A wheel-rail contact formulation for analyzing the train-structure nonlinear interaction that takes into account the wheel and rail geometry is proposed. Most of the existing methods treat the contact forces as external forces, whereas the present formulation uses a finite element to model the behavior in the contact interface, based on Hertz's theory and Kalker's laws. The equations of motion are complemented with constraint equations that relate the displacements of the vehicle and structure, being the complete system solved directly using an optimized algorithm. The formulation is validated with experimental data from a test performed on a rolling stock plant.

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The gradual deterioration of train wheels can increase the risk of failure and lead to a higher rate of track deterioration, resulting in less reliable railway systems with higher maintenance costs. Early detection of potential wheel damages allows railway infrastructure managers to control railway operators, leading to lower infrastructure maintenance costs. This study focuses on identifying the type of sensors that can be adopted in a wayside monitoring system for wheel flat detection, as well as their optimal position. The study relies on a 3D numerical simulation of the train-track dynamic response to the presence of wheel flats. The shear and acceleration measurement points were defined in order to examine the sensitivity of the layout schemes not only to the type of sensors (strain gauge and accelerometer) but also to the position where they are installed. By considering the shear and accelerations evaluated in 19 positions of the track as inputs, the wheel flat was identified by the envelope spectrum approach using spectral kurtosis analysis. The influence of the type of sensors and their location on the accuracy of the wheel flat detection system is analyzed. Two types of trains were considered, namely the Alfa Pendular passenger vehicle and a freight wagon.

This article presents an accurate, efficient and stable algorithm to analyze the nonlinear vertical vehicle-structure interaction. The governing equilibrium equations of the vehicle and structure are complemented with additional constraint equations that relate the displacements of the vehicle with the corresponding displacements of the structure. These equations form a single system, with displacements and contact forces as unknowns, that is solved using an optimized block factorization algorithm. Due to the nonlinear nature of contact, an incremental formulation based on the Newton method is adopted. The vehicles, track and structure are modeled using finite elements to take into account all the significant deformations. The numerical example presented clearly demonstrates the accuracy and computational efficiency of the proposed method.

SUMMARYA study about the running safety of trains moving over bridges subjected to earthquakes is presented. The study focuses on moderate earthquakes with relatively small return periods and high probability of occurrence. The analyses are performed using a nonlinear train-bridge interaction method proposed by the authors, being the running safety evaluated with safety criteria existent in the literature. The influence on the train running safety of the seismic intensity levels, train running speed, and track quality is evaluated. Because no significant nonlinearity is likely to be exhibited in the columns for moderate levels of seismicity, the analyses are performed in the elastic domain. However, the reduction in the columns stiffness due to cracking is accounted, and a methodology to compute their effective stiffness is proposed.

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