Gallery: How to Build an Earthquake-Resistant Bridge

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Few engineering projects have the scope, costs or risks involved in building a new bridge.

San Francisco Bay Area residents got a peek at what’s involved Wednesday, when builders set in place the first segment of a tower that will soon hold up a brand-new span of the San Francisco Bay Bridge.

Wired captured photos of the event, as well as many inside photos of the new bridge that we shot on a recent tour of the massive construction project.

More than 250,000 vehicles pass over this bridge every day, carrying people and freight between San Francisco and the east side of the bay. You can’t exactly ask that much traffic to wait patiently while you tear down the existing bridge and replace it with a new one.

Complicating matters is the fact that the San Francisco Bay Area is one of the most seismically active regions of the United States. Any bridge built here has to be able to withstand a massive quake — since some big shaker is almost certain to hit sometime during the bridge’s expected 150-year lifespan.

In fact, engineers are designing the new Bay Bridge segments to withstand the largest earth movements predicted for the next 1,500 years. The specifications call for the bridge to be open to traffic within hours after such a massive quake, with minimal repairs required.

No wonder it has taken two decades to come up with a replacement for the Bay Bridge’s damaged eastern span.

This page: What locals call the Bay Bridge is actually three bridges: a pair of suspension bridges leading from San Francisco in the west to Yerba Buena island in the middle of San Francisco Bay; and an eastern section made out of steel girders, leading from the island to Oakland, on the east side of the bay. Connecting the two is a 76-foot wide, 58-foot high tunnel — the largest bore tunnel in the world — going through the heart of the island.

It’s the eastern span, shown here, that took a hit during the 1989 Loma Prieta earthquake. A section of the upper roadway collapsed in that quake.

Photo: Stefan Armijo/Wired.com