexpected lateral vibration (resonant structural response) caused the bridge to be closed on 12 June 2000 for modifications. Attempts were made to limit the number of people crossing the bridge. This led to long queues but was ineffective to dampen the vibrations. Closure of the bridge only two days after opening attracted public criticism of it as another high-profile British Millennium project that suffered an embarrassing setback, akin to how many saw the Millennium Dome. Vibration was attributed to an under-researched phenomenon whereby pedestrians