Journey to the Center of the Bay Bridge

West
Thursday, July 1, 2010
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Access to the inside of the new Bay Bridge skyway is via catwalks suspended over the water.

Action-movie directors: Consider shooting your next film in the innards of one of the biggest projects going up in the Bay Area: the new, $6 billion eastern span of the Bay Bridge.  There’s the evident glamour of a self-anchored suspension bridge–the Calatrava-esque part with the tower and cables holding everything up, which is still yet to be built. But already in place is the 1.2-mile  “skyway” portion, and inside the concrete monolith are whole rooms, including an electrical substation, and a tunnel that runs the length of the skyway.  Only maintenance crews are typically allowed in this secret warren, but a media tour led by a Caltrans representative provided a close-up of some of its more unusual features.

A trip under the eastbound lane.

A portion of the existing Bay Bridge collapsed in the 1989 Loma Prieta earthquake. In anticipation of the next major earthquake, the new bridge has five expansion joints with shock absorbers, cushioning the impact. Hinge beams, which are enormous steel dowels inserted into the joints, allow compression of the bridge sections but counter shear forces.

The end of one of the hinge beams, which will allow the bridge segments to move during an earthquake.

Even before the formal EIR process, the design team was mindful of the wildlife that would be affected. The amount of force that is necessary to drive piles 300 feet deep into the Bay mud and create the footings for the bridge is also enough to kill fish, so the team developed a “bubble curtain” system to diffuse the impact.  Another feature is a nod to the local bird population. The smooth concrete of the new bridge doesn’t provide the roosting platform of the current bridge’s Erector-set trusses, so the new bridge offers special “cormorant condos.”

On the underside of the skyway, wire-mesh ledges function as "cormorant condos."

So while the hard-won, pricey suspension span will be a thing of elegance, the other part ain’t no slouch either.

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