Millennium Bridge | |
|---|---|
 The bridge seen fromSt Paul's Cathedral. | |
| Coordinates | 51°30′37″N0°05′54″W / 51.510173°N 0.098438°W /51.510173; -0.098438 |
| Carries | Pedestrians |
| Crosses | River Thames |
| Locale | London, England |
| Official name | London Millennium Footbridge |
| Maintained by | Bridge House Estates, City of London Corporation |
| Preceded by | Blackfriars Railway Bridge |
| Followed by | Southwark Bridge |
| Characteristics | |
| Design | Suspension bridge |
| Total length | 325 metres (1,066 ft) |
| Width | 4 metres (13 ft) |
| Longest span | 144 metres (472 ft) |
| History | |
| Engineering design by | Arup |
| Constructed by | Monberg & Thorsen Sir Robert McAlpine |
| Opened | 10 June 2000; 24 years ago (2000-06-10) |
| Location | |
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TheMillennium Bridge, officially known as theLondon Millennium Footbridge, is a steelsuspension bridge for pedestrians crossing theRiver Thames in London, England, linkingBankside with theCity of London. It is owned and maintained byBridge House Estates, a charitable trust overseen by theCity of London Corporation. Construction began in 1998, and it initially opened on 10 June 2000.
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 betweenSouthwark Bridge andBlackfriars Railway Bridge. Its southern end is near theGlobe Theatre, theBankside Gallery, andTate Modern, while its northern end is next to theCity of London School belowSt 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.
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Anarchitectural design competition was organised in 1996 bySouthwark council andRIBA Competitions. The winning entry was an innovative "blade of light" effort fromArup Group,Foster + Partners andAnthony Caro.[3] Due toheight 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 aworking load of 5,000 people.
Ordinarily, bridges across the River Thames require an Act of Parliament. For this bridge, that was avoided by thePort of London Authority granting a licence for the structure, and theCity of London andLondon Borough of Southwark grantingplanning permission.[4] Construction began in late 1998, and the main works were started on 28 April 1999 byMonberg & Thorsen andSir Robert McAlpine.[5] The eventual cost was £18.2 million (£2.2m over budget), primarily paid for by theMillennium Commission and the London Bridge Trust.[6]
The bridge opened on 10 June 2000, one month late.[7] Unexpected lateral vibration due toresonant 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 longqueues 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 theMillennium Dome.
The vibration was attributed to a then under researched phenomenon[8] whereby pedestrians crossing a bridge that has alateral sway have an unconscious tendency to match their footsteps to the sway, exacerbating it. This is different from the well-understood problem ofvertical sway, which is why troops stop marching in stride together as a unit when crossing such a bridge.[9] An example is London'sAlbert Bridge, which has a sign dating from 1873 warningmarching ranks of soldiers to break step while crossing.[10]
The bridge's movements were caused by apositive feedback phenomenon, known assynchronous lateral excitation. The natural sway motion of people walking caused small sidewaysoscillations in the bridge, which in turn caused people on the bridge to sway in step, increasing theamplitude of the bridge oscillations and continually reinforcing the effect;[11][12] the maximum sway was around 70 millimetres (2.8 in).[13] 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.[14] 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:
Engineers atArup, 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 theUniversity of Southampton andImperial College London. Later in 2000, one span of the bridge was instrumented and tested with crowds of up to 275 people.[13]
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.[13] Instead, the resonance was controlled by retrofitting 37 viscous fluiddampers 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.[16][17] Additionally, 52tuned 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"[18]) epithet remains in common usage among Londoners.[19][20]
An artistic expression of the higher-frequency resonances within the cables of the bridge were explored by Bill Fontana'sHarmonic 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 theRichmond Sound Design AudioBox.[21]
In October 2023, the bridge was closed for three weeks to allow repairs to its surface, undertaken byFM Conway.[22] The bridge closed on Saturday 14 October[23] and reopened late on 5 November.[24]
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A shortinclined lift, known as theMillennium 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.[25][26] The lower end of the lift is on Paul's Walk next to theThames, 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.[25][26] It was primarily installed for use by those who cannot easily manage the steep steps, such as people with disabilities and parents withpush chairs.[27]
The lift carriage was originally powered by an electrictraction 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 0.7metric tons (0.77short tons; 0.69long tons).[25][26] 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 the2012 Summer Paralympics.[27]
A major renovation project was undertaken in 2012, and the lift was reopened in time for theThames Diamond Jubilee Pageant of 3 June 2012, which took place about a month before the2012 Summer Olympics. The new lift was manufactured byHütter Aufzüge ofGlinde, Schleswig-Holstein, Germany, a lift manufacturer which was taken over byOtis in 2013.[28] Axis Elevators installed the new equipment.[29]Following a redevelopment of the area in 2021 the lift was closed and will be replaced by a platform lift.
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Bridges of Central London(west to east) | ||
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