bridges

Building a Bridge in One Day

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Boston may be known for the abomination that was The Big Dig, but an incredible recent development is surfacing in the city: new bridges are being built in just a day or two! The New York Times reports on the phenomenon known as “accelerated bridge construction”:

Nowhere have the various techniques for speeding bridge work been more enthusiastically embraced than in Massachusetts, which replaced 14 bridges on Interstate 93 last year over 10 weekends. But similar techniques are being used around the country, from Mesquite, Nev., to the Golden Gate Bridge in San Francisco, which is getting 300 feet of new roadway one 25-foot prefabricated section at a time, 78 pieces in all. “We have a bridge that we simply cannot close to traffic,” said Ewa Bauer, chief engineer for the Golden Gate Bridge Highway and Transportation District.

Now, if only we could be as fast as the Chinese in building other things…

A Replacement Bridge in San Francisco

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There is a strong likelihood of a large earthquake in the San Francisco Bay Area — about a 2-in-3 chance of magnitude 6.7 or larger before 2036, according to the United States Geological Survey. This New York Times piece discusses the building of the new Bay Bridge:

Unlike more conventional suspension bridges, in which parallel cables are slung over towers and anchored at both ends in rock or concrete, the 2,047-foot suspension bridge has only a single tower and a single cable that is anchored to the road deck itself, looping from the eastern end to the western end and back again. (With a conventional design it would have been extremely difficult to create an anchorage on the eastern end, in the middle of the bay.)

The new bridge is the longest self-anchored suspension bridge in the world, and it is asymmetrical, with one side of the span longer than the other. The choice of such a design raised the cost of the project significantly. In a conventional suspension bridge, the road deck is added last, hung from suspender cables attached to the main cables. In a self-anchored design, the deck has to be built first.

The eastern span replacement of the San Francisco – Oakland Bay Bridge has been under construction since 2002. Originally scheduled to open in 2007, it is now scheduled to open to traffic in 2013 at an estimated cost of $6.3 billion. A good interactive from the NYT is here. An incredibly detailed Wikipedia article is here.