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Millennium Bridge, London

(Redirected from Wobbly bridge)

The Millennium Bridge, officially known as the London Millennium Footbridge, is a steel suspension bridge for pedestrians crossing the River Thames in London, England, linking Bankside with the City of London. It is owned and maintained by Bridge House Estates, a charitable trust overseen by the City of London Corporation. Construction began in 1998, and it initially opened on 10 June 2000.

Millennium Bridge
The bridge seen from St Paul's Cathedral.
Coordinates51°30′37″N 0°05′54″W / 51.510173°N 0.098438°W / 51.510173; -0.098438
CarriesPedestrians
CrossesRiver Thames
LocaleLondon, England
Official nameLondon Millennium Footbridge
Maintained byBridge House Estates,
City of London Corporation
Preceded byBlackfriars Railway Bridge
Followed bySouthwark Bridge
Characteristics
DesignSuspension bridge
Total length325 metres (1,066 ft)
Width4 metres (13 ft)
Longest span144 metres (472 ft)
History
Engineering design byArup
Constructed byMonberg & Thorsen
Sir Robert McAlpine
Opened10 June 2000; 24 years ago (2000-06-10)
Location
Map

Londoners nicknamed it the "Wobbly Bridge" and even the "Wibbly Wobbly" after pedestrians experienced an alarming swaying motion on its opening day.[1][2] The bridge was closed later that day and, after two days of limited access, it was closed again for almost two years so that modifications and repairs could be made to keep the bridge stable and stop the swaying motion. It reopened in February 2002.

The bridge is located between Southwark Bridge and Blackfriars Railway Bridge. Its southern end is near the Globe Theatre, the Bankside Gallery, and Tate Modern, while its northern end is next to the City of London School below St Paul's Cathedral. The bridge's alignment is such that a clear view (i.e. a "terminating vista") of St Paul's south façade is presented from across the river, framed by the bridge supports.

Design

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An Architectural design competition was organised in 1996 by Southwark council and RIBA Competitions. The winning entry was an innovative "blade of light" effort from Arup Group, Foster + Partners and Anthony Caro. Due to height restrictions, and to improve the view, the bridge's suspension design had the supporting cables below the deck level, giving a very shallow profile. The bridge has two river piers and consists of three main sections of 81 m (266 ft), 144 m (472 ft), , 108 m (354 ft) (north to south) with a total structure length of 325 m (1,066 ft); the aluminium deck is 4 m (13 ft) wide. The eight suspension cables are tensioned to pull with a force of 2,000 tons against the piers set into each bank—enough to support a working load of 5,000 people.

 

Construction

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Millennium Bridge
 
Millennium Bridge at night, showing the much-photographed illusion of St. Paul's Cathedral being supported by one of the bridge supports

Ordinarily, bridges across the River Thames require an Act of Parliament. For this bridge, that was avoided by the Port of London Authority granting a licence for the structure, and the City of London and London Borough of Southwark granting planning permission.[3] Construction began in late 1998, and the main works were started on 28 April 1999 by Monberg & Thorsen and Sir Robert McAlpine.[4] The eventual cost was £18.2 million (£2.2m over budget), primarily paid for by the Millennium Commission and the London Bridge Trust.[5]

Opening

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The bridge opened on 10 June 2000, one month late.[6]

Unexpected lateral vibration due to resonant structural response caused the bridge to be closed on 12 June for modifications. Attempts had been made to limit the number of people crossing the bridge, which led to long queues but were ineffective to dampen the vibrations. Closure of the bridge only two days after opening attracted public criticism as another high-profile British Millennium project that suffered an embarrassing setback, akin to how many saw the Millennium Dome.

The vibration was attributed to a then-underresearched phenomenon[7] whereby pedestrians crossing a bridge that has a lateral sway have an unconscious tendency to match their footsteps to the sway, exacerbating it. This is different from the well-understood problem of vertical sway, which is why troops stop marching in stride together as a unit when crossing such a bridge.[8] An example is London's Albert Bridge, which has a sign dating from 1873 warning marching ranks of soldiers to break step while crossing.[9]

Resonance

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The bridge's movements were caused by a positive feedback phenomenon, known as synchronous lateral excitation. The natural sway motion of 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;[10][11] the maximum sway was around 70 millimetres (2.8 in).[12] On the day of opening, the bridge was crossed by 90,000 people, with up to 2,000 on the bridge at a time.

Resonant vibrational modes due to vertical loads (such as trains, traffic or pedestrians) and wind loads are well understood in bridge design. In the case of the Millennium Bridge, because the lateral motion caused pedestrians to directly participate with the bridge, the vibrational modes had not been anticipated by the designers. When the bridge lurches to one side, the pedestrians must adjust to keep from falling over, and they all do this at the same time. The effect is similar to soldiers marching in lockstep, but horizontal instead of vertical.

The risks of lateral vibration in lightweight bridges are well known.[13] Any bridge with lateral frequency modes of less than 1.3 Hz, and sufficiently low mass, could witness the same phenomenon with sufficient pedestrian loading. The greater the number of people, the greater the amplitude of the vibrations. Other bridges which have seen similar problems are:

Mitigation

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Engineers at 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.[12]

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.[12] Instead, the resonance was controlled by retrofitting 37 viscous fluid 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.[15][16] Additionally, 52 tuned mass dampers 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"[17]) epithet remains in common usage among Londoners.[18][19]

  • Dampers
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    Chevron dampers
  •  
    Vertical to ground dampers
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    Pier dampers
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    Moving end of pier damper
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    Tuned mass damper

Cable resonance

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An artistic expression of the higher-frequency resonances within the cables of the bridge were explored by Bill Fontana's Harmonic Bridge exhibition at the Tate Modern in mid-2006. This used acoustic transducers placed at strategic locations on the cabling of the Millennium Bridge and the signals from those transducers were amplified and dynamically distributed throughout the Turbine Hall of the Tate by a programme which Fontana entered into the sound diffusion engine of the Richmond Sound Design AudioBox.[20]

Repair

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In October 2023, the bridge was closed for three weeks to allow repairs to its surface, undertaken by FM Conway.[21] The bridge closed on Saturday 14 October[22] and reopened late on 5 November.[23]

Millennium Inclinator

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Onboard view of the Millennium Inclinator

A short inclined lift, known as the Millennium Inclinator, is next to the northern end of the Millennium Bridge. It was opened in December 2003 to allow pedestrians to surmount the steep slope (13.6°) of Peter's Hill from the riverside to the entrance to the Millennium Bridge without using the alternative flight of steps.[24][25] The lower end of the lift is on Paul's Walk next to the Thames, and the top end is 26.85 metres (88.1 ft) further up Peter's Hill on the terrace which is level with the deck of the bridge.[24][25] It was primarily installed for use by those who cannot easily manage the steep steps, such as people with disabilities and parents with push chairs.[26]

The lift carriage was originally powered by an electric traction motor, manufactured in Italy by Maspero Elevatori, with a speed of 0.5 metres per second (1.6 ft/s) and a maximum capacity of 0.7 metric tons (0.77 short tons; 0.69 long tons).[24][25] However, by 2010 the City of London Planning and Transportation Committee decided that the level of service was unacceptable, because the inclinator was frequently out of service due to mechanical breakdowns and vandalism. So the Committee agreed it would be replaced at a cost of up to £750,000 in time for the 2012 Summer Paralympics.[26]

A major renovation project was undertaken in 2012, and the lift was reopened in time for the Thames Diamond Jubilee Pageant of 3 June 2012, which took place about a month before the 2012 Summer Olympics. The new lift was manufactured by Hütter Aufzüge of Glinde, Schleswig-Holstein, Germany, a lift manufacturer which was taken over by Otis in 2013.[27] Axis Elevators installed the new equipment.[28] Following a redevelopment of the area in 2021 the lift was closed and will be replaced by a platform lift.

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Underside of bridge from Southbank
 
Millennium Bridge and River Thames, looking north
 
Showing the cable suspension system.
 
The view east from the Millennium Bridge

See also

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References

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Millennium Bridge, London, United Kingdom, 2020
Notes
  1. ^ "Millennium Bridge London". Britain Visitor - Travel Guide To Britain. 15 August 2020. Retrieved 11 August 2023.
  2. ^ "London Millennium Footbridge London". Guide London. 15 November 2023. Retrieved 12 April 2024.
  3. ^ Thames Bridges – Neil Davenport[page needed]
  4. ^ Where Thames Smooth Waters Glide
  5. ^ Life: The Observer Magazine – A celebration of 500 years of British Art – 19 March 2000
  6. ^ "Queen dedicates Millennium Bridge". BBC News. 9 May 2000. Retrieved 1 February 2023.
  7. ^ "Before the Millennium Bridge, the math of "synchronous lateral excitation" from pedestrians was not at all well-understood. Once the bridge had been fixed, it was a well-investigated area." -- Humble Pi: When Math Goes Wrong In The Real World, by Matt Parker, page 274
  8. ^ Jeans, James (1923). Science and Music. Cambridge University Press. p. 56.
  9. ^ "All troops must break step on Albert Bridge". Archived from the original on 25 January 2014.
  10. ^ Josephson, Brian (14 June 2000). "Out of step on the bridge". The Guardian. Retrieved 22 March 2018.
  11. ^ Strogatz, Steven et al. (2005). "Theoretical mechanics: Crowd synchrony on the Millennium Bridge", Nature, Vol. 438, pp. 43–44.
  12. ^ a b c "The Millennium Bridge: Challenge". Arup. Archived from the original on 31 December 2008.
  13. ^ Julavitz, Robert. "Point of Collapse", Archived 17 June 2008 at the Wayback Machine Village Voice, 26 August 2003.
  14. ^ Dallard, P. et al. "The London Millennium Footbridge," Archived 27 September 2011 at the Wayback Machine Structural Engineer, 20 November 2001. 79:22, pp. 17–35.
  15. ^ Taylor, Douglas P. Damper Retrofit of the London Millennium Footbridge - A Case Study in Biodynamic Design (PDF). Taylor Devices, Inc. Retrieved 14 March 2019.
  16. ^ Klembczyk, Alan R. A Study in the Long-Term Performance of Specialized Low Friction Hermetically Sealed Fluid Viscous Dampers Under Nearly Continuous Operation on a Pedestrian Bridge (PDF). Taylor Devices, Inc. Retrieved 14 March 2019.
  17. ^ E.g., "The Wibbly Wobbly Millennium Bridge in London", YouTube; accessed 20 August 2021
  18. ^ "Millennium Bridge over the River Thames, joining the Tate Modern and St Paul's London – photos, history and background". Urban75.org. Retrieved 26 March 2013.
  19. ^ Lydall, Ross (27 October 2009). "Second wobbly bridge for London". Evening Standard. Archived from the original on 30 October 2009. Retrieved 26 March 2013.
  20. ^ The sound sculptures and ideas of Bill Fontana Resoundings
  21. ^ Dale, Sarah (25 October 2023). "Catch net installed to soffit of Millennium Bridge to facilitate planned maintenance work". Infrastructure Intelligence. Retrieved 26 October 2023.
  22. ^ "Millennium Bridge: 'Wobbly' pedestrian crossing to close for repairs". BBC News. 5 October 2023. Retrieved 6 October 2023.
  23. ^ "Millennium Bridge Reopens after Three-week Closure". City Bridge Foundation. November 2023. Retrieved 5 March 2024.
  24. ^ a b c "Ride the London Millennium Funicular". Tired of London, Tired of Life. 4 October 2010. Retrieved 12 April 2013.
  25. ^ a b c Hows, Mark (5 December 2003). "London Millennium Funicular". Hows.org.uk. Retrieved 5 April 2013.
  26. ^ a b Bloomfield, Ruth (19 November 2010). "Millennium Bridge throws another wobbly as 'erratic' disabled lift must have £750,000 replacement". Evening Standard. Retrieved 12 April 2013.
  27. ^ Stürmlinger, Daniela (20 November 2015). "Hütter-Aufzüge in Glinde droht das Aus" (in German). Hamburger Abendblatt. Retrieved 25 June 2020.
  28. ^ "The Millennium Bridge Inclined Lift". Dunbar and Boardman. 18 October 2012. Retrieved 12 April 2013.
  29. ^ "Harry Potter Film Locations in London – Millennium Bridge". Golondon.about.com. 5 March 2014. Retrieved 10 July 2014.
  30. ^ Shahid, Sharnaz (11 August 2013). "Guardians Of The Galaxy Cast Get Physical In London Shoot". Entertainmentwise. Archived from the original on 2 December 2014. Retrieved 11 August 2013.
Bibliography
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