Morad Shadfar

Rail welds are considered as the weak part of a railway track. Their defects and health can directly affect wheel-rail interaction, track safety, and reliability. Current practices for rail welds health assessment are based on 2D vertical and lateral wear measurement which needs time and track blocking. The development of inertia-based condition monitoring methods such as measuring axle box acceleration (ABA) comes with a crucial question on criteria or index for each rail track component health monitoring. In this study, an index for evaluation of rail weld health is proposed through integrated numerical and field experiment data within a metro line using the ABA technique. The relationship between the speed, wheel structural vibration, and acceleration amplitude is investigated using fast Fourier transformation (FFT) and a nonlinear neural network principal component analysis (PCA) model. An index is introduced to assess weld severity level based on the statistical method. This index is simple and applicable for maintenance practice.

As track components deteriorate, their interaction dynamic response will alter accelerations on the train. Measuring acceleration on train components is a method to conduct condition monitoring of track defects. The measured signal can be used for the detection of rail surface defects which implement impacts on measured accelerations. In this paper, the axle-box acceleration (ABA) is measured in a subway as a case study. Fourier transform (FFT), empirical mode decomposition (EMD) and ensemble EMD (EEMD) methods are used to study accelerations relative to the track. Wheel frequencies are calculated using finite element method (FEM) to determine frequency couplings. Velocity-dependent/independent components and source of excitation of the measured signal are distinguished. Results indicated that the FFT approach can be applied for both velocity-dependent and velocity-independent vibration components for frequencies up to 680 Hz. Also, the EEMD method can be used to distinguish the impact component of the measured signal.

When a train passes over bridges, the magnitude of forces and accelerations is altered due to sudden changes in the track stiffness. These forces can change with the variation in operational parameters and are effective particularly in high-speed passenger trains, when studying ride index parameter. In addition, by increasing the speed, old bridge structures could fall into resonance, which has harmful consequences for both bridge and ride comfort index. Moreover, to harmonize the old bridges with the new operational conditions dynamic behavior of the vehicle and ride comfort need to be taken into account. In this paper, coupled vertical and roll vibration of a horizontally curved bridge are considered. During pass over the bridge, acceleration and ride comfort of a passenger vehicle are studied. The eccentric vertical and lateral forces are the major excitation sources in the analysis, an issue that is rarely noticed in the literature. A multi-body model of a normal wagon is built in three dimensions, passing over a horizontally curved bridge. The governing equations of the vehicle–bridge system are written, taking into account the wheel–rail interactions. The major variables are the cant, train speed, track quality, and radius of curvature. The paper studies the effects of the prescribed variables on ride comfort. The results show that track quality and cant have considerable influences on ride comfort index. The ride comfort is improved when the speed is approached to a so-called equivalent speed.

Employing a coupled model for vehicle–track interaction, this paper presented the dynamic analysis of railway track system in the presence of weld irregularities with different geometric profiles in two parallel rails. A 3D model of a standard railway wagon running on a ballasted track system is used to examine the vibrations of the system under track irregularities. Four samples of measured rail profiles at rail welds are considered as the source of dynamic excitations, in which the profiles of parallel rails are unequal. Hence, the individual profiles of left/right rails are imported into the numerical model, taking into account the nonuniform conditions of rail welds in both sides of the railway track. The dynamic responses of the track system caused by irregularities at welds are studied by performing the time-domain vibration analysis. The time histories of the nodal responses under various weld scenarios (measured in an actual railway track site) are recorded. Finally, the peak responses of dynamic forces along the track are determined for left/right rails. The results of dynamic simulations in various weld scenarios are compared and the values of dynamic amplification factors (DAFs) are evaluated. Such findings provide an estimation for the levels of dynamic forces occurring under impact loading conditions of nonuniform rail welds in left/right rails.

Employing a dynamic model of the railway wagon in three dimensions, this paper presents the results of dynamic wheel–rail forces under the presence of track irregularities. A mathematical model of the wagon system is developed using dynamic equations of the components, taking into account the vertical (bounce), pitch and roll motions of the system. The model examines the dynamics of the wagon system under arbitrary rail irregularities. The spectra of rail surface irregularities are fed into the vehicle model to extract the time histories of dynamic forces between the wheel and the rail. Using the irregularity spectra of left/right rails, vibration of the wheelsets is studied for the bounce–roll motions. The dynamic contact forces between wheels and rails are determined for three examples of the measured irregularities. Moreover, three V-shape defects are modelled as examples of the singular defects on rail surface. The results of dynamic simulations confirm the large amounts of impact forces due to the presence of rail irregularities, particularly for the cases with much unevenness between the left/right profiles.

A mathematical model of the vehicle–track interaction is developed to investigate the coupled behaviour of vehicle–track system, in the presence of uneven irregularities at left/right rails. The railway vehicle is simplified as a 3D multi-rigid-body model, and the track is treated as the two parallel beams on a layered discrete support system. Besides the car-body, the bogies and the wheel sets, the sleepers are assumed to have roll degree of freedom, in order to simulate the in-plane rotation of the components. The wheel–rail interface is treated using a nonlinear Hertzian contact model, coupling the mathematical equations of the vehicle–track systems. The dynamic interaction of the entire system is numerically studied in time domain, employing Newmark's integration method. The track irregularity spectra of both the left/right rails are taken into account, as the inputs of dynamic excitations. The dynamic responses of the track system induced by such irregularities are obtained, particularly in terms of the vertical (bounce) and roll displacements. The numerical model of the present research is validated using several benchmark models reported in the literature, for both the smooth and unsmooth track conditions. Four sample profiles of the measured rail irregularities are considered as the case studies of excitation sources, examining their influences on the dynamic behaviour of the coupled system. The results of numerical simulations demonstrate that the motion of track system is significantly influenced by the presence of uneven irregularities in left/right rails. Dynamic response of the sleepers in the roll direction becomes more sensitive to the rail irregularities, as the unevenness severity of the parallel profiles (quantitative difference between left and right rail spectra) is increased. The severe geometric deformation of the track in the bounce–pitch–roll directions is mainly related to such profile unevenness (cross-level) in left/right rails.

Generally, Railway bridges are long structures which have different responses against different loads of train. Applied loads of train on railroad bridges are different in terms of axle loads speed, and annual passed tonnages and they have quite different dynamic behavior in comparison with road bridges. Most researches are basically focused on the quasi-static analysis. Therefore in these researches, the effect of load speed has been neglected. Nowadays with the development of rail transport systems, the study of dynamic behavior of bridges under the different load speed is necessary. Also, the dynamic behavior of curved bridges is different than straight ones. In this paper, vertical and torsional vibrations of a curved beam have been studied with considering vertical, horizontal load and eccentricity of load than centerline of bridge. Also the considered parameters in this research are radius of curvature, track irregularity, vehicle speed and bridge span.

In this paper an open wagon equipped with three pieces bogies has been simulated as multi body dynamics model with non-linear effects of wedges and structural clearances using Universal Mechanism software. Analyses have been performed on closed loop track with tangent and curved sections considering random irregularities in the vertical and lateral directions of the track. Simulation results are used to calculate the friction work, wheel wear depth and worn wheel profiles for different velocities and radii of curvature. “Specht” model based on “Archard's Theory” is used for wear calculations. The wear depth of outer wheels is assessed to determine the effect of velocity, track curvature and Pivot friction of bogie on the wear pattern of wheels. The results show that Pivot friction has a great effect on the non-uniform wear of wheels even in short distances and the friction work is found to be dependent on the velocity.