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 sited between Southwark Bridge and Blackfriars Railway Bridge.
The Millennium Bridge is owned and maintained by Bridge House Estates, a charitable trust
overseen by the City of London Corporation. Construction of the bridge began in 1998,
with the opening in June 2000. Londoners nicknamed the bridge the "Wobbly
Bridge" after participants in a charity walk on behalf of Save the Children to open the
bridge felt an unexpected and, for some, uncomfortable swaying motion on the first two days after
the bridge opened. The bridge was closed later that day, and after two days of limited access
the bridge was closed for almost two years while modifications were made to eliminate
the wobble entirely. It reopened in 2002. The southern end of the bridge is near the
Globe theatre, the Bankside Gallery and Tate Modern, the north end next to the City of
London School below St Paul's Cathedral. The bridge alignment is such that a clear view
of St Paul's south façade is presented from across the river, framed by the bridge supports.
Design The design of the bridge was the subject of
a competition organized in 1996 by Southwark council and RIBA Competitions. The winning
entry was an innovative "blade of light" effort from Arup, 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 metres, 144 metres and 108
metres with a total structure length of 325 metres; the aluminium deck is 4 metres 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. Construction
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 obtaining
planning permissions from the City of London and London Borough of Southwark. 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 £18.2M, primarily paid for by
the Millennium Commission and the London Bridge Trust. It opened on 10 June 2000.
Unexpected lateral vibration 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 and dampened neither public enthusiasm for what was something of a white-knuckle
ride, nor the vibrations themselves. The closure of the bridge only two days after opening
attracted public criticism of it as another high-profile British Millennium project suffered
an embarrassing setback, akin to how many saw the Millennium Dome. The wobble 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, thereby exacerbating
the sway. The tendency of a suspension bridge to sway when troops march over it in step
was well known, which is why troops are required to break step when crossing such a bridge.
The bridge was temporarily closed on 18 January 2007, during the Kyrill storm due to strong
winds and a risk of pedestrians being blown off the bridge.
Resonance
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. 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 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, the vibrational modes had not been anticipated by the designers.
The crucial point is that when the bridge lurches to one side, the pedestrians must
adjust to keep from falling over, and they all do this at exactly the same time. Hence
the situation is similar to soldiers marching in lockstep, but horizontal instead of vertical.
The lateral vibration problems of the Millennium Bridge are very unusual, but not entirely
unique. 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. For example, Albert Bridge
in London has a sign dating from 1873 warning marching ranks of soldiers to break step while
crossing. Other bridges which have seen similar problems are:
Birmingham NEC Link bridge, with a lateral frequency of 0.7 Hz
Groves Suspension Bridge, Chester, in 1977 during the Jubilee river regatta
Auckland Harbour Road Bridge, with a lateral frequency of 0.67 Hz, during a 1975 demonstration
After extensive analysis by the engineers, the problem was fixed by the retrofitting
of 37 fluid-viscous dampers to control horizontal movement and 52 tuned mass dampers to control
vertical movement. This took from May 2001 to January 2002 and cost £5M. After a period
of testing, the bridge was successfully re-opened on 22 February 2002. The bridge has not been
subject to significant vibration since. In spite of the successful fix of the problem,
the affectionate "wobbly bridge" 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 Millennium Bridge was featured in the
sixth installment of the Harry Potter film franchise, where the bridge collapsed following
an attack by Death Eaters. The Bridge also appeared in the 2014 Marvel
Cinematic Universe film Guardians of the Galaxy during the climactic battle on Xandar.
The Bridge also appeared in the video to the Olly Murs song "Heart on My Sleeve."
See also London Millennium Funicular, a very small
funicular railway situated in the City of London, immediately to the east of the northern
end of the Millennium Bridge Angers Bridge
Brooklyn Bridge—Pedestrian access Tacoma Narrows Bridge, the original Tacoma
Narrows Bridge that collapsed in 1940 Tay Bridge disaster
References Notes
Bibliography
External links Millennium Bridge at Structurae
Arup's Millennium Bridge site A PDF paper from Arup, discussing the engineering
and resonance of the bridge. A paper from Taylor Devices Inc on the dampers
retrofitted to the bridge Information about the GERB TMDs retrofitted
to the bridge. Brooklyn Bridge: lateral S-shaped vibration
= pedestrian oscillations or "sway" A Cambridge University Engineering Department
account of the Millennium Bridge problem.