M. Oregui

An investigation into the vertical dynamics of tracks with monoblock sleepers with a 3D finite-element model

This paper investigates the vertical dynamic behavior of railway tracks with monoblock sleepers. Whole- and half-track finite element (FE) models are presented in which the rails and sleepers are represented with their nominal 3D geometry using solid elements. The railpad encompasses the rail seat area modeled as multiple spring–damper pairs. The 3D FE models are employed for three purposes. First, the stiffness and the damping of the railpad and ballast are derived by fitting the simulations to a set of field hammer test measurements. Second, the origins of six of the seven main characteristics are identified. Third, the influence of the railpad representation on the track’s dynamic response is studied. The results show that, in contrast to the 3D FE half-track model, the 3D FE whole-track model reproduces six of the seven main vertical track characteristics with a maximum deviation of 10% from the measured frequencies. The seventh characteristic is reproduced at approximately the measured frequency when the frequency-dependent stiffness of the railpad is considered. This model can be used to derive track parameters that will aid in the study of track degradation.

Axle box acceleration for health monitoring of insulated joints: A case study in the Netherlands

This paper presents preliminary results towards an automated monitoring system for the quality assessment of insulated rail joints based on axle box acceleration (ABA) measurements. ABA signals from all the wheels of the measuring train (trailing and leading wheels, right and left rails) are processed to extract those characteristics that better represent the quality and the state of the insulated joint. We compared the responses of different insulated joints in good condition, and three cases of joints in poor condition with visible surface degradation, fastening damage and damage to the insulation layer. Different indicators are used to classify the joint condition, the most relevant being the maximum ABA response, and some frequency bands in the ABA power spectrum. Track inspections and hammer tests were performed to collect validation data of the studied insulated joints.

Sensitivity Analysis of Railpad Parameters on Vertical Railway Track Dynamics

This paper presents a sensitivity analysis of railpad parameters on vertical railway track dynamics, incorporating the nonlinear behavior of the fastening (i.e., downward forces compress the railpad whereas upward forces are resisted by the clamps). For this purpose, solid railpads, rail-railpad contact and preloaded springs are defined in a three-dimensional (3D) finite-element track model. In addition, railpads are modeled as Prony series so that measured frequency-dependent railpad properties for different clamp toe load, temperature, aging, and railpad type are considered. Through sensitivity analysis using time-domain and frequency-domain responses, the influence of the railpad parameters on the global track response is investigated. Railpad type, toe load and aging are identified as the most relevant parameters in the frequency range of 300-3,000 Hz. Furthermore, the information obtained over track response changes due to fastening loosening and railpad wear could be used for monitoring the condition of fastenings.