The main area of research of this work is the diagnostics of the rail infrastructure, bridges in particular. The purpose of the dissertation is, first of all, to formulate a diagnostic method which uses the on-board acceleration signals to localise the damaged section. Secondly, the goal is to determine the most relevant variables of the problem and to analyse to which extent they affect the effectiveness of the diagnostic method. The time response of the bridge has been calculated with a Matlab script for finite element analysis. The bridge-vehicle interaction has been modelled with increasing complexity: at first a single point force is considered to represent an axle; then the whole carriage is considered as a sequence of four point forces; and at last one bogie was taken into account as a sprung and damped 4 DOF moving system (with rail roughness). The proposed damage localisation method is based upon a comparison between the calculated acceleration signals from the damaged bridge with the ones of the undamaged one. The signals are filtered using a moving mean, to remove the contribution of the first bridge eigenfrequency. It appears that high levels of rail irregularity generate a relevant excitation of the structure, which results in high amplitudes of acceleration, which overwhelm the singularity due to damage. Moreover, the method is not efficient at high speeds, since the duration of the observation is limited. This numerical work should be followed by a field testing campaign to investigate the real applicability of the method and should be compared with other diagnostic techniques found in literature.
Il campo di ricerca in cui l'elaborato si posiziona è quello della diagnostica di ponti ferroviari. Lo scopo della tesi è, prima di tutto, proporre una strategia di analisi dei segnali di accelerazione misurati a bordo treno per localizzare il danno. In secondo luogo, l'obiettivo del lavoro consiste nel determinare quali sono le variabili più rilevanti del problema e in quale misura esse incidono sul funzionamento del metodo di diagnosi. La risposta del ponte nel tempo è stata calcolata tramite un codice Matlab per l'analisi ad elementi finiti. L'interazione tra veicolo e ponte è stata modellata con crescente complessità: dapprima è stata considerata una singola forza viaggiante per rappresentare un assile; poi un treno di quattro forze per rappresentare una carrozza; infine un sistema massa molla smorzatore a 4 gradi di libertà (con irregolarità di binario) per rappresentare la dinamica di un carrello. Il metodo diagnostico che è stato proposto si basa sul confronto tra le accelerazioni nel tempo calcolate con i dati del ponte danneggiato e quelle calcolate per lo stesso ponte privo di difetti. Tali segnali sono filtrati con una media mobile per rimuovere il contributo della prima frequenza propria del ponte. È risultato che alti livelli di irregolarità eccitano la struttura in misura maggiore, genereando elevate accelerazioni rispetto alla singolarità dovuta al danno. Inoltre, alle alte velocità il metodo perde efficacia. A valle di questo elaborato numerico occorre svolgere una campagna sperimentale per valutare la applicabilità pratica del metodo e confrontarne l'efficienza rispetto ad altre tecniche di diagnosi trovate in letteratura.
Diagnostics of a railway bridge by means of train on-board sensors : a feasibility study
RIVA, GIACOMO
2014/2015
Abstract
The main area of research of this work is the diagnostics of the rail infrastructure, bridges in particular. The purpose of the dissertation is, first of all, to formulate a diagnostic method which uses the on-board acceleration signals to localise the damaged section. Secondly, the goal is to determine the most relevant variables of the problem and to analyse to which extent they affect the effectiveness of the diagnostic method. The time response of the bridge has been calculated with a Matlab script for finite element analysis. The bridge-vehicle interaction has been modelled with increasing complexity: at first a single point force is considered to represent an axle; then the whole carriage is considered as a sequence of four point forces; and at last one bogie was taken into account as a sprung and damped 4 DOF moving system (with rail roughness). The proposed damage localisation method is based upon a comparison between the calculated acceleration signals from the damaged bridge with the ones of the undamaged one. The signals are filtered using a moving mean, to remove the contribution of the first bridge eigenfrequency. It appears that high levels of rail irregularity generate a relevant excitation of the structure, which results in high amplitudes of acceleration, which overwhelm the singularity due to damage. Moreover, the method is not efficient at high speeds, since the duration of the observation is limited. This numerical work should be followed by a field testing campaign to investigate the real applicability of the method and should be compared with other diagnostic techniques found in literature.| File | Dimensione | Formato | |
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2016_04_Riva.pdf
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Descrizione: Testo della tesi
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https://hdl.handle.net/10589/118521