Editing Millennium Bridge, London (section)

===Mitigation===
Engineers at [[Arup Group|Arup]], the company that designed the bridge, conducted research into the unexpected oscillation, which they called 'synchronous lateral excitation'. The first laboratory studies used pedestrians on moving platforms at the [[University of Southampton]] and [[Imperial College London]]. Later in 2000, one span of the bridge was instrumented and tested with crowds of up to 275 people.<ref name=":0"/>

They concluded that making the bridge stiffer, to move its resonant frequency out of the excitation range, was not feasible as it would greatly change its appearance.<ref name=":0"/> Instead, the resonance was controlled by retrofitting 37 viscous fluid [[Dashpot|dampers]] to dissipate energy. These include 17 chevron dampers – long V-shaped braces under the deck panels – to control lateral movement, 4 vertical to ground dampers to control lateral and vertical movements, and 16 pier dampers to control lateral and torsional movements.<ref>{{cite book|last=Taylor|first=Douglas P.|title=Damper Retrofit of the London Millennium Footbridge - A Case Study in Biodynamic Design|url=https://www.taylordevices.com/custom/pdf/tech-papers/66-DamperRetrofit-London.pdf|publisher=Taylor Devices, Inc.|access-date=14 March 2019}}</ref><ref>{{cite book|last=Klembczyk|first=Alan R.|title=A Study in the Long-Term Performance of Specialized Low Friction Hermetically Sealed Fluid Viscous Dampers Under Nearly Continuous Operation on a Pedestrian Bridge|publisher=Taylor Devices, Inc.|url=http://www.teratec.ca/wp-content/uploads/Millennium-Bridge-Dampers-long-term-study-2.pdf|access-date=14 March 2019}}</ref> Additionally, 52 [[tuned mass damper]]s add inertia to control vertical movement. The work took from May 2001 to January 2002 and cost £5 million. After a period of testing, the bridge was reopened on 22 February 2002 and, since that date, has not been subject to significant vibration. In spite of the successful cure, the "wobbly bridge" (sometimes "wibbly-wobbly"<ref>''E.g.'', "[https://www.youtube.com/watch?v=y2FaOJxWqLE The Wibbly Wobbly Millennium Bridge in London]", YouTube; accessed 20 August 2021</ref>) epithet remains in common usage among Londoners.<ref>{{cite web|url=http://www.urban75.org/london/millennium.html|title=Millennium Bridge over the River Thames, joining the Tate Modern and St Paul's London – photos, history and background|publisher=Urban75.org|access-date=26 March 2013}}</ref><ref>{{cite web|last=Lydall|first=Ross|url=http://www.thisislondon.co.uk/standard/article-23761203-second-wobbly-bridge-for-london.do|title=Second wobbly bridge for London|publisher=[[Evening Standard]]|date=27 October 2009|access-date=26 March 2013|url-status=dead|archive-url=https://web.archive.org/web/20091030004102/http://www.thisislondon.co.uk/standard/article-23761203-second-wobbly-bridge-for-london.do|archive-date=30 October 2009}}</ref>
<gallery mode="packed" caption="Dampers">
File:Millennium Bridge decking underside.jpg|Chevron dampers
File:Bridge vert mode shock.jpg|Vertical to ground dampers
File:Bridge_horiz_mode_shock.jpg|Pier dampers
File:Moving End of Pier Damper of Millennium Bridge, London.jpg|Moving end of pier damper
File:London Millennium Bridge - Damper beneath deck, north side - 240404.jpg|Tuned mass damper
</gallery>