Numerical simulation of a bridge-subgrade transition zone due to moving vehicle in Shuohuang heavy haul railway

When a vehicle passes through the bridge-subgrade transition zone, the dynamic effects between the vehicle and infrastructure, including track, subgrade will increase greatly. In this paper, a three dimensional model of bridge-subgrade transition zone under moving vehicle in Shuohuang Railway is established. The vehicle is idealized as 18 degree of freedoms multi-body system and the bridge-subgrade transition zone is built using ABAQUS software. With this model, some dynamic responses of bridge-subgrade transition zone under moving vehicle with and without track irregularity are computed. It is concluded that the track irregularity can amplify the dynamic responses in the transition zone significantly

The assessment of soil depth sensitivity to dynamic behavior of the Euler-Bernoulli beam under accelerated moving load

Dynamic behavior is one of the most crucial characters in the railways structures. One of the items which leads to precise identification of the dynamic behavior of railways is the soil depth beneath them. In this paper, an Euler-Bernoulli beam on a finite depth foundation under accelerated moving load is presented. The dynamic equilibrium in the vertical direction is only regarded in accordance with the factor of finite beams. In this study, the dynamic equilibrium of the soil in the vertical direction and the sensitivity of soil depth are considered. The governing equations are simulated by using Fourier transform method. Eventually, by considering the sequences of shear waves, and different kinds of damping, displacement of the beam is obtained for the various acceleration, times and soil depth. As a result, it is shown that, higher acceleration is not dramatically effective on the beam displacement. Also, foundation inertia causes a significant reduction in critical velocity and can augment the beam response

Numerical simulation of a metro vehicle running over rail with fastening system failure using finite element method

In this paper, the dynamic responses of a moving vehicle traversing over railway track with fastening system failure were investigated using a vehicle/track coupling system model. In this model, the moving vehicle is developed by multi-body dynamics, and the direct fixation track is modeled by finite element method, where the rail is treated as an Euler-Bernoulli beam supported by fastening systems. An invalidation factor is used to determine the failure of the fastening system. The Hertzian spring is adapted to model the wheel/rail contact force between the moving wheel set and the rail. The proposed vehicle/track system model is verified with some field testing results in Zhengzhou subway. To solve the vehicle/track system model with nonlinear contact force, an iterative procedure is proposed. The effects of fastening system failure on the responses of the vehicle and track are investigated. It indicates that the wheel/rail contact force varies abruptly when the vehicle passing over the fastening system failure zone, which result in track deterioration

Potential of neural networks for maximum displacement predictions in railway beams on frictionally damped foundations

Since the use of finite element (FE) simulations for the dynamic analysis of railway beams on frictionally damped foundations are (i) very time consuming, and (ii) require advanced know-how and software that go beyond the available resources of typical civil engineering firms, this paper aims to demonstrate the potential of Artificial Neural Networks (ANN) to effectively predict the maximum displacements and the critical velocity in railway beams under moving loads. Four ANN-based models are proposed, one per load velocity range ([50, 175] ∪ [250, 300] m/s; ]175, 250[ m/s) and per displacement type (upward or downward). Each model is function of two independent variables, a frictional parameter and the load velocity. Among all models and the 663 data points used, a maximum error of 5.4 % was obtained when comparing the ANN- and FE-based solutions. Whereas the latter involves an average computing time per data point of thousands of seconds, the former does not even need a millisecond. This study was an important step towards the development of more versatile (i.e., including other types of input variables) ANN-based models for the same type of problem

Applicability of a Three-Layer Model for the Dynamic Analysis of Ballasted Railway Tracks

In this paper, the three-layer model of ballasted railway track with discrete supports is analyzed to access its applicability. The model is referred as the discrete support model and abbreviated by DSM. For calibration, a 3D finite element (FE) model is created and validated by experiments. Formulas available in the literature are analyzed and new formulas for identifying parameters of the DSM are derived and validated over the range of typical track properties. These formulas are determined by fitting the results of the DSM to the 3D FE model using metaheuristic optimization. In addition, the range of applicability of the DSM is established. The new formulas are presented as a simple computational engineering tool, allowing one to calculate all the data needed for the DSM by adopting the geometrical and basic mechanical properties of the track. It is demonstrated that the currently available formulas have to be adapted to include inertial effects of the dynamically activated part of the foundation and that the contribution of the shear stiffness, being determined by ballast and foundation properties, is essential. Based on this conclusion, all similar models that neglect the shear resistance of the model and inertial properties of the foundation are unable to reproduce the deflection shape of the rail in a general way.publishersversionpublishe

Neural network-based formula for shear capacity prediction of one-way slabs under concentrated loads

According to the current codes and guidelines, shear assessment of existing reinforced concrete slab bridges sometimes leads to the conclusion that the bridge under consideration has insufficient shear capacity. The calculated shear capacity, however, does not consider the transverse redistribution capacity of slabs, thus leading to overconservative values. This paper proposes an artificial neural network (ANN)-based formula to come up with estimates of the shear capacity of one-way reinforced concrete slabs under a concentrated load, based on 287 test results gathered from the literature. The proposed model yields maximum and mean relative errors of 0.0% for the 287 data points. Moreover, it was illustrated to clearly outperform (mean Vtest / VANN =1.00) the Eurocode 2 provisions (mean VE,EC / VR,c =1.59) for that dataset. A step-by-step assessment scheme for reinforced concrete slab bridges by means of the ANN-based model is also proposed, which results in an improvement of the current assessment procedures

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells

Viability and Applicability of Simplified Models for the Dynamic Analysis of Ballasted Railway Tracks

The numerical models of the railway track are fundamental tools for the study of their dynamic behaviour, with implications for the safety and comfort of rail transport and the degradation and need for maintenance of the track. The importance of these models has increased alongside the speed and capacity of the railway vehicles over the last decades. Although the use of three-dimensional finite element models is becoming common practice, simplified models are still relevant, due to their simplicity of implementation and results interpretation, and low computational cost. However, the general validity of these models has not yet been demonstrated in the relevant literature. The present thesis aims to establish the applicability and viability of such simplified models in the analysis of the dynamic behaviour of the ballasted railway track. The following questions are considered: 1. Are these models able to approximate the real rail displacement due to the passage of rail vehicles, despite their simplicity? 2. If yes, for which situations (i.e., track properties and loading conditions) can they be used reliably? 3. In these situations, is it possible to define adequate parameters for the simplified models based on the track’s geometry and mechanical properties? To that end, three linear elastic models are implemented: a detailed three-dimensional finite element model, a one-dimensional beam in discrete supports model, and a one-dimensional beam on elastic foundation model. Transient and steady-state dynamic solutions for a load moving at moderate and high speed are obtained. The vertical displacement of the rail is chosen as the reference to measure the equivalence between the models, since it is a common element between all models and is the interface between the load and the track. The three-dimensional model is validated by comparison with published experimental measurements. Its results cover a representative range of the properties of the ballast and subgrade, and are used as a reference to calibrate the simplified models using genetic algorithms and non-linear programming. It is concluded that a good approximation to the reference solution can be achieved, particularly when the load moves slower than the velocity of propagation of the elastic waves in the soil. For high velocities and/or soft soils, the wave propagation becomes more relevant to the dynamic behaviour of the track, and the simplified models become less reliable. Following a review of the existing literature, theoretical expressions for the determination of the parameters of the simplified models are proposed. It is concluded that these are suitable for the beam on discrete supports model, but not for the beam on elastic foundation model, whose optimum parameters are less consistent across the different properties of the track and load speeds