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British Millennium Bridge Reopens After Safety Upgrades - 2002-02-24

It took a while longer to get it right and it cost $7 million more than anticipated, but London's new pedestrian bridge, dubbed the Millennium, has finally opened to the public.

Twenty months ago, London's first new bridge over the Thames River in more than a century opened with fanfare.

But there was a problem: it wobbled, and it wobbled badly. It shimmied and it shook. And after three days, it was closed as the engineers went back to the drawing board. Architect Lord Foster remembers. "Of course it has been an embarrassment," he said. "But as you know, it was a new phenomenon. It was something that the codes, the rules had never taken into account. But you have to remember, it was always safe."

Safe yes, but disconcerting nonetheless. The problem was described as something called "synchronous lateral excitation." Basically, when too many people walked over the bridge at one time, each footstep exerted a slight sideways force, which, in turn, caused a very noticeable wobble. The pedestrians then compensated by spreading their feet further apart, which increased the lateral push or movement.

The solution was fairly simple. Ninety-one giant shock absorbers installed underneath the sleek, 350-meter bridge connecting the Tate Modern museum on the south bank and St. Paul's Cathedral to the north have done the trick. It is steady, and crossing it now is no longer an adventure.