Purpose

The United States Federal Highway Administration (FHWA) is sponsoring a six-year research project titled "Seismic Vulnerability of Existing Highway Construction", which is being carried out by the Multidisciplinary Center for Earthquake Engineering Research (MCEER). A major task under this project is to develop an advanced procedure for seismic risk analysis (SRA) of highway-roadway systems. This paper summarizes the SRA procedure that has been developed, including (a) recent enhancements; (b) an application of the procedure to the Memphis, Tennessee highway–roadway system; (c) and future research directions to further develop the procedure.

Outcome

The SRA procedure can be carried out for any number of scenario earthquakes and simulations, in which a "simulation" is defined as a complete set of system SRA results for one particular set of input parameters and model uncertainty parameters (which differ between simulations because of random and systematic uncertainties). For each earthquake and simulation, the SRA procedure uses geoseismic, geotechnical, structural, transportation, and economic models to estimate: (a) earthquake effects on system-wide traffic flows (e.g., travel times, paths, and distances); (b) economic impacts of highway system damage (e.g., repair costs and costs of travel time delays); and (c) post-earthquake traffic flows along vital roadways (to facilitate emergency response planning). The heart of the SRA procedure is a GIS data base comprised of four modules that contain the data and models needed to fully characterize the system, hazards, component vulnerabilities, and economic impacts of system damage. Features of the procedure include: (a) its GIS framework, which enhances data management, analysis efficiency, and display of analysis results; (b) its modular GIS data base, which facilitates the incorporation of improved models from future research efforts; (c) its ability to develop SRA results that are either deterministic or probabilistic, thereby facilitating its usefulness for a variety of applications; and (d) its use of rapid analysis procedures, to enhance its future use as a real-time predictor of system performance after an actual earthquake.

New developments in the procedure include: (a) consideration of multiple scenario earthquakes based on an adaptation of models from the USGS National Hazards Mapping Program, within the framework of a "walk-through" evaluation procedure; (b) updated models for estimating system-wide ground motion and liquefaction hazards; (c) improved traffic-state fragility models for bridge and roadway components, that estimate the probability of occurrence of a given traffic state (defined as the number of lanes that remain open to traffic at various times after an earthquake) as a function of the level of ground shaking and permanent ground displacement at the site of the component; and (d) an Associative Memory transportation network analysis procedure that provides rapid and technically sound estimates of post-earthquake traffic flows.

Conclusions

Current practice in the United States for prioritizing bridges and other components for seismic retrofit and for establishing their seismic design and retrofit criteria does not consider the importance of the component to post-earthquake traffic flows within the highway-roadway system. The SRA procedure developed under this program provides a rational and efficient method for bringing system traffic-flow considerations into such engineering applications, and also into planning for system enhancement and for post-earthquake emergency response.

¹Principal, Seismic Systems & Engineering Consultants, 8601 Skyline Boulevard, Oakland CA 94611.
²President, Natural Hazards Management Inc., Torrance CA.
³Associate Professor of Civil Engineering, University of Southern California, Los Angeles CA
⁴GIS Analyst, City of San Jose, San Jose, California.

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