Evaluation of seismic damage to bridges and highway systems in Shelby County, Tennessee

Past earthquakes have demonstrated that bridges are one of the most vulnerable components of highway transportation systems. In addition to bridges, roadways may also be subject to damage, particularly in an area prone to earthquake-induced liquefaction. As a consequence, the highway transportation systems after an earthquake might be impaired and the post-earthquake emergency response might be compromised. Furthermore, the impact on the regional economy might be very significant from the damage to highway systems. Since highway transportation systems are critical lifelines for people living in an urban area, it is important to evaluate the vulnerability of bridges and highway systems in earthquake-prone regions.; Memphis and Shelby County, Tennessee are located close to the southwestern segment of the New Madrid seismic zone (NMSZ). This zone produced three of the largest earthquakes in North America in 1811--1812. Presently, the NMSZ is still active and is considered by engineers, seismologists, and public officials as the most hazardous seismic zone in the central and eastern United States. Bridges in the Memphis area were generally not designed for seismic resistance until 1990. Therefore, the majority of existing bridges might suffer damage from earthquakes occurring in the NMSZ.; The overall objective of this study is to evaluate the expected damage to bridges and roadways on the major routes in Memphis and Shelby County resulting from New Madrid earthquakes with the aid of geographic information system (GIS) technology. The road network selected for this study includes all the Interstate highway system, all the primary and secondary routes maintained by the state, and most of the major arterial routes. There are 452 bridges on the selected roadway systems and data pertinent to these bridges and roadway systems were collected and implemented as a GIS database.; The bridges in the Memphis area were classified into several types and damage states were determined by the Capacity/Demand (C/D) ratios of bridge components. The damage states considered in this study are no/minor damage, repairable damage, and significant damage. The seismic fragility analysis of each bridge classification was performed and the results were expressed as fragility curves. In this study, eight bridge classifications were defined and a fragility curve was developed for each.; To estimate the seismic hazard, three scenario earthquakes located at Marked Tree, Arkansas was established for this study. The moment magnitude of the M scenario earthquake was set as 6.5, 7.0, and 7.5 to represent various sizes of earthquakes that might occur in the NMSZ. For each scenario earthquake, the intensity of ground shaking and liquefaction-induced permanent ground deformation in Shelby County were estimated, and then the expected damage to bridges and roadway systems was determined. The results from this study can be used to prioritize bridges for retrofitting, to prepare a pre-earthquake preparedness plan, and to develop a post-earthquake emergency response plan. Furthermore, the results can also be used to assess the regional economic impact from the damage to highway transportation systems.