Seismic Hazard Assessment of Oregon Highways

Considerable earthquake threat has been identified in the Western part of the continent and also more recently in many other regions across the nation. The effects of an earthquake can result in potential sudden detrimental impact on the transportation infrastructure where bridges represent vulnerability points within the network. When bridge damage occurs during a seismic event, short-term or long-term interruptions to traffic flow result. The economic impact of bridge damage includes not only the cost of structural repair, but also longer term consequences relating to valued loss of time when commuter and freight travel slows down to navigate the disrupted…

Considerable earthquake threat has been identified in the Western part of the continent and also more recently in many other regions across the nation. The effects of an earthquake can result in potential sudden detrimental impact on the transportation infrastructure where bridges represent vulnerability points within the network. When bridge damage occurs during a seismic event, short-term or long-term interruptions to traffic flow result.  The economic impact of bridge damage includes not only the cost of structural repair, but also longer term consequences relating to valued loss of time when commuter and freight travel slows down to navigate the disrupted network. Road and bridge owners need tools to assess the potential impact of the seismic hazard on their aging network.

In an effort to quantify the seismic risk for Oregon, Portland State University in collaboration with the Oregon Department of Transportation aims to develop a seismic risk assessment model along the major truck routes and include state owned bridges. The study had adopted a recently released FHWA developed software tool Risk for Earthquake Damage to Roadway Systems (REDARS2). The progress has been successful in collecting and combining available data from transportation, geotechnical and structural fields into a common database and in conducting preliminary analyses. The use of risk assessment methodologies by Oregon is some of the first application outside of the trial cases implemented by the REDARS2 development team. The study area of the Western part of Oregon represents the largest model, as measured by the geographical area as well as the number of bridges considered. Oregon has shown to be the trailblazer in adoption of this potentially powerful seismic hazard tool with other states considering similar efforts; PI is aware of New York and Utah states.

A number of limitations in the existing data as well as the software capabilities itself had been identified to the point that without further research and implementation, the results of the existing model are not realistic. The objective of this proposed research is to address the major limitations for the current state of the model to more appropriately represent the traffic conditions and the seismicity of the Pacific Northwest. These are necessary to more appropriately study the region and investigate the sensitivity of key input parameters such as bridge damage threshold and liquefaction threshold on the global results. The model will then be used to analyze the network resulting in recommendations toward bridge retrofit strategies.

OTREC theme of “healthy communities” reflects closely the topic and potential impact of this research by addressing transportation management along with safety. The research also addresses “the development and implementation of bridge management systems” along with “safety assurance of highway structures for extreme events” as identified in Highway Research and Technology: The need for Greater Investment (2002). Cross-discipline collaboration is necessary to conduct this work given the multi-disciplinary nature of the problem. Experts from the transportation planning and earthquake bridge engineering at Portland State University will be collaborating on this work.