1,721,067 research outputs found
A rolling stock-based system for catenary condition monitoring: Validation through numerical simulations on a rigid catenary
No full textCondition monitoring of rolling stock and infrastructure is becoming a key requirement for railway companies throughout the world, which are making a significant effort to equip commercial trains with diagnostic systems, to gather data daily instead of periodically as currently allowed by special-purpose diagnostic trains. This paper is part of a long-term work in which a diagnostic system, previously proposed by the authors, is being developed in cooperation with rolling-stock manufacturers, train operating companies and the Italian infrastructure manager. The system is able to monitor the pantograph and the overhead contact line through authomatic data acquisition and post processing in a wayside server, and should help shifting maintenance operations from time-based to condition based approaches. As a further application, the paper is focused on the detection of defects in a rigid overhead contact line. Numerical simulations of a healthy and a defective line are carried out to address the problem of signature definition for the identification of the defects
Damage identification in warren truss bridges by two different time–frequency algorithms
Full text linkRecently, a number of authors have been focusing on drive-by monitoring methods, exploiting sensors mounted on the vehicle rather than on the bridge to be monitored, with clear advantages in terms of cost and flexibility. This work aims at further exploring the feasibility and effectiveness of novel tools for indirect health monitoring of railway structures, by introducing a higher level of accuracy in damage modelling, achieve more close-to-reality results. A numerical study is carried out by means of a FE 3D model of a short span Warren truss bridge, simulating the dynamic interaction of the bridge/track/train structure. Two kinds of defects are simulated, the first one affecting the connection between the lower chord and the side diagonal member, the second one involving the joint between the cross-girder and the lower chord. Accelerations gathered from the train bogie in different working conditions and for different intensities of the damage level are analyzed through two time-frequency algorithms, namely Continuous Wavelet and Huang-Hilbert transforms, to evaluate their robustness to disturbing factors. Compared to previous studies, a complete 3D model of the rail vehicle, together with a 3D structural scheme of the bridge in place of the 2D equivalent scheme widely adopted in the literature, allow a more detailed and realistic representation of the effects of the bridge damage on the vehicle dynamics. Good numerical results are obtained from both the two algorithms in the case of the time-invariant track profile, whereas the Continuous Wavelet Transform is found to be more robust when a deterioration of track irregularity is simulated
Numerical investigation on train-bridge interaction after ship impact event: train running safety in different scenarios
No full textThis work presents a numerical study on the vehicle-bridge dynamic interaction in the catastrophic
event of a ship impact. In particular, the objective is to study the behavior of train running safety
coefficients as a function of bridge and vehicle mechanical properties. Two representative FE models of
a continuous beam bridge were built up, composed of six spans of 80 m, same deck section and different pier
heights. By combining this with the possibility of choosing between two distinct rail vehicles, namely Twindexx
and ICE, featured by different mechanical properties, it was possible to study the influence of these
parameters on the overall train running safety, after the occurrence of ship impact events. In addition, different
travelling speeds, different impact intensities were considered, and their effects investigated. Critical running
scenarios have been deepened, studying wheel-rail interaction and eventual detachment to physically interpret
the results provided by the computation of unloading and derailment coefficients
Sulla dinamica del veicolo ferroviario in rettilineo e in curva: influenza dell’accoppiamento sala-binario
No full textVision-based measurement of crack generation and evolution during static testing of concrete sleepers
No full textIn this paper, vision-based measurement system is developed to monitor the crack generation during the static test of concrete sleepers. In particular three point bending test described in the European Standard, EN 13230-2 [1] is considered. This test is the acceptance tests for concrete sleepers, which are declared in the mentioned Standard as “safety critical components for railway applications”. In this ambit, the validation and the check of the reliability of crack opening technique is a crucial point for the safety of passengers and infrastructure. The mentioned Standard imposes to measure the width of the main crack appearing on the sleeper and track it during the test, but it does not prescribe the measuring technique to be used or the maximum uncertainty that can be accepted. Crack width is often estimated manually, with the help of a handheld microscope. The measuring uncertainty is strongly related to the experience of the operator. In this work, a vision-based measuring technique, based on digital image correlation (DIC) technique, is proposed and validated. In the proposed approach, the crack path is first detected automatically, relying on the strain map generated by DIC, and then the crack width is estimated, relying on the displacement map. Finally, the proposed measurement approach is compared with the state-of-the-art technique based on the manual analysis of images acquired with a handheld microscope. The results show that the crack width measured with the proposed approach is compatible with the data obtained by the manual technique. Thanks to the proposed full-field measurement, the crack width can be estimated not only in a few manually detected points along the crack, but for the full length of the crack with an automatic procedure. Moreover, the proposed technique can be applied in an unmanned way, since the camera does not need to be manually moved along the sleeper side to detect the crack: it is mounted in a fixed position and the image processing software automatically detects the crack path and width. The operator is therefore not requested to work close to the sleeper during the loading, with advantages also for the safety
A 2D TBI model to study lateral dynamics in ship impact event
No full textThis paper presents a simplified 2D train-bridge dynamic interaction simula-tion tool to model the scenario of a ship collision against one of the piers of a bridge located on an oversea connection. Being rolling and lateral motion of each carbody of a train predom-inant in train motion following a ship collision event during train transit, only these two com-ponents of vehicle dynamics are considered. The bridge structure is modelled by means of a modal approach, ship impact is represented through a time dependent force, taken from lit-erature. The proposed simplified model enables a fast check, thanks to a time-efficient simula-tion, during early bridge design phase, in terms of lateral carbody acceleration, so as to get an early representation of the influence of ship collision events on train lateral dynamics. In fact, the proposed model allows the user to test and investigate a large variety of scenarios, in terms of train and structure properties as well as loading features, in a fast and efficient way, without loss of relevant information. Moreover, this approach would enhance structure and train dynamic interaction understanding, highlighting the role played by train lateral dynam-ics and its interaction with bridge dynamics, in critical scenarios
An acoustic emission-based approach to structural health monitoring of pre-stressed concrete railway sleepers
Full text linkRailway sleepers represent an essential element of the track; indeed, their structural integrity is closely related to important technical and safety issues. Today, periodical visual inspections are the only method applied to check the status of sleepers but are limited to visible surfaces, whereas the early detection of in-service cracks in the whole volume of sleepers would provide great advantages in terms of maintenance and management. The aim of the paper is to propose an acoustic emission (AE)-based structural health monitoring (SHM) approach that is able to detect the initiation and propagation of cracks in in-service pre-stressed concrete sleepers. The investigation is carried out in the laboratory, comparing the results obtained by acoustic emission monitoring and digital image correlation when subjecting pre-stressed concrete sleepers, taken from production, to both static and cyclic loads. The main points dealt with in the paper include the sensitivity of acoustic emission to detect damage development and the signal processing approach needed for defining effective damage indexes. Given the encouraging results, the paper is the first step in developing an affordable monitoring system, to be embedded into sleepers, that is able to be part of a complete track monitoring system
On situ vibration based structural health monitoring of a railway steel truss bridge: a preliminary numerical study
Full text linkRailway network is subject to increasing travelling loads and traffic frequency. In
addition, since most of the bridges were built in the last century, they are subject to ageing and
degradation. It is therefore necessary to develop proper structural health monitoring systems
that can support periodical visual inspections. In this context, direct monitoring systems
represent an important and promising solution for structural health monitoring purposes. This
paper is the result of a numerical study performed on a 3D FE bridge model based on an
existing structure: the latter is a Warren truss railway bridge, located in Northern Italy, built
few years after the end of the second world war. The purpose of the study is to numerically
evaluate the effectiveness in damage detection and localization of different vibration-based
techniques. This analysis has been performed for a set of different damage scenarios, suggested
by the infrastructure managers
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