the millennium bridge
The Millennium Bridge
The Millennium Bridge, one of London’s major attractions, opened on June 10 (David Newland) after the world observed the passing of the millennium (T.R. Reid). The thin silver bridge was built to link the St. Paul’s Cathedral, located on the north bank of the Thames River, and the Globe Theater of Shakespeare on the south part, crossing the width of the Thames River (T.R. Reid). The $29 million (T.R. Reid), 330 meter span connected London with the Tate Modern Gallery located at Bankside (Urban 75). Merging adventuresome design ideas, the bridge was framed as a suspension bridge with the cables holding the bridge located underneath rather than above the bridge (T.R. Reid).
The design of the bridge at the time was greeted by people in architecture circles as a great achievement to the engineering expertise of the British (T.R. Reid). It was made with the intent of becoming a showcase of the gains of technology at the beginning of the new millennium (University of North Carolina-Charlotte). When it was constructed, the bridge was one of a kind, with no other structure like it (North Carolina-Charlotte). It was so revolutionary that the bridge design won the competition organized by the Southwark Council in 1996 (North Carolina-Charlotte) and the Financial Times and the British Royal Institute of Architecture (Urban 75).
The work on the bridge began in February 1999 on the site of an abandoned jetty for the power facility at Bankside, the jetty being demolished to make way for the construction of the bridge (Urban 75). Using the latest design concepts, the bridge’s profile would be at least six times shallower than the suspension bridge technology currently employed (Urban 75). As the bridges’ location was a historical site, archaeological activities were done before the actual excavation works on either bank of the bridge began (Urban 75). On the bridges’ opening day, approximately 80,000 to 100,000 people crossed the span (Urban 75).
According to the chief proponent of the construction of the bridge, engineering firm Arup, The Company did not prepare that the people walking on the bridge would fall into a synchronized beat (Michael Crosbie). As the bridge swung like a pendulum, the people on the bridge adjusted their walking; this further amplified the swinging (T.R. Reid). At first, authorities tried to reduce the number of people using the bridge (T.R. Reid). As the swing grew worse, the people on the bridge resembled first-time ice skaters (Cornell University). They would plant their feet wide, swishing left and right to get across (Cornell University).
As stated earlier, the rhythmic pace of the bridge crossers was not intentional (Cornell University). Even though the bridge’s design allowed it to compensate for a certain amount of movement, it was clear from the start that something was not right with the bridge (Urban 75). Senior citizens on the bridge clasped firmly on the hand rails on the bridge. People were complaining of sea sickness. The $32 million triumph of what the British called as an expression of engineering and even a “blade of light” (T.R. Reid) was fast becoming a very costly carnival attraction (Urban 75).
The “Wobbly Bridge”
The Millennium Bridge was lumped together with the infamous Millennium Dome as one of the great failures of architecture at the turn of the century (Global Architecture Encyclopedia). The original visage for the project was that of a lustrous link between London and the Southwark borough across the River Thames (Global). In the aspect of execution of the design and construction, the bridge was a sight to behold, but upon its opening, the problems reared themselves almost immediately (Global). As the bridge swayed, the new perception changed into one of fear that the British harbor against the introduction of new technology (T.R. Reid). Hence, British media have adorned the Millennium Bridge with another moniker- the “Wobbly Bridge” (Urban 75).
The British press went on a feeding frenzy about the embarrassment (Urban 75). Parliament was besieged with inquiries about the structure (Urban 75). The British people, however, took a different tack. They believed that the bridge was another “white elephant’ lying across the Thames (Urban 75). The explanation of Arup, that the fault lay with the people walking in rhythm, further fuelled the controversy (Crosbie).
After the “carnival ride” that the bridge crossers experienced in walking on the bridge, the bridge was closed almost instantly as it opened (Urban 75). What did happen to the bridge for it to sway in such a violent fashion? Cornell University theoretical and applied mechanics professor Steve Strogatz tries to offer some explanations why the bridge gave a new meaning to the term “Swinging London” (T.R. Reid). According to Strogartz (2005), the problem lay in the bridge design as well as the crowd on the bridge (Steve Strogartz).
The bridge itself had been tested and passed requirements for wind and tonnage factors (Cornell University). The bridge was tested for every factor that did not involve humans (Cornell University). But, according to Strogartz (2005), the problem lay with the humans (Cornell University). Instead of focusing on the perceived structural deficiencies of the bridge as the key to the solution to the dilemma, the problem of the synchronized walking of the people crossing the bridge was noted (Cornell University).
When it was necessary for military infantry to cross structures such as bridges, the troops were ordered to “break cadence”, or to break the rhythm that they observe when making marches (Cornell University). The reason for this is that the rhythmic march on a bridge would create enough force vertically to destroy a bridge (Cornell University). When the crowd made their way across the bridge, the structure began to display a sudden lateral swaying movement on the deck of the structure (Newland). The people set off a frightening 70 millimeter jiggle of the bridge (Lune Millennium Bridge).
But the actions of the pedestrians cannot be compared to the marching troops that crossed bridges (Cornell University). As was stated earlier, the bridge swayed, in a horizontal fashion, rather than a vertical fashion (Cornell University). As such, there was no deliberate attempt on the part of the pedestrians to walk in cadence to cross the bridge. The pedestrians only did so to remedy their imbalance on the bridge (Cornell University). According to Strogatz (2005), the bridge already possessed some inherent structural inadequacies (Cornell University).
Strogatz (2005) explains that the bridge was designed to be flexible; hence the structure would be more attuned to walking purposes (Cornell University). If this view was considered, all that would take to make the bridge vibrate was a few people on the structure (Cornell University). The number that was tested by Strogatz and his colleagues was a measly 160 (Cornell University). This is radically low compared to the number of people that crossed the bridge on opening day, estimated at around 80,000 people, with 2,000 people on the structure at any one time (Cornell University).
Ove Arup, the engineering firm that designed the bridge, also conducted its own set of tests on the faults noted on the structure (Newland). In the course of their research, the teams found several similar cases to the Millennium bridge problem (Newland). Their research bore out a report about a foot bridge in Germany that also showed a strong sway when it opened with approximately 300 to 400 individuals crossing (Newland). The problem discovered by the Arup teams showed that a large number of people moved sideways in synchronization to remedy the minute, natural sideways motion of the bridge (Lune).
This sideways motion went previously undetected in the previous testing and owed it to the bridges’ unique built (Lune). The extra movement of the people “locked in” to the bridge’s natural frequency, hence the violent swaying motion of the bridge (Lune). As the people walked across the bridge, the girders of the bridge increased their movements as the number of lateral movements of the people on the deck increased (Newland). When the pedestrians, alarmed at the swaying of the bridge, moved in a unitary motion, the motion of the bridge increased as the unison motion of the people on the bridge increased (Newland).
Repairing the bridge
The series of tests on the bridge showed that the adoption of “passive damping” systems was the optimal way of intervention for the bridge (Urban 75). Two types of damping processes were used for the bridges’ repair, viscous dampers and the Turned Mass Dampers (Urban 75). These damping systems would absorb the energy generated by the movements of the structure (Urban 75). The viscous dampers were lodged in the bridges’ central span in the middle of the deck of the bridge and the horizontal span (Crosbie).
The X-shaped dampers would be the ones responsible to combat the lateral movements of the bridge (Crosbie). These devices installed under the bridges’ deck, encircling the piers and at the south bank of the bridge (Urban 75). They manage the lateral swaying motion of the bridge, like shock absorbers (Urban 75). The turned mass dampers are equipped with springs installed at the underside of the walkway of the bridge and the transverse arms of the structure (Crosbie).
These devices are designed to control the bridges’ vertical movements (Urban 75). All in all, the bridge required the installation of 37 viscous dampers and 54 turned mass dampers for the repair of the bridge (Crosbie). The extra modifications on the bridge cost an additional $8.9 million (Cornell). As the construction of the bridge was underway, the visitors to the site were treated to hundreds of volunteers, all paid, walking across the structure, as a group of engineers tried to correct the sway of the bridge (Urban 75).
The fears of the public that the Millennium bridge was going to be another failure of British engineering was not lost on them (BBC News). The British government had spent millions of extra money just to keep the Millennium Dome afloat because of low attendance rates (BBC News). The huge Ferris wheel the London Eye, overlooking the Houses of Parliament, was late by a month when it finally opened (BBC News). But after twenty long months and a huge amount in repairs, the newly refurbished Millennium Bridge finally reopened (T.R.Reid).
It was said that if the wobble problem that beset the bridge from the beginning could be adequately answered, the bridge would be a resounding triumph (Global). And a success the bridge did become. After a most controversial start, the bridge has proved to be a most valuable asset to the London society, serving both as a tourist attraction and as a means of shorter travel time between the cherished Saint Paul’s Cathedral and the Shakespearean Globe Theater (T.R.Reid). The Millennium bridge issue gives us all reminders on the relationship of people and technology (Crosbie).
One of the main ideas behind the construction of the bridge was to make it a showcase for the new millennium (North Carolina- Charlotte). But the question is: Did the technical corrections on the bridge make it a “Leaning Tower of Pisa” without the lean (Crosbie)? It is quite the opposite. It just reminds us for the need for humility in spite of the technological advances we have at our disposal (Crosbie).
BBC News. “London’s Millennium Bridge to close”.
Cornell University. “Explaining why the Millennium Bridge wobbled”.
Crosbie, Michael J. “London’s Bridge Ascendant”.
Global Architecture Encyclopedia. “Architecture of the Millennium bridge-London, England”.
Lune Millennium Bridge. “London”.
Newland, David E. “Vibration of the London Millennium footbridge: part 1”.
Reid, T.R. “London Opens Millennium Bridge”. Washington Post 22 February 2002
Strogatz, Steve. “London Opens Millennium Bridge”.
University of North Carolina-Charlotte. “Millennium Bridge”
Urban 75. “Millennium Bridge over the River Thames, joining the Tate Modern and St. Paul’s London”.