The bulk of the bridge inventory in Oregon was built prior to the current understanding of bridge response and prior to current understanding of the expected earthquake demands. While some bridges are being replaced due to other deficiencies, majority are expected to continue to stay in service for decades to come. Prioritization method is needed for deciding on bridge investment or for allocating the limited resources available. The overall goals of the research are to develop and apply a retrofit prioritization methodology that utilizes a statewide seismic risk assessment approach with data that are based on realistic bridge fragility for Oregon. A seismic risk model incorporating highway bridges within an interconnected statewide transportation network has been created at Portland State University, creating a unique opportunity to apply such retrofit methodology.
The model currently relies on nationally developed fragility relationships and does not include cases of retrofitted bridges, which are necessary in order to quantify the performance and monetary benefits of the retrofit on the transportation network. One of the common bridge types in Oregon are multi-span reinforced concrete continuous girder bridges with poorly confined rectangular cross section columns. Numerical analyses will be used to design two retrofit options based on a representative bridge. One of the measures will be selected and experimentally evaluated using large scale cyclic tests. The fragility will be obtained from non-linear analyses of numerical models of the representative bridge with component behavior calibrated to the experimental results. The fragility relationship will then be incorporated into the existing statewide seismic risk assessment model.
The updated statewide model will be used to implement the prioritization methodology for Oregon highway bridges by conducting parametric analyses of transportation system performance using existing earthquake scenarios. The retrofit methodology is envisioned to not concentrate on individual bridges, but instead evaluate the cost and benefit for highway segments or entire routes. New knowledge will be created in application of new technologies for seismic retrofit and in considering prioritization in the context of earthquake impacts on the transportation system. The outcomes of the research will have a direct local impact on transportation system management, while also having national relevance given the combination of a seismic exposure and aging bridge infrastructure nationwide.