Brian Marquis

Prevention of derailments due to concrete tie rail seat deterioration

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 Nadal Limit for the Prediction of Wheel Climb Derailment

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 F(tan) 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)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. The effects of longitudinal creep force F(long) and angle of attack are also investigated. Using a saturated creep resultant based on both [F(tan), F(long)] produces a climb prediction L/V larger (less conservative) than the Nadal limit. Additionally, for smaller angle of attack the standard Nadal assumption of F(tan)=μN may lead to an overly conservative prediction for the onset of wheel climb. Finally, a useful analogy for investigating conditions for sliding and/or rolling of a wheelset is given from a study of a disk in rigid body mechanics.

Effect of the linearization of the kinematic equations in railroad vehicle system dynamics

The sensitivity of the wheel/rail contact problem to the approximations made in some of the creepage expressions is examined in this investigation. It is known that railroad vehicle models that employ kinematic linearization can predict, particularly at high speeds, significantly different dynamic response as compared to models that are based on fully nonlinear kinematic and dynamic equations. In order to analytically examine this problem and numerically quantify the effect of the approximations used in the linearized railroad vehicle models, the fully nonlinear kinematic and dynamic equations of a wheel set are presented. The linearized kinematic and dynamic equations used in some railroad vehicle models are obtained from the fully nonlinear model in order to shed light on the assumptions and approximations used in the linearized models. The assumptions of small angles that are often made in developing railroad vehicle models and their effect on the angular velocity, angular acceleration, and the inertia forces are investigated. The velocity creepage expressions that result from the use of the assumptions of small angles are obtained and compared with the fully nonlinear expressions. Newton-Euler equations for the wheel set are presented and their dependence on Euler angles and their time derivatives is discussed. The effect of the linearization assumptions on the form of Newton-Euler equations is examined. A suspended wheel set model is used as an example to obtain the numerical results required to quantify the effect of the linearization. The results obtained in this investigation show that linearization of the creepages can lead to significant errors in the values predicted for the longitudinal and tangential forces as well as the spin moment. There are also significant differences between the two models in the prediction of the lateral and vertical forces used to evaluate the L/V ratios as demonstrated by the results presented in this investigation.© 2005 ASME

Vehicle Track Interaction Safety Standards

Vehicle/Track Interaction (VTI) Safety Standards aim to reduce the risk of derailments and other accidents attributable to the dynamic interaction between moving vehicles and the track over which they operate. On March 13, 2013, the Federal Railroad Administration (FRA) published a final rule titled “Vehicle/Track Interaction Safety Standards; High-Speed and High Cant Deficiency Operations” which amended the Track Safety Standards (49 CFR Part213) and the Passenger Equipment Safety Standards (49 CFR Part 238) in order to promote VTI safety under a variety of conditions at speeds up to 220 mph. Among its main accomplishments, the final rule revises standards for track geometry and enhances qualification procedures for demonstrating vehicle trackworthiness to take advantage of computer modeling.The Track Safety Standards provide safety limits for maximum allowable track geometry variations for all nine FRA Track Classes — i.e., safety “minimums.” These limits serve to identify conditions that require immediate attention because they may pose or create a potential safety hazard. While these conditions are generally infrequent, they define the worst conditions that can exist before a vehicle is required to slow down. To promote the safe interaction of rail vehicles with the track over which they operate (i.e. wheels stay on track, and vehicle dynamics do not overload the track structure, vehicle itself, or cause injury to passengers), these conditions must be considered in the design of suspension systems. In particular, rail vehicle suspensions must be designed to control the dynamic response such that wheel/rail forces and vehicle accelerations remain within prescribed thresholds (VTI safety limits) when traversing these more demanding track geometry conditions at all allowable speeds associated with at particular track class.To help understand the differences in performance requirements (design constraints) being placed on the design of passenger equipment suspensions throughout the world, comparisons have been made between FRA safety standards and similar standards used internationally (Europe, Japan, and China) in terms of both allowable track geometry deviations and the criteria that define acceptable vehicle performance (VTI safety limits). While the various factors that have influenced the development of each of the standards are not readily available or fully understood at this time (e.g., economic considerations, provide safety for unique operating conditions, promote interoperability by providing a railway infrastructure that supports a wide variety of rail vehicle types, etc.), this comparative study helps to explain in part why, in certain circumstances, equipment that has been designed for operation in other parts of the world has performed poorly, and in some cases had derailment problems when imported to the U.S. Furthermore, for specific equipment that is not specifically designed for operation in the U.S., it helps to identify areas that may need to be addressed with other appropriate action(s) to mitigate potential safety concerns, such as by ensuring that the track over which the equipment is operating is maintained to standards appropriate for the specific equipment type, or by placing operational restrictions on the equipment, or both.In addition to these comparisons, an overview of the new FRA qualification procedures which are used for demonstrating vehicle trackworthiness is provided in this paper. These procedures, which include use of simulations to demonstrate dynamic performance, are intended to give guidance to vehicle designers and provide a more comprehensive tool for safety assessment and verification of the suitability of a particular equipment design for the track conditions found in the U.S.© 2014 ASME

Effect of Cant Deficiency on Rail Vehicle Performance

Simplified train models are analyzed to assess the relationship of unbalance on carbody acceleration and wheel unloading during steady state curving motion. In this paper a half-car model appropriate for both power cars and tilting coach cars is theoretically analyzed. Models of this type are useful for examining static lean requirements as well as margins of safety at higher cant deficiencies in the Track Safety Standards of the Federal Railroad Administration (FRA). The suspension systems modeled and analyzed include the following types: rigid, flexible, tilting actuation, and combined flexible and tilting actuation suspension. Simplified formulas are derived which can be used as an analysis tool by railroad designers to assess vehicle performance. Parametric results are presented for vertical wheel unloading and lateral carbody acceleration as a function of cant deficiency. Results show that incorporation of tilting systems, better suspension designs and better track quality, are necessary in order to provide an equivalent level of margin of safety for operations at higher cant deficiency. The relationship of these results to limits in the Track Safety Standards is discussed.Copyright

Failure analysis of railroad concrete crossties in the center negative flexural mode using finite element method

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.

High Speed Curving Performance of Rail Vehicles

On March 13, 2013, the Federal Railroad Administration (FRA) published a final rule titled “Vehicle/Track Interaction Safety Standards; High-Speed and High Cant Deficiency Operations” which amended the Track Safety Standards (49 CFR Part 213) and the Passenger Equipment Safety Standards (49 CFR Part 238) in order to promote vehicle track interaction (VTI) safety under a variety of conditions at speeds up to 220 mph. Among its main accomplishments, the final rule facilitates the expansion of higher speed passenger rail by revising the standards governing permissible operating speed in curves, allowing for higher cant deficiencies in all FRA Track Classes. To ensure safety is not diminished, the FRA Track Safety Standards require railroads to maintain their tracks to stricter track geometry standards whenever they operate at these higher curving speeds and cant deficiencies. These revisions were based on studies that examined the dynamic curving performance of various representative rail vehicles. This research investigates the steady-state curving performance of truck designs while traversing curves at various curving speeds and cant deficiencies. During steady-state curve negotiation, the axles of trucks generally offset laterally from the track centerline and develop angles of attack increasing the wheel-rail contact forces. Large lateral forces can develop, particularly in flange contact, resulting in increased wheel and rail wear, track panel shift, and the risk of derailment. Depending on the truck design, such forces become larger at higher cant deficiency. An understanding of the steady-state response of a rail vehicle in a curve is essential as it represents a significant part of the total dynamic response. The curving performance of an idealized rigid truck is analyzed using nonlinear analytical methods for a wide range of operating speeds and unbalance conditions. Emphasis is placed on higher speed curving and the results are used to interpret trends observed during recent field testing with Amtrak’s Acela High-Speed Trainset on the Northeast Corridor.

EXAMINATION OF VEHICLE PERFORMANCE AT HIGH SPEED AND HIGH CANT DEFICIENCY

In the US, increasing passenger speeds to improve trip time usually involves increasing speeds through curves. Increasing speeds through curves will increase the lateral force exerted on track during curving, thus requiring more intensive track maintenance to maintain safety. These issues and other performance requirements including ride quality and vehicle stability, can be addressed through careful truck design. Existing high-speed rail equipment, and in particular their bogies, are better suited to track conditions in Europe or Japan, in which premium tracks with little curvature are dedicated for high-speed service. The Federal Railroad Administration has been conducting parametric simulation studies that examine the performance of rail vehicles at high speeds (greater than 90 mph) and at high cant deficiency (greater than 5 inches). The purpose of these analyses is to evaluate the performance of representative vehicle designs subject to different combinations of track geometry variations, such as short warp and alinement.

Accurate Representation of the Rail Geometry for Multibody System Applications

The objective of this study is to examine the geometric description of the spiral sections of railway track systems, in order to correctly define the relationship between the geometry of the right and left rails. The geometry of the space curves that define the rails are expressed in terms of the geometry of the space curve that defines the track center curve. Industry inputs such as the horizontal curvature, grade, and superelevation are used to define the track centerline space curve in terms of Euler angles. The analysis presented in this study shows that, in the general case of a spiral, the profile frames of the right and left rails that have zero yaw angles with respect to the track frame have different orientations. As a consequence, the longitudinal tangential creep forces acting on the right and left wheels, in the case of zero yaw angle, are not in the same direction. Nonetheless, the orientation difference between the profile frames of the right and left rails can be defined in terms of a single pitch angle. In the case of small bank angle that defines the superelevation of the track, one can show that this angle directly contributes to the track elevation. The results obtained in this study also show that the right and left rail longitudinal tangents can be parallel only in the case of a constant horizontal curvature. Since the spiral is used to connect track segments with different curvatures, the horizontal curvature cannot be assumed constant, and as a consequence, the right and left rail longitudinal tangents cannot be considered parallel in the spiral region. Numerical examples that demonstrate the effect of the errors that result from the assumption that the right and left rails in the spiral sections have the same geometry are presented. The numerical results obtained show that these errors can have a significant effect on the quality of the predicted creep contact forces.

Acurate geometric description of spirals in railroad vehicle dynamic simulations

The objective of this study is to examine the geometric description of the spiral sections of railway track systems in order to correctly define the relationship between the geometry of the right and left rails. The geometry of the space curves that define the rails are expressed in terms of the geometry of the space curve that defines the track center curve. Industry inputs such as the horizontal curvature, grade, and super-elevation are used to define the track centerline space curve in terms of Euler angles. The analysis presented in this study shows that, in the general case of a spiral, the profile frames of the right and left rails that have zero yaw angle with respect to the track frame have different orientations. As a consequence, the longitudinal tangential creep forces acting on the right and left wheels, in the case of zero yaw angle, are not in the same direction. Nonetheless, the orientation difference between the profile frames of the right and left rails can be defined in terms of a single pitch angle. In the case of small bank angle that defines the super-elevation of the track, one can show that this angle directly contributes to the track elevation. The results obtained in this study also show that the right and left rail longitudinal tangents can be parallel only in the case of a constant horizontal curvature. Since the spiral is used to connect track segments with different curvatures, the horizontal curvature can not be assumed constant, and as a consequence, the right and left rail longitudinal tangents can not be considered parallel in the spiral region. Numerical examples that demonstrate the effect of the errors that result from the assumption that the right and left rail in the spiral sections have the same geometry are presented. The numerical results obtained show that these errors can have a significant effect on the quality of the predicted creep contact forces.© 2009 ASME