When the Loma Prieta earthquake collapsed a section of the San Francisco-Oakland Bay Bridge 24 years ago—a portion of the upper deck buckled, killing one person—California officials deemed the eastern span of the 1936 steel-cantilevered truss bridge seismically unsound. The route is sandwiched between the Hayward Fault to the east and the San Andreas Fault to the west. A new bridge connecting San Francisco and the East Bay was necessary. After 11 years of construction and several major traffic closures, the new ten-lane eastern stretch of the bridge opened on Labor Day.
In 1998, state officials put together a panel to vote on the best design option to replace the 2.2 mile damaged eastern portion of Interstate 80 running from Yerba Buena Island to Oakland. Forgoing a basic solution, the majority voted in favor of a self-anchored suspension bridge, designed by San Franciscobased Donald MacDonald Architects and New York engineering firm Weidlinger Associates. The winning concept prominently features a single 525-foot-tall tower—the design element in which architect Donald MacDonald takes most pride.
"We slightly tapered the shafts of the tower so as to appear parallel to one another in the approach, and to keep a rhythm and lightness," said MacDonald. A pentagon theme was woven throughout, in the legs of the towers and the piers below, he said.
"The bridge is white, inspired by Oakland's container cranes", explained MacDonald, adding, "cities and bridges can brand themselves through color." The Golden Gate Bridge, cloaked in orange, comes to mind.
The new eastern span is actually comprised of two structural systems: a 1.2 mile concrete skyway and the suspension bridge, with its single loop cable system and tower. The side-by-side decks each contain five lanes flanked by shoulders. There is a temporary pedestrian and bike path on the right side of the eastbound roadway.
Engineering firms T.Y. Lin International Group and Moffatt & Nichol Engineers were hired to make MacDonald’s and Weidlinger’s vision a reality. To make the design seismically safe, the bridge would have to ride an earthquake like a wave. The design of the tower required four steel shafts bound together with shear-link beams capable of absorbing the energy of an earthquake. Hinge-pipe beams allow sections of the bridge to expand and contort. The skyway is supported by 160 concrete-battered piles, replacing the timbered piles of the original eastern span.
Light poles installed with more than 48,000 LEDs line the bridge, requiring about 50 percent less energy than the original section. The LEDs have a longer lifespan of 10 to 15 years, and are angled to prevent glare and minimize light pollution.
The project was not without its challenges. Originally estimated to take four years to build at a cost of $1.6 billion, the bridge became one of the most expensive projects in the state as the price of steel and concrete rapidly rose, mostly due to the building boom in China. In the end, the bridge has come in at $6.4 billion, with cost overruns funded by a 2007 $1 toll increase and state gas tax dollars.
The bridge may be open, but the work is not finished yet. Broken anchor bolts in the seismic stabilizers that were temporarily repaired with concrete saddles will get a final repair by this December. It will take nine months to remove most of the original eastern span and up to three years to completely demolish the outdated structure. Some portions will be kept, others will be recycled or sold for scrap.
After the original eastern span is removed, construction crews will permanently install a bike and pedestrian path, extending it to Yerba Buena Island. They will also replace a temporary ramp connecting the island to the eastern span. Both projects will be completed in 2015.