Thermal track buckling is probably the major problem due to the advent of continuous welded rail track. In fact, when the rails temperature rises over a critical value, the track can buckle, suddenly or progressively, in the lateral plane. Both poor ballast conditions and large lateral alignment defects are the principal causes of such phenomenon. In a previous paper, a parametric finite element model for thermal track buckling simulation was presented and validated by comparison with analytical results of the literature. In this study, the finite element model has been further validated by comparison with analytical and numerical results obtained by three other authors. Moreover, to take into account the effect on the buckling temperatures of the vertical loads due to train passes, the tie-ballast lateral resistance has been modified along the track, taking into account the vertical reaction forces distribution induced by axle loads. A sensitivity analysis has been carried out both for tangent and curved track, considering two values of the alignment defect amplitude, and different values of the parameters that characterize actual railway vehicles. It is found that the conditions to trigger progressive buckling (△ T max ≈ △ T min ) are attained with small values of the truck center distance, and in a more accentuated manner in the presence of high values of the lateral alignment defect. △ T max and △ T min increase with axle spacing, and this increase is more pronounced for low values of the truck center spacing. △ T max and △ T min also increase with curve radius, but decrease for increasing values of the misalignment defect amplitude. In explosive buckling conditions (△ T max ≠ △ T min ), there is a limit value of the truck center distance above which the vertical load has no more effects, and the results of the static thermal buckling are found.

The mission of the U.S. Transportation Security Administration (TSA) is protection of the nation’s transportation systems to ensure freedom of movement for people and commerce. In furtherance of its mission, TSA’s Office of Security Capabilities has contracted with Transportation Technology Center, Inc. (TTCI) and Arup North America Ltd (Arup) to conduct research to quantify the vulnerability of railcars and infrastructure to damage caused by the use of explosives. The main objectives of the ongoing research program are to develop tools to evaluate the performance of existing railcar structures, develop potential mitigation measures for current railcars, and investigate future advanced designs under blast conditions. TTCI performed a series of full-scale tests on three major passenger railcar types: light rail, commuter and transit. Test scenarios were developed based on extensive risk assessment and historical data. Tested scenarios include single internal charges in various locations, simultaneous internal charges and external charges on a station platform. Well instrumented tests provide experimental assessments of existing railcars’ blast performance and data for validation and refinements of finite element blast models developed by Arup. The blast models incorporate sophisticated computational fluid dynamics (CFD) modeling of blast events to predict blast wave propagation and pressure applied on the structure. Hitherto research has focused on the railcar structure. However the test series has provided information on damage to infrastructure, including rail, ties, ballast, and both catenary and third-rail electrification systems. The finite-element blast models will provide railcar designers the means to investigate the effects of blast mitigation measures and reduce the need for physical tests. Several mitigation measures were installed and tested to evaluate their effectiveness. One car was equipped with typical interior components including seats and partition walls. One side of the car was equipped with standard components and the other side with remedial components that are intended to mitigate the effects of a blast. A similar approach was used for windows. This configuration allowed direct comparisons and performance assessments of the blast mitigation measures. Companion modeling and finite element analysis (FEA) of the blast response of the railcar and interior components provided a computational tool by which mitigation measures may be assessed and refined. This paper summarizes recent research sponsored by TSA and conducted by TTCI and Arup on blast vulnerability of railcars and infrastructure to damage caused by the use of explosives.

Flammable materials such as gasoline, ethanol, and diesel fuel are commonly transported in bulk via rail. In many cases, pockets of vapor can be generated inside the tank that can present a hazard if spilled during a collision or other catastrophic accident. Vapor conditions above the Lower Explosive Limit (LEL) if exposed to an external ignition source can result in an explosion or fire. Alternately, residual vapors within a tank present an explosion hazard if not properly vented or inerted prior to maintenance activities. This paper summarizes a generalized study of hazards associated with flammable liquids using computation fluid dynamics (CFD) to predict vapor conditions within a tank or following a spill. The analysis was verified in laboratory testing using scaled tank geometries. A demonstration case was developed using diesel fuel in a locomotive fuel tank. Typical road locomotives carry 3000–5000 gal of diesel fuel during normal operation. As the locomotive consumes fuel, large volumes are available for vapor generation within the tank. In a post-collision scenario, under ambient temperatures over the flash point of the fuel, the vapor that vents to the atmosphere presents a significant fire hazard. Further, flammable mists can be generated by the sprays that develop due to fuel leaks from a moving train. Studies of accident cases over a 10 year period indicated that a fire occurred in 80% of the accidents in which fuel was spilled. A CFD analysis was applied to the geometry associated with a locomotive fuel tank. The analysis models the two phase flow using the “volume of fluid” formalism in Fluent, and using a user defined diesel fuel evaporation algorithm. The tank and environmental parameters included fuel volume, fuel temperature, and air flow within the tank, and critical values of vapor content, temperature and velocity were plotted. The analysis predicted ignition of the external vapor cloud at temperatures relevant to a spill in a summer environment in the southwest, and propagation of the flame into the fuel tank. Laboratory testing confirmed the analysis: Once ignited, a flame propagated into the tank, causing an explosion and fire. The analysis methods developed can be applied to a variety of geometries and fluids, providing a basis for full scale testing. The overall intent of the analysis is to aid in the development of fire mitigation approaches for fuel and flammable material transport that would be practical for railroad use.