Derailment Criterion Research Articles

Running safety of high-speed railway vehicles on the elastoplastic track-subgrade-bridge system under near-fault pulse-type earthquakes

In this study, the running safety assessment (RSA) of high-speed railways is carried out, with the wheel lift being the derailment criterion. Seventy near-fault pulse-type earthquakes (NFPTEs) are imposed on an elastoplastic vehicle-track-bridge coupled model with elastoplastic supports and shear keys. Since the bridge length in the simulation model is limited by the 14-span high-speed railway simply supported bridge prototype with subgrades and a CRTS II track plate, it is difficult for the vehicles going through the full time-history of ground motions while passing over the bridge. Therefore, the excitation-input-time (EIT) analysis is conducted herein, and it is found that the effects of EIT on RSA under NFPTEs are significant and, as such, cannot be ignored. The EIT analysis also shows that the appearance times and EITs of peak ground acceleration and peak ground velocity of NFPTEs significantly affect the RSA results. In order to reveal and describe the potential relationship between dynamic responses of rail and wheel lift, dynamic contact point responses (DCPRs) are also proposed, and after comparison with the traditional dynamic responses, including rail deformations and displacements, the dynamic contact point velocity in Y-direction (DCPV-Y) are selected for developing of relationship with wheel lift and RSA limitation zone proposal.

On train speed reduction in circumstances of thermally-induced railway track buckling

Abstract Increasing heatwave spells associated with global warming profoundly affect the propensity of continuously-welded railway tracks to buckle laterally in a horizontal plane. Train derailments in the presence of buckled tracks endanger the community and are costly to repair. Track buckling is a localization phenomenon, and the amplitude of the buckle increases in the post-buckling range. Because of this, it may not be possible for a train crew at speed to observe a small buckle, or indeed to stop the train if a larger buckle is encountered. There is, therefore, a need to be able to assess the derailment vulnerability as a train passes over a buckled railway track. This paper proposes a finite element modelling of passenger cars and the required speed reduction in circumstances in which railway buckling has occurred. The model of the passenger car is composed of three parts - a carriage, bogies and wheelsets - being connected by springs and dampers. The response of the passenger car is obtained by adopting implicit dynamic analysis, with the analysis being undertaken in the presence of four buckled configurations obtained from non-linear structural analysis. The Weinstock derailment criterion is invoked to describe the vulnerability to derailment, and the derailment index so calculated is shown to increase significantly with the train speed. The effects of the buckle amplitude, the rail size and the ballast resistance on the safe speed are investigated, with the amplitude of the buckle being shown to be the most significant parameter at a particular speed.

Safety evaluation for railway vehicles using an improved indirect measurement method of wheel–rail forces

The wheel–rail force measurement is of great importance to the condition monitoring and safety evaluation of railway vehicles. In this paper, an improved indirect method for wheel–rail force measurement is proposed to evaluate the running safety of railway vehicles. In this method, the equilibrium equations of a suspended wheelset are derived and the wheel–rail forces are then be obtained from measured suspension and inertia forces. This indirect method avoids structural modifications to the wheelset and is applicable to the long-term operation of railway vehicles. As the wheel–rail lateral forces at two sides of the wheelset are difficult to separate, a new derailment criterion by combined use of wheelset derailment coefficient and wheel unloading ratio is proposed. To illustrate its effectiveness, the indirect method is applied to safety evaluation of railway vehicles in different scenarios, such as the cross wind safety of a high-speed train and the safety of a metro vehicle with hunting motions. Then, the feasibility of using this method to identify wheel–rail forces for low-floor light rail vehicles with resilient wheels is discussed. The values identified by this method is compared with that by Simpack simulation for the same low-floor vehicle, which shows a good coincidence between them in the time domain of the wheelset lateral force and the wheel–rail vertical force. In addition, use of the method to determine the high-frequency wheel–rail interaction forces reveals that it is possible to identify the high-frequency wheel–rail forces through the accelerations on the axle box.

Dynamical and Geometrical Aspects Regarding the Behaviour of a Railway Vehicle Running on Curved Routes

The authors analyze the dynamical and geometrical aspects regarding the behaviour of a locomotive running on curved routes . There were taken into account all the possible disturbing effects and all the forces and torques acting on the bogie frame and on the coaches or carriages. A sophisticated calculus model is proposed for the analytic investigation. The guidance and the vertical forces on the wheel, the derailment criterion and the spring vibration damping are the main subjects of the investigation.

고속철도교의 지진 시 이동하중 해석을 통한 열차 운행규정 검토

최근 철도구조물의 내진에 대한 검토가 다양하게 이루어지고 있다. 하지만 열차의 탈선을 방지하기 위한 국내 고속철도 운행규정에 대한 연구는 미비한 실정이다. 국내 고속철도 운행규정은 지반가속도를 측정하여 사용하는 프랑스 규정을 기초로 설정되었지만, 지반가속도를 측정하여 사용하지 않고 교량 상부에 설치된 지진감시센서에서 측정된 가속도를 사용하여 지진 시 운행경보를 발령한다. 따라서 구조물에 의해 증폭되는 가속도로 열차운행을 제한함으로써 규모가 작은 지진에서도 열차가 운행할 수 없는 경보가 발령되어 열차운행에 경제적인 손실이 발생될 가능성이 크다. 본 논문에서는 PSC(Prestressed Concrete) 박스 철도교량을 대상으로 이동하중 해석, 지진하중 해석 및 지진 시 이동하중 해석을 수행하여 철도설계기준에서 제시하는 동적안정성 평가기준과 철도운행에 관한 안전지침에서 규정하는 지진 시 열차 운행규정을 비교하여 고속철도 운행규정의 적절성을 분석하였다. A large number of researches have been conducted on seismic resistant design of railway bridges. However, research on the running regulation of high-speed train during earthquake is limited. The current running regulation of high-speed train during earthquake was based on the French regulation. Accelerations were measured from the deck rather than ground acceleration, which results in reaching the limit value of the running regulation frequently due to amplified acceleration. This study investigates the dynamic behavior of high-speed railway bridges under earthquake. Analysis results are then compared against dynamic safety criterion in Korean railway design standard and train operation limits of safety instructions on the train operation. It is observed that both dynamic safety and derailment criterion are satisfied when the high-speed train runs over the bridge with the critical speed and under the earthquake level of serviceability limit state.

Analysis of derailment criteria

Rail transportation systems include high-speed rail, rapid mass transit systems, rail freight, and light-rail transit systems are generally wheel-on-rail systems. Thus, the evaluation of the risk of a derailment is a critically important issue; consequently, researchers have endeavored to identify and evaluate an effective derailment criterion. Nadal’s quotient has been widely adopted in the assessment of the risk of a derailment. Although recent studies have sometimes criticized that criterion, it still serves as the basis of new criteria and regulations. This article seeks to investigate the problems associated with various derailment criteria, to point out their features and deficiencies, and then to theoretically illustrate their differences. It has been found that the Weinstock criterion does not correctly consider the tread contact wheel, with the revised Weinstock criteria being proposed to correct that problem. Furthermore, a new criterion has been developed that solely considers the horizontal component of the tangential force at the contact point. The new criterion was compared with the wheel load reduction criterion and other criteria to justify the derailment assessments.

An angle of attack-based derailment criterion for wheel flange climbing

A three-dimensional equilibrium model of a wheelset is created that takes the geometrical contact and non-linear creep force between the wheel and rail into account. This model can thus be used to study derailment conditions during flange climbing. To ensure the validity of Nadal’s criterion at small and negative angles of attack, the effects of the angle of attack and friction coefficient on an “equivalent friction coefficient”, which is defined as the ratio of the lateral creep force to the normal force, are studied. Using the results of the wheelset equilibrium equation, two curve-fitted formulas for the equivalent friction coefficient are generated in terms of the angle of attack and friction coefficient using, respectively, the Shen–Hedrick–Elkins creep theory and FASTSIM approach. A derailment criterion is proposed based on the curve-fitted equivalent friction coefficients, which takes the angle of attack, friction coefficient and contact angle into consideration. The effectiveness of the proposed criterion is verified through numerical comparisons with wheelset equilibrium equations for different contact angles and friction coefficients, and through experimental comparisons with scaled tests made by Japanese National Railways and full-scale field testing at the Transportation Technology Center, Inc.

A new criterion for assessment of train derailment risk

A new criterion for prediction of train derailment is presented in this article. A three-degrees-of-freedom (3 DOF) wheelset model is used to identify the main dynamic parameters that affect wheelset derailment. Using these parameters and conventional definition of derailment coefficient, a new criterion for prediction of wheelset derailment is introduced. The proposed criterion, in addition to providing the required precision in prediction of wheel set derailment, requires measurements that are easy to perform. To evaluate the capability of the new criterion in prediction of derailment, a full wagon model with 48 DOF moving on a track with different random irregularities was used. The track is assumed to be mounted on a viscoelastic foundation. The wagon model is a three-dimensional, non-linear model of a train passenger car. The model includes non-linear elements for primary and secondary suspension systems. Friction and slack between elements, the centre pivot with kinematics constraints, forces between pads, and bolster are also included in this model. The motion of the wagon on tangent and curved tracks is simulated for different travel speeds. Derailment coefficient and a new derailment criterion are used to investigate the possibility of wheelset derailment in each case. The study shows that the new criterion can very well predict wheelset derailment and can duplicate the predictions by conventional derailment coefficient ( Y/ Q).

Influence of creep forces on the risk of derailment of railway vehicles

The derailment mechanism in a railway vehicle is a complex mechanical phenomenon which has been, and still is, the subject of intense research activity due to the serious consequences it can entail. Since Nadal deduced his well-known formula, many researchers have put forward alternative equations which all attempt to move closer to the data obtained experimentally. This paper provides a summary of the best known and draws up a new formulation based on the theoretical 3-D study of creep forces emerging from the contact patch of the wheel likely to derail. It also provides an in-depth analysis of the role played by spin creepage, including its effect on obtaining theoretical derailment limits, which are more realistic than those obtained using Nadal's formula. Finally, a new derailment criterion is proposed. This new criterion leads to less conservative values than Nadal's equation for zero yaw angles. When the yaw angle is high enough, the results obtained are coincident with those predicted by Nadal's equation.

Theory of random energy analysis for train derailment

Three fundamental problems in the calculation of train derailment abroad and at home were pointed out and the solutions to these problems were presented. The theory of random energy analysis for train derailment was suggested. The main contents of this theory are as follows: geometric criterion of derailment; method of random energy analysis of transverse vibration of train track system; mechanism of derailment and energy increment criterion for derailment evaluation; calculation of the entire derailment course of train. This theory is used to calculate a case of freight train derailment, which corresponds to an actually occurring accident. Another derailment test, in which the train is judged not to be derailed, is calculated and the maximum vibration response is well correspond to the test results. And the effectiveness and practicability of the theory are proved by the two calculated cases.