Bay Bridge Retrofit to Cost $250 Million
For more than 50 years, the double-deck San Francisco-Oakland Bay Bridge was a celebrated monument of structural engineering--a testament that even without computers or modern testing equipment, engineering wit and instincts could fashion steel-and-concrete spans that would endure.
Then came Oct. 17, 1989, when the 7.1 Loma Prieta earthquake caused a 50-foot upper-deck segment to collapse, killing one motorist. A 15-foot-long segment at the easternmost end of the bridge came within half an inch of falling, and other parts moved less dramatically.
The bridge was repaired and reopened a month later, but retrofitting and strengthening it to withstand a much larger quake will cost $250 million. That amounts to about 40% of the $650 million that would be set aside for toll bridges if voters approve a proposed $2 billion state bond measure in June.
The next most expensive retrofitting job is set for the Richmond-San Rafael Bridge and would cost $125 million.
By contrast, retrofitting Southern California’s two toll bridges is expected to cost far less: an estimated $32 million for the Vincent Thomas Bridge in San Pedro and $42 million for the San Diego-Coronado Bridge.
The other toll bridges needing strengthening are the San Mateo-Hayward, $95 million; Carquinez, $35 million, and Benicia-Martinez, $55 million. Those estimates add up to $634 million, but the total is expected to increase.
To make the Bay Bridge safe to reopen in 1989, the deck sections had to be jacked back into place, secured with restraining cables and reconnected with bigger bolts.
“Of course, that was not fixed for a big earthquake; it was just fixed to let the traffic go,” Berkeley civil engineering professor Abolhassan Astaneh said.
Astaneh headed a team of engineers and scientists that recommended retrofitting and strengthening the two-mile portion of the bridge between Oakland and Yerba Buena Island. The goal was to make the span strong enough to withstand 40 seconds of shaking from an 8.3 magnitude quake on the San Andreas Fault to the west of the bridge or a 7.3 magnitude quake on the Hayward Fault to the east.
Astaneh said about 10% to 15% of the $250 million cost of strengthening the Bay Bridge would be for the steel superstructure. The deck spans would be tied together more securely and deformable steel supports would be installed at the top of concrete columns to absorb some earthquake forces.
The rest of the money would pay for rebuilding the bridge’s piles and piers. Astaneh’s team recommended replacing the timber piles driven into the bay mud with 100-foot-long, concrete-filled steel pipes. The piers would also be wrapped in reinforced concrete.