Aurora Avenue Bridge Seismic Retrofit Study
Seattle, Washington
As a subconsultant, PanGEO assisted the Washington State Department of Transportation (WSDOT) in analyzing the feasibility of using friction-pendulum isolation bearings as a cost-effective retrofit alternative to protect the bridge from extensive damage in a seismic event. Currently there are only two major bridges in the world that use this technology for improving seismic performance, and the Aurora Avenue Bridge is the first WSDOT bridge proposed to use this technology. In addition to the Aurora Avenue Bridge analysis, one of the project goals is to use the outcome of this project to establish seismic design standards and policies for future retrofits of WSDOT bridges.
As the geotechnical engineer for the project, PanGEO provided design ground motion time histories using both probabilistic and deterministic approaches. The current WSDOT (500-year return interval), CalTrans (1000 year) and UBC (1000 year) criteria, as well as the 2000 IBC (2,500 year) design requirements were utilized in the probabilistic approach to develop design ground motions. Geotechnical and topographical factors that could impact the design ground motions were considered in our evaluation, including the depth to bedrock, Seattle Fault, existing fill adjacent to columns, soil liquefaction, and non-linear dynamic soil properties. In addition, PanGEO was responsible for providing soil stiffness parameters to separate bridge structural engineering firms, including T.Y. Lin and Imbsen and Associates, Inc. for their use in completing non-linear, dynamic analyses of the bridge to evaluate the feasibility of using friction pendulum bearings to reduce the seismic demands upon the bridge