Seismic Risk, Rating, and Assessment System for Bridges Along I-24 in Western Kentucky

Following a seismic event along the New Madrid Seismic Zone (NSMZ), I-24 in western Kentucky is considered a high priority and an emergency route for Kentucky and the states surrounding the NMSZ. It is essential that I-24 remains functional and operational following a major seismic event. This requires ensuring the ability of all the bridges along I-24 to withstand future major earthquakes. I-24 is only one of a number of priority routes in Kentucky, and due to the limited funds and personnel, it would not be feasible to assess the safety of each bridge with adequate details. The main objective of this study was to provide and apply a seismic risk, rating, and assessment system for 127 bridges and embankments on and over I-24. The evaluation system will result in identifying the most vulnerable bridges to damage during a major seismic event. Having identified all vulnerable bridges to seismic damage, more in-depth assessment can be carried out and retrofitting solutions can be recommended. Each bridge site along I-24 in western Kentucky was visually inspected and a comprehensive inventory of the bridges was compiled. The seismic rating system and detailed evaluation procedures for the bridges were presented. The 127 bridges were evaluated for the 50-year and the 250-year seismic events. Fourteen bridges were deemed susceptible to severe damage during future major earthquakes and were selected for subsequent detailed seismic evaluation. The detailed evaluation was based on the capacity/demand ratio method. Deficiencies of the seismic performance of the 14 bridges were documented, and retrofit recommendations were presented. The results indicate that the evaluation system provides an effective means to prioritize and recommend retrofit measures for highway bridges. Another objective of the study was to provide and apply a simple methodology to carry out a preliminary seismic vulnerability assessment of the 127 bridge embankment sites. A ranking methodology was developed and a priority list of the embankments with the highest seismic failure risk was generated. The priority list was prepared on a county-basis for the bridge embankments during the 50-year and the 250-year seismic events. The results of the study shall enable decision makers to take appropriate short term and future actions for those bridges and embankments with the highest seismic failure risk.