Dumbarton next in line for retrofit 

While work to replace the eastern span of the Bay Bridge continues, Caltrans is preparing to make $220 million in seismic upgrades to another commuter span — the Dumbarton Bridge.

Construction is slated to begin next year on the retrofit of the 1.6-mile bridge, which connects Menlo Park on the Peninsula to Fremont in the East Bay.

The upgrade includes strengthening 36 water piers by adding concrete encasements on the footings and columns, replacing all
44 deck expansion joints and strengthening the two bridge deck hinges and deck section with added steel bracings, according to planning documents.

The project was approved by the San Francisco Bay Conservation and Development Commission, a state oversight agency, earlier this month.

The project is expected to start mid-2010 and take three years to complete, according to Caltrans spokesman Bob Haus.

While the majority of work will take place under the bridge, the job will require several weekend closures in order to raise the span roughly 5 inches and fit new pieces underneath the deck of the bridge.

“It won’t be five days like the Bay Bridge,” Haus said. “I don’t think they’ll need any long-term lane closures since most of the work is on the columns under the bridge.”

The Bay Bridge was closed for five days earlier this month for crews to install a temporary span near Yerba Buena Island in anticipation of work that will replace the 70-year-old stretch of roadway. It was the third Labor Day closure in four years.

The Dumbarton opened in October 1982. According to Bay Conservation and Development Commission documents, after the 1989 Loma Prieta earthquake, the state identified the Dumbarton Bridge as “part of the critical transportation system across the Bay.”

The bridge, however, does not meet current seismic standards and would be at risk if another magnitude 7.0 quake strikes the Bay Area, according to the project’s planning documents.

On the basis of research conducted since the Loma Prieta earthquake, the U.S. Geological Survey and other scientists concluded that there is a 70 percent possibility of at least one magnitude 6.7 or greater earthquake, “capable of causing widespread damage, striking the San Francisco Bay region before 2030, wrote Caltrans in its application to the BCDC.

Haus said the bridge improvements incorporate the latest technology resulting from ongoing study about seismic activity.

“You can always add more to your body of knowledge,” Haus said. “Every time there is seismic activity we learn something new. And every time there is something new to add to the safety of the bridges we will do that.”

In addition, Caltrans also plans to include about $3 million in other improvements around the bridge, including enhanced public access outlooks, resurfacing the existing parking lots and frontage roads on the bridge approaches, building a new bridge overlook and widening bike and pedestrian access, according to BCDC documents.

Bay Area toll bridges

  • Antioch Bridge
  • Benicia-Martinez Bridge
  • Carquinez Bridge
  • Dumbarton Bridge
  • Richmond-San Rafael Bridge
  • S.F.-Oakland Bay Bridge
  • San Mateo-Hayward Bridge

Source: Caltrans

 akoskey@sfexaminer.com

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