This seismic retrofit involved the main channel crossing section of the Dumbarton Bridge. Work included structural concrete overlay at 14 existing pier footings, structural concrete improvements to 16 existing pier caps, 16 structural steel jacking frames within the existing steel box girders, six friction pendulum bearings installed at each pier, replacement of two existing seismic joints, and the retrofit of two existing hinge joints. Shimmick added the improvements at both approach trestle structures by installing 28 steel pipe piles, each approximately 75 feet long and 4 feet in diameter. The piles were connected to the existing structure with structural concrete trestles.
Additional work included drainage improvements by installing a new pumping plant, 2,000 feet of 36-inch drainage pipe, and 2,000 feet of sheet pile cut-off wall, removing existing cathodic protection systems, improvements to the existing seismic monitoring electrical systems, miscellaneous electrical and fiber optic cable work, and removal of 2,200 lineal feet of the original Dumbarton Bridge (Ravenswood Pier).
Shimmick implemented an innovative approach in performing the work by using suspended work platforms to access the piers in lieu of accessing the work with marine equipment and temporary work trestles as depicted within the contract plans. This approach reduced the cost of the work to Caltrans, and it significantly reduced the environmental impact to the San Francisco Bay by eliminating the need to construct and then remove the as-planned temporary trestles. Despite limited construction access, the team focused on creating safe and efficient access for all of the work, both for the jacking frames and the existing pier footings overlay. Through innovative construction phase design, the team could limit the marine work and minimize the heavy lifting required within the bridge.
These access considerations allowed the material and personnel to safely, efficiently, and effectively access and perform the work. Shimmick also engineered an innovative platform design to eliminate access to the bridge’s underside from the waterside.
AGC of California recognized the Dumbarton Bridge Seismic Retrofit project with the prestigious AGC Constructor Award for Excellence in Partnering.
Shimmick helped foster a partnering atmosphere on the project by establishing an effective conflict resolution ladder with the Department. They would consistently offer engineered solutions to construction conflicts when encountered as opposed to identifying the conflict and placing the burden entirely on the Department to resolve. As a team, we were able to work through many difficult problems including modifying the jacking sequences for raising the bridge…a particularly sensitive matter for the Department.