A study has been conducted of locomotive crashworthiness in a range of collision scenarios to support the efforts of the Locomotive Crashworthiness Working Group of the Federal Railroad Administration's Railroad Safety Advisory Committee (RSAC) to develop locomotive crashworthiness requirements. The RSAC is a government/industry committee including all segments of the rail community, with the purpose of developing solutions to safety regulatory issues. This paper presents the results of a study of the crashworthiness of conventional and modified locomotive designs in five collision scenarios. The five collision scenarios studied are:1. in-line collision of two locomotive-led trains with trailing locomotive overriding leading locomotive 2. in-line collision of two locomotive-led trains with one colliding locomotive overriding the other 3. locomotive grade crossing collision with highway vehicle hauling logs, with principal impact on locomotive window area 4. oblique collision, locomotive with intermodal trailer 5. oblique collision, locomotive with freight car
Concrete tie rail seat abrasion/deterioration (RSA) has been an issue since the inception of concrete ties. As a result of recent derailments involving abraded concrete ties on curved track, the Federal Railroad Administration set up a task force to study abrasion/deterioration mechanisms and develop automated detection methods using existing research vehicles. A portion of this study reviews historical development of concrete abrasion due to moisture or foreign materials incorporated under the rail seat that tend to abrade concrete ties evenly across the rail seat area. This report discusses a newly identified concrete tie deterioration mechanism characterized by material loss in a triangle toward the field side of the rail seat, resulting from wheel rail interaction involving track geometry variations.The NUCARS™ model was used to evaluate the vertical and lateral loading at one of the recent derailment sites using the track geometry measured approximately one month before the derailment. Wheel loads predicted from the model, based on P-42 Amtrak Locomotive, were used to evaluate the pressure distribution at the rail concrete tie interface and were compared with allowable design bearing pressure for concrete used in the manufacture of concrete ties. The results indicate that applied stress on the field side of a concrete tie due to outward rail roll can exceed the design values. Applied pressure distribution exceeding the design strength on the field side tends to abrade concrete ties in a triangular wear pattern that produces wide gage. Charts were developed to convert measured field side abrasion/deterioration to additional gage widening under an applied vertical load for identifying critical locations with wide gage defects. Further, techniques for field inspectors to detect, measure, and evaluate rail seat abrasion/deterioration (RSA) based on commonly used inspection technology are discussed.
Application of the Nadal Limit to the prediction of wheel climb derailment is presented along with the effect of pertinent geometric and material parameters.Conditions which contribute to this climb include wheelset angle of attack, contact angle, friction and saturation surface properties, and lateral and vertical wheel loads. The Nadal limit is accurate for high angle of attack conditions, as the wheelset rolls forward in quasi-static steady motion leading to a flange climbing scenario. A detailed study is made of the effect of flange contact forces F tan and N, the tangential friction force due to creep and the normal force, respectively. Both of these forces vary as a function of lateral load L. It is shown that until a critical value of L/V is reached, climb does not occur with increasing L since Ftan is saturated and the flange contact point slides down the rail. However, for a certain critical value of L/V (i.e. the Nadal limit) F tan is about to drop below its saturated value and flange climb (rolling without sliding) up the rail occurs. Additionally, an alternative explanation of climb is given based on a comparison of force resultants in track and contact coordinates.
Finite element models are developed for the railroad concrete crossties and are employed to analyze their center negative flexural responses to two center binding conditions: a center negative moment test condition and a hypothetical deteriorated ballast support condition. These conditions can lead to center negative flexural cracks and, eventually, sudden, catastrophic failure of the concrete ties when the loads reach critical magnitudes. When the concrete ties fail completely and consecutively in track, the gage can be sufficiently widened to cause derailment. The finite element results are first validated with the available test data, and the validated finite element models are then employed to obtain and evaluate the cracking/failure patterns and force-displacement characteristics of the concrete ties in the center negative flexural mode in static and dynamic analyses. The finite element analyses predict the critical wheel loads above which catastrophic tie failure is likely to occur, and the dynamic critical failure loads are shown to depend on the center binding ballast support conditions as well as the worn concrete tie conditions. The worn tie conditions that include bottom abrasion and prestress loss can significantly reduce the dynamic critical failure loads and, thereby, adversely affect the center negative flexural performance of the concrete ties.
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