Millennium Bridge 20 Years On: How Cleveland Bridge Group stepped in to save a London landmark
A postcard perennial, the Millennium Bridge is an instantly-recognisable London landmark that has appeared in countless television programmes, music videos and even one Harry Potter film.
And, while we did not construct the bridge itself, Cleveland Bridge Group played a vital role that ensured future generations could enjoy this iconic structure.
To celebrate the Millennium Bridge’s 20th anniversary, we decided to take a look back on this rehabilitation work that saved the bridge from closing down after just one weekend.
Continue reading, below, to find out more.
When the Millennium Bridge first opened in June 2000, it became Central London’s first new river crossing for more than 100 years, linking Bankside with the City of London. However, this historic opening was short-lived.
On its opening day, pedestrians reported an ‘alarming swaying’ while crossing the structure. The bridge was temporarily closed for the day, only opening at a limited capacity for the following two days. Consequently, the decision was made to close the bridge until the necessary repairs could be made; just 3 days after its grand opening.
But what caused the Millennium Bridge to sway so alarmingly? The engineers who inspected the bridge concluded that the sideways movement was caused by the synchronised effect of thousands of people stepping in unison. (It was reported that around 2,000 people were crossing the bridge at any one time on the first day.)
This heavy footfall resulted in an engineering phenomenon known as ‘positive feedback’. The natural sway of people walking caused small sideways oscillations in the bridge, which, in turn, caused people to sway more in step. These amplified oscillations only reinforced the swaying, causing the extreme sideways movement that pedestrians experienced.
The Cleveland Bridge solution
One of the main obstacles to solving this issue was finding a way to modify the Millennium Bridge, without compromising the structure’s already popular aesthetic.
In response, Cleveland Bridge Group partnered with Ove Arup & Partners to design and fit a dampener system that would both stay out of sight and make the structure more secure.
Fundamentally, these dampeners would function much in the same way as car shock absorbers; reducing the magnitude of the oscillations by turning that kinetic energy into heat energy, which is then dissipated through hydraulic fluids.
Jim Mawson, Head of Operational Delivery at Cleveland Bridge UK, describes the substantial scope of this method, “To reduce the sideways movement and vibrations of a 350-metre bridge, copious amounts of dampeners would be required. For the Millennium Bridge, we constructed a total of 91 dampeners, all designed to be installed seamlessly onto the structure’s aesthetic.”
In February 2002, almost two years after its initial opening, the Millennium Bridge was successfully reopened to the public.
Our dampening system upgraded the bridge’s capacity substantially, allowing for up to 5,000 people to cross at any one time – which is more than double the footfall that caused the initial swaying. What’s more, our rehabilitation work did not compromise the bridge’s design, which is now an iconic London landmark.
Chris Droogan, Managing Director for Cleveland Bridge Group, states “these types of innovative solutions are part and parcel of our every-day operations and skillset. We always strive to go above and beyond with our projects, providing leadership to the industry for bridge rehabilitation.”