Millenium Bridge

Londoners quickly dubbed the Millennium Bridge the “Wobbly Bridge” after its alarming swaying motion on opening day in June 2000. Only two days later, the bridge was closed for repairs and remained shut for almost two years while engineers worked to fix the issue. The bridge between Southwark Bridge and Blackfriars Railway Bridge reopened in February 2002, having been stabilised.

The Millennium Bridge connects St. Paul’s Cathedral on the north bank of the Thames with the Globe Theatre, Bankside Gallery, and Tate Modern on the south. Its sleek design resulted from a 1996 competition organised by Southwark Council and RIBA. The winning proposal came from Arup Group, Foster and Partners, and artist Sir Anthony Caro, who envisioned a “blade of light” that used supporting cables hidden below the deck for a minimal profile. The bridge’s aluminium deck stretches 325 meters (1,066 ft) long and 4 meters (13 ft) wide, supported by eight cables tensioned to pull against piers at each bank with a force of 2,000 tons. This design could handle up to 5,000 people at once.

Construction began in 1999 and was completed in June 2000, though the bridge opened a month late and £2.2 million over budget, bringing the total cost to £18.2 million. The launch attracted huge crowds, with 90,000 people crossing the bridge on its first day. But the excitement quickly turned to concern when the bridge began to sway, prompting an immediate closure. Engineers discovered the phenomenon responsible was called “synchronous lateral excitation,” a rare occurrence where pedestrians, reacting to the bridge’s slight sway, unintentionally synchronised their steps, amplifying the motion.

Unlike vertical vibrations (well understood in bridge design), lateral vibrations hadn’t been thoroughly studied. The bridge swayed about 70 millimetres (2.8 inches) as pedestrians unconsciously adjusted their steps in sync with the motion, creating a feedback loop. While limiting the number of people crossing the bridge didn’t stop the sway, engineers from Arup studied the problem using platforms at the University of Southampton and Imperial College London.

The solution was to install 37 viscous dampers—17 chevron-shaped dampers under the deck to reduce lateral movement, four vertical dampers to control both lateral and vertical shifts, and 16 pier dampers to manage lateral and torsional forces. Additionally, 52 tuned mass dampers were added to minimise vertical motion. The retrofit, costing £5 million, was completed between May 2001 and January 2002. After extensive testing, the bridge was successfully reopened and has since remained stable, though its “Wobbly Bridge” nickname stuck.

In 2006, artist Bill Fontana explored the bridge’s vibrations in his *Harmonic Bridge* exhibit at Tate Modern. By amplifying the higher-frequency resonances within the bridge’s cables, he created an immersive sound experience in the Turbine Hall, blending architecture, engineering, and art.

Today, the Millennium Bridge remains a popular Thames crossing, known for its modern design, stunning views of St. Paul’s Cathedral, and its wobble-free journey across the river.