PSI - Issue 17

Paulo Morais et al. / Procedia Structural Integrity 17 (2019) 419–426

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Paulo Morais et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction

Railway track maintenance is a crucial aspect for the management of this type of transportation infrastructure regarding the technical and economic performance of the system. Track condition evaluation is usually carried out through labor-intensive visual inspection campaigns or with dedicated track inspection vehicles endowed with onboard vision systems, based on the standard EN 13848 (2019). However, both techniques do not provide useful information on the causes that lead to track performance degradation and thus, maintenance actions tend to be more corrective and less preventive. Aiming at improving railway assessment methods, some authors have proposed that the analysis of geometric condition should not be based only on comparisons between the geometric parameters values usually measured and their maximum prescribed values. It should take into account the dynamic response of the system, namely the rail wheel interactions and the vehicle velocity (Paixão et al., 2015). Over the last decades, there has been an increase of interest on the scientific and technical communities regarding the measurement of railway vertical deflection and assessment of its vertical stiffness. Vertical stiffness influences the carrying capacity of railway and its response regarding the passage of vehicles, thus representing an important parameter to assess geometric quality degradation of the railway and their respective maintenance costs (Le Pen et al., 2016; Quibel et al., 2010; INNOTRACK, 2008). Taking into account the limitations of the current methods, a project named COURSE was implemented under the partnership of LNEC and Mota Engil, Engenharia e Construção. S.A.. This project aimed at designing, developing and demonstrating the applicability of an innovative and integrated approach to assess railway performance. It also aimed to contribute to identify the causes of railway degradation, taking into account aspects related to the structural response due to the dynamic interaction between railway and vehicle. The developed approach should be able to continuously evaluate railway functional and structural parameters, with the use of an instrumented railway vehicle. This should allow for the proposed system to operate without disturbing railway infrastructure operation, thus providing a more efficient solution. Following the work presented in another paper submitted to ICSI 2019, this paper presents the methodology used in this project to process the acquired data and determine the relevant structural railway track parameters, such as railway track vertical stiffness, some geometrical properties of the rails and characteristic resonance frequencies of the vehicle-rail dynamic interaction. It also presents the results obtained from the first test using the prototype on a railway track under regular operation. For this purpose, a section of the track was instrumented with additional on site equipment to provide data for further system assessment and validation. The instrumented section comprised part of a bridge over Ribeira de São Martinho and the adjacent north embankment zone, near Alcácer do Sal, in Portugal. The data obtained from this proof of concept test, together with the results gathered from previous phases of this project, suggest that the proposed approach is adequate in this context. The proposed railway vertical stiffness evaluation method is based on measurements of rail vertical deformation due to the instrumented vehicle ’s own weight. The measurements are taken relative to the chassis of the vehicle that works like a moving referential. By measuring the distance between the chassis middle section and the railhead areas directly below, it is possible to obtain information related to the deformation of the railway when the vehicle passes over it. It is assumed that said railhead areas are sufficiently apart from the wheels and thus not deformed by the vehicle weight. When the vehicle deforms the railway line directly under the wheels due to its own weight, the distance between the middle section of the chassis and the railheads diminishes proportionally to railway stiffness. This distance shift is closely related to the average railway track deformation close to the measurement point. Then, by taking into account and removing the relative displacement between the chassis and the rails due to the vehicle’s suspension system it is possible to obtain an adequate estimate of the deformation imposed on the rails by the passage of the vehicle. The relative displacement is measured on four points between the shafts of the vehicle's wheels and points on the chassis directly above. In this process it is assumed that the wheels are undeformable and the measurements are as close as possible to the wheels. 2. Proposed data analysis methodology