Seismic Vulnerability Assessment and Development of Analytical Fragility Curves for Railroads

In a highly seismic country like Iran, safety of lifeline systems is of utmost importance. Thus, in order to develop reliable systems that can withstand severe earthquakes, railroad tracks should be properly designed and maintained. A useful tool for the assessment of structures under earthquake is fragility curves. For railroad tracks, which are designed to withstand landslides, liquefaction, etc., i.e. disasters other than earthquakes, an empirical approach is used to establish fragility curves with specific values for critical deformations. An analytical approach provides an attractive alternative and is used here. In order to make a large number of required analyses possible, a macro-element is developed and used for modeling the track system. In this model, the ballast and subgrade are represented by nonlinear springs. Fragility curves presented here are for different types of ties and roadbed properties. The results indicate that lighter ties (wood) will result in much lower seismic forces in the system than heavy (concrete) ties.