Home >> Build It Bigger, Season 4, Episode 6: San Fran-Oakland Bay Bridge

Build It Bigger, Season 4, Episode 6: San Fran-Oakland Bay Bridge

by Danny Forster on May 21, 2010

San Francisco Oakland Bay Bridge
Episode 6 season 4
Bridges seem at first glance to be pure utility, as necessary and as boring as spoons. What could be simpler than a way to get across? Well, of course, it′s anything but simple, especially if you throw in a seismic threat of epic proportions, an absence of bedrock, and lots and lots of traffic. Those are the complicating factors of the Bay Bridge project.

The Bay Bridge is the third busiest bridge on the planet, delivering 270,000 cars a day between San Francisco and Oakland. Actually, it′s two bridges: the west span, which connects San Francisco to Treasure Island, and the east span, which continues from Treasure Island to Oakland. The west span is a beautiful suspension bridge, with elegant, swooping cables; the east span . . . not so beautiful. It′s your basic industrial truss bridge, and to San Franciscans, accustomed to the reflected glory of the Golden Gate, it′s not all that lovable.

It′s also not all that safe. In 1989, the 7.1 magnitude Loma Prieta earthquake broke a section of the upper deck and sent all 250 tons crashing to the roadbed below. They patched it up, but they knew they′d have to replace it before an even bigger earthquake hit. (When you live above the San Andreas Fault, you make every decision knowing the "even bigger" one is coming.)

So that was 20 years ago and they′re still working on the new bridge. That′s because it will be the single largest public works project in the history of California, running now to over six billion dollars. Why so time-consuming and so pricey? I′m glad you asked . . .

(1) On account of the lack of viable bedrock, they had to invent a completely new kind of bridge: a Self-Anchored Suspension Bridge, with a mile of cable suspended in an enormous loop from a single tower in the center. It′s flexible, it′s stable, and it looks cool—which is one of the stated aims of the state board that commissioned the design. They didn′t quite put it that way, but they insisted on having a "signature bridge," one that could hold its own visually within view of the Golden Gate.

(2) They have to defend against the next earthquake. This time they′re not even trying to build an infallible bridge; they assume that the bridge will fail in the next earthquake. The trick is to plan for that, to direct the failure in such a way that damage to the bridge is minimal. So they′re adding shock-absorbing steel beams as a "crumple zone" to deflect the force of the quake from the tower and the road.

And (3) they have to do all of this next to the existing bridge, without stopping traffic. Did I mention the 270,000 cars a day?

Meanwhile, there′s ongoing maintenance of the west span as well, which my producers used as an excuse to get me to change a bulb on the "string of pearls"—the lights that grace the cable and the bay at night. So yes, I walked the cable. Which produced a kind of quake-like effect in my legs. And no, nothing boring about bridges at all.
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