OPAC Consulting Engineers

San Francisco - Oakland West Bay Crossing

San Francisco - Oakland, California


California Department of Transportation (Caltrans)
Brian Maroney
email: brian_maroney @dot.ca.gov


Study completed 1994

Scope of work:

Seismic Evaluation

Construction cost:


Services Performed:

  • Criteria development
  • Foundation modeling
  • Local capacity modeling
  • Response analysis
  • Vulnerability evaluation
  • Retrofit concepts


  • Nonlinear seismic analysis
  • Seismic vulnerability and retrofit criteria
  • Multi-support dynamic analysis
  • Coordination of multiple subconsultants

The two-mile-long West Bay Crossing of the San Francisco - Oakland Bay Bridge carries Interstate Highway 80 across San Francisco Bay. OPAC evaluated the tandem suspension bridge for Caltrans to determine its anticipated seismic performance in a major earthquake, and to make recommendations and cost estimates for seismic retrofit measures. The scope of work included the following components:

  • Criteria development. Establishment of load and deformation criteria for determining vulnerability.
  • Foundation modeling. Soil-Structure Interaction modeling to determine properties and demands.
  • Global demand modeling. Dynamic 3-D modeling to capture global and regional inelastic response.
  • Local capacity modeling. Computer and manual evaluation of load and deformation capacities.
  • Response analysis. Response spectrum and multi-support time history, linear and nonlinear analyses.
  • Vulnerability evaluation. Estimation of vulnerability based on capacities, demands, and behavior.
  • Retrofit concepts. Identification of retrofit strategy to achieve a higher performance standard.

Final design of retrofit measures was performed by Caltrans, using most elements of the retrofit strategy identified in this evaluation. Retrofit construction was completed in 2004.