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The Millennium Bridge, officially known as the London Millennium Footbridge, is a steel suspension bridge for pedestrians crossing the River Thames in London, 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 in June 2000.
Londoners nicknamed it the “Wobbly Bridge” after pedestrians experienced an alarming swaying motion on its opening day. 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.
The design of the bridge was the subject of a competition organised in 1996 by Southwark council and RIBA Competitions. The winning entry was an innovative “blade of light” effort from Arup Group, Foster and Partners, and Sir 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 is made of three main sections of 81 m (266 ft), 144 m (472 ft), and 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 on the bridge at one time.
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. Construction began in late 1998 and the main works were started on 28 April 1999 by Monberg & Thorsen and Sir Robert McAlpine. The bridge was completed at a cost of £18.2 million (£2.2M over budget), primarily paid for by the Millennium Commission and the London Bridge Trust.
The bridge opened on 10 June 2000, two months late.
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.
Vibration was attributed to an under-researched phenomenon whereby pedestrians crossing a bridge that has a lateral sway have an unconscious tendency to match their footsteps to the sway, exacerbating it. The tendency of a suspension bridge to sway vertically when troops march over it in step was well known, which is why troops are required to break step when crossing such a bridge. An example is London’s Albert Bridge, which has a sign dating from 1873 warning marching ranks of soldiers to break step while crossing.
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; the maximum sway was around 70mm. 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 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. 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:
Auckland Harbour Bridge, with a lateral frequency of 0.67 Hz during a 1975 demonstration
Birmingham NEC Link bridge, with a lateral frequency of 0.7 Hz
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.
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. 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. Additionally, 52 tuned mass dampers add inertia to control vertical movement. The work took from May 2001 to January 2002 and cost £5M. After a period of testing, the bridge was reopened on 22 February 2002 and has not been subject to significant vibration since. In spite of the successful cure, the affectionate “wobbly bridge” (sometimes “wibbly-wobbly”) epithet remains in common usage among Londoners.
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 museum 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.
In popular culture
The Bridge is featured in Harry Potter and the Half-Blood Prince, where the bridge collapses following an attack by Death Eaters.
The Bridge appears in the 2014 Marvel Cinematic Universe film Guardians of the Galaxy during the climactic battle on Xandar.
The Bridge appears in the Olly Murs music video Heart on My Sleeve.
The bridge appears in the anime adaptation of The Ancient Magus’ Bride.
The bridge appears in the BBC One’s television film The 7:39.
The bridge is featured in shots from Taylor Swift’s ‘End Game’ music video (2018).
The bridge is featured in shots from One Direction’s Midnight Memories music video (2014).
Two dancers perform on the bridge in the music video of Breathe by Jax Jones.
The bridge is briefly featured in the Julian Barnes 2011 Man Booker Prize-winning novel “The Sense of an Ending”.
The bridge is briefly shown at the end of a Netflix Original Show, Black Mirror, in Season 1, Episode 1 (“The National Anthem”) after the Prime Minister was forced to commit sexual acts with a pig on live TV in order to get a princess back from an extremist group.
(Wikipedia)
Die Millennium Bridge ist eine Fußgängerbrücke über die Themse in London. Sie verbindet die City of London auf der Nordseite mit dem Stadtteil Southwark im Stadtbezirk London Borough of Southwark auf der Südseite. Die Brücke ist im Besitz von Bridge House Estates, einer Wohlfahrtsorganisation der City of London Corporation.
Am nördlichen Ende der Brücke befinden sich die St Paul’s Cathedral und die City of London School, am südlichen Ende das Tate Modern, das Globe Theatre und die Bankside Gallery. Die erdverankerte Hängebrücke ist so ausgerichtet, dass man vom südlichen Ufer aus einen uneingeschränkten Blick auf die St Paul’s Cathedral genießt.
1996 veranstaltete die Stadtbezirksverwaltung von Southwark einen Architekturwettbewerb. Das siegreiche Projekt stammte von Norman Foster (Entwerfer), Arup (Ingenieurbüro), Chris Wise (Ingenieur bei Arup für die ursprünglichen Pläne) und Anthony Caro. Wegen der Beschränkung der Höhe und um die Aussicht zu verbessern, befinden sich die Tragseile neben dem Fußweg, wodurch die Hängebrücke ungewöhnlich flach erscheint. Die Brücke steht auf zwei Säulen und besitzt drei Sektionen mit einer Länge von 81, 144 und 108 Meter (von Nord nach Süd); die gesamte Länge der Brücke beträgt 325 Meter. Die acht Tragseile können ein Gewicht von 2000 Tonnen tragen, dadurch können sich gleichzeitig 5000 Personen auf der Brücke aufhalten.
Die Vorarbeiten begannen im Juli 1998, die Hauptarbeiten am 28. April 1999. Die Brücke kostete 18,2 Millionen Pfund (2,2 Millionen über dem Budget) und wurde am 10. Juni 2000 mit zwei Monaten Verspätung eröffnet. Nur zwei Tage später musste sie wegen unkontrollierten heftigen Schwankens wieder für den Publikumsverkehr geschlossen werden. Dabei handelte es sich im Wesentlichen um seitliche Bewegungen. Die vertikalen Bewegungen blieben dagegen im vorausberechneten Rahmen. Die Brücke bekam daraufhin von den Einwohnern Londons den Spitznamen The wobbly bridge (Wackelbrücke).
Umfangreiche theoretische Untersuchungen und praktische Tests ergaben folgende Erklärung:
Die erste Eigenfrequenz für Querschwingungen der Brücke liegt bei etwa 1 Hertz. Daher ist es für Fußgänger durchaus möglich, sie zum Schwingen anzuregen. Im Allgemeinen laufen Personen auf einer Brücke nicht im Gleichschritt. Wenn jedoch zufällig die Brücke einmal in Querschwingungen gerät, passen sich die Menschen dieser Schwingung an und versuchen, diese durch ihre eigene Bewegung auszugleichen, etwa so, wie ein Seemann sich auf einem schwankenden Schiff bewegt. Damit bewegen sie sich gleichförmig und verstärken so die Schwingung. Dies geschieht weitgehend unbewusst. Erst wenn die Schwingungen so groß geworden sind, dass sie als unangenehm oder bedrohlich empfunden werden, bleiben die Menschen stehen und halten sich, wenn möglich, am Geländer fest. Dadurch hört die Schwingung wieder auf.
Zur Sanierung baute man in den folgenden zwei Jahren ein spezielles Dämpfersystem in die Millennium Bridge ein. Dieses besteht im Wesentlichen aus unter einigen Brückenfeldern diagonal verlegten Dämpfern und insgesamt 58 Schwingungstilgern, die horizontal und vertikal mit der Brücke verbunden wurden. Die Nachrüstung der Brücke verursachte Kosten in Höhe von 5 Millionen Pfund. Die Arbeit an den Korrekturen leitete Arup Tony Fitzpatrick.
Am 22. Februar 2002 wurde die Millennium Bridge wieder für den Publikumsverkehr geöffnet. Die Erfahrungen mit dem unerwarteten „Eigenleben“ der Brücke führten zu umfassenden Nachuntersuchungen anderer Brückenkonstruktionen, da man den Horizontalschwingungen in dieser Form im Brückenbau bis zum Jahr 2000 nicht ausreichend Beachtung geschenkt hatte.
Im März 2008 wurde die Millennium Bridge für zwei Tage gesperrt, um Dreharbeiten für den Film Harry Potter und der Halbblutprinz durchzuführen; im Film wird die Brücke zerstört.
(Wikipedia)
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