MILLENNIUM BRIDGE MAP

MILLENNIUM BRIDGE MAP

The first horizontal suspension bridge is also the first to cross the Thames in over a century. Presiding over the pantheon of contemporary architects, Norman Foster (1935-), chairman and founder of Foster + Partners, has delivered a global collection of iconic buildings that expose their precise, often new technologies; encourage civic engagement; and aim to use as little energy as possible. There are few typologies that the Pritzker laureate has not explored; he’s conceived an artificial island airport in Hong Kong, the carbon-neutral city of Masdar, and a prototypical droneport to provide emergency supplies to remote African towns. In 1996, Foster teamed up with sculptor Sir Anthony Caro and engineering firm Arup in an international competition sponsored by the Financial Times to design a footbridge across the Thames River. The bridge was part of a national celebration of the new millennium. Two hundred teams from around the globe vied for the opportunity to design the crossing, the first in central London in more than a century. After the submissions were whittled down to six groups of superstars in the fields of art, architecture, and engineering (see here), Foster and friends emerged as the winners.

The competition guidelines presented a bit of a quandary. On one hand, the bridge had to epitomize innovation, but on the other, it had to have a minimal profile to maintain the historic riverbank views. At the time, Foster said his team wanted to push suspension techniques “as far as possible” and make “an absolute statement of our capabilities at the beginning of the 21st century.” Spanning 1,050 feet (320 meters), the shallow suspension bridge utilizes cables that are placed horizontally, instead of vertically, as in more conventional suspended spans.

FOSTER + PARTNERS

Two robust Y-shaped piers support the eight cables that run along the sides of the 13-foot (4.0-meter)-wide aluminum deck, which is carried by a series of steel transverse arms that clamp onto the cables at 26-foot (7.9-meter) intervals. The cables never rise more than 7.5 feet (2.3 meters) above the deck, opening up panoramic views of the river and preserving sightlines from the buildings on either riverbank. Lighting engineer Claude Engle created the lighting scheme, which transforms the rugged steel structure into a slender arc at night.

When the Millennium Bridge opened on the heels of the Tate Modern, a cavernous industrial building that was converted into a contemporary art museum, it breathed new life into Southwark and enlivened the staid north embankment, anchored by Sir Christopher Wren’s noble dome at St. Paul’s Cathedral. The bridge proved so popular on its opening weekend, however, that it was closed for almost two years. The culprit? Synchronous lateral excitation, a little-known phenomenon that occurred when the crowd’s footfalls caused small but constant stresses. No one could have predicted what happened next. According to Foster biographer Deyan Sudjic, “All 690 tons of steel-and-aluminum deck began to sway left and right like a giant executive desktop toy, so much so that pedestrians, suspended above the Thames on slender steel cables, began to clutch at handrails to steady themselves, throwing their weight against the sway in an effort to stay upright.”

Norman Foster’s conceptual sketch emphasizes the bridge’s vital, axial relationship with St. Paul’s Cathedral (1711).

An astonishing 160,000 people crossed the bridge during its opening weekend, far more than the structure could handle.

Arup mitigated the wobble by adding multiple dampers beneath the deck, a solution that did not compromise the bridge’s appearance and resulted in changes to bridge-building codes globally. Millions cross the beloved city landmark each year. The bridge has enlivened both sides of the Thames, connecting the Tate Modern (2000) and the venerable St. Paul’s. Drivers cross on a roadway that is 187 feet (57 meters) above the sea. Four planes of cable stays fan out from the 668-foot (204-meter)-tall pylons. Only the pylons were cast in situ; the remaining bridge components were built on land and towed out to the alignment.