Damage Detection Based On Damping Analysis Of Ambient Vibration Data

Enabling an automated, remote and rapid detection of structural damage, sensor-based structural health monitoring is becoming a powerful tool for maintenance of civil engineering structures. In this study, a baseline-free, time-domain damage detection method was developed for concrete structures, which is based on analysis of nonlinear damping from measured structural vibration responses. The efficacy of the proposed method was demonstrated through a large-scale concrete bridge model subjected to different levels of seismic damage caused by shaking table tests. By applying the random decrement signature technique, the proposed method successfully identified, from its ambient vibration responses, nonlinear damping of the bridge associated with the seismic damage. The amount of the nonlinear damping increases as the seismic damage becomes more severe. This paper also compares the damage detection results with those obtained by stiffness-based methods, demonstrating a strong correlation between the increase in nonlinear damping and the decrease in structural stiffness associated with the increase in damage severity

An Experimental Study on the Correlation Between Residual Prestress Force in Pre-Tensioned and Post-Tensioned Concrete Beams and Non-Destructive Tests

The research activity described in this thesis was begun with the aim of investigating the possibilities of applying non-destructive techniques to develop a methodology to assess the presence of damage and the loss in prestressing on prestressed concrete (PRC) beams. The work began with the investigation, in literature, of the methods utilized at present for the assessment of damage in prestressed beams and prestressing cable. Among others, the thesis focused on vibration-based and acoustoelastic techniques, and in particular on the following properties: variations of the fundamental frequency and mode shapes, damping ratio, velocity and attenuation of the ultrasonic signal. Such properties have been rarely analyzed together in literature; moreover, the literature analysis carried out until today showed how further efforts need to be paid to enhance the feasibility of the application of such methods in practice. A wide assessment of the results obtained in literature for vibration based assessment of prestressing losses was carried out. Based on these results, an experimental campaign was set up in the laboratory for Construction Materials Tests of the University of Padova. The tests were carried out on 6 PRC beams, both with bonded and un-bonded tendons, in order to study the effects of the variation of specific parameters on the response of the beams. The three pre-tensioned beams had identical geometrical properties, but with different level of prestressing. The three post-tensioned beams had the peculiarity to allow the prestressing force to be applied manually in laboratory conditions, with the possibility to obtain a wider range of prestressing levels. Moreover, every post-tensioned beam had different cable eccentricity. Static tests were performed until the failure of the beams, and for every load step nondestructive tests were carried out: dynamic free vibration tests and ultrasonic tests. From vibration tests dynamic characteristics were extracted: fundamental frequency, modal damping, mode shapes. The variation of these parameters with respect to damage level and prestressing level was studied. Moreover, also the dependence of ultrasonic parameters, like wave velocity and energy, on damage and prestressing level was emphasized. Particular attention was paid to dissipation phenomena, like modal damping parameters and ultrasonic energy dissipation, which appeared to be extremely sensitive to the formation of cracks and damage. The depth of the study led to the conclusion that there exists an unequivocal relationship between the presence and the entity of the damage and the appearance of such dissipation phenomena. Finally, the effect of the change in the degree of prestressing on nondestructive parameters PRC beams was studied. A method was proposed that make use of only non-destructive tests in order to assess the residual prestressing level of a PRC beam. This methodology could enhance and improve the techniques normally used for the damage detection, enabling a more detailed assessment of the condition of the structure with limited amount of data.L'attività di ricerca descritta in questa tesi è stata avviata con l'obiettivo di studiare le possibilità di applicare tecniche non distruttive valutare la presenza di danno e la perdita di precompressione in travi in calcestruzzo armato precompresso (CAP). Il lavoro è iniziato con l'indagine, in letteratura, dei metodi attualmente utilizzati per la valutazione del danno nelle travi precompresse e nei cavi di precompressione. Tra le tecniche applicabili, la tesi si è concentrata su quelle basate sui metodi vibrazionali e acusto-elastiche, in particolare sullo studio delle seguenti proprietà: variazioni delle frequenze fondamentali e delle forme modali, rapporto di smorzamento, velocità e attenuazione del segnale ultrasonico. Tali proprietà sono state raramente analizzate congiuntamente in letteratura; inoltre, lo studio di letteratura ha mostrato come siano ancora necessari ulteriori sforzi per migliorare l’applicabilità di tali metodi nella pratica. È stata effettuata un'ampia valutazione dei risultati ottenuti negli studi di letteratura per la valutazione delle perdite di precompressione basata sullo studio delle vibrazioni. Sulla base di questi risultati, è stata avviata una campagna sperimentale nel laboratorio per le prove sui materiali da costruzione dell'Università di Padova. I test sono stati condotti su 6 travi in calcestruzzo armato precompresso, sia pretese che post-tese, al fine di studiare gli effetti della variazione di parametri specifici sulla risposta degli elementi strutturali. Le tre travi pretensione avevano proprietà geometriche identiche, ma con un diverso livello di precompressione. Le tre travi post-tese avevano la peculiarità di consentire l'applicazione manuale della forza di precompressione in condizioni di laboratorio, con la possibilità di ottenere una gamma più ampia di livelli di precompressione. Inoltre, ogni trave post-tesa aveva un'eccentricità di cavo diversa. Sono stati eseguiti test statici fino al collasso delle travi e sono stati effettuati test non distruttivi per ogni fase di carico: test dinamici impulsivi e test agli ultrasuoni. Dai risultati delle prove vibrazionali sono state estratte le caratteristiche dinamiche, quali frequenza fondamentale, smorzamento modale, forme modali. È stata studiata la variazione di questi parametri rispetto allo stato di danno e al livello di precompressione. Inoltre, è stata enfatizzata anche la dipendenza di tali fenomeni dai parametri ultrasonici, come la velocità e l'energia delle onde trasmesse. Particolare attenzione è stata prestata ai fenomeni dissipativi, come i parametri di smorzamento modale e la dissipazione di energia dell’onda ultrasonica, che sembrano essere estremamente sensibile alla formazione di fessure e danneggiamenti. L’approfondimento dello studio ha portato alla conclusione che esiste una relazione inequivocabile tra la presenza e l'entità del danno e la comparsa di tali fenomeni dissipativi. Infine, è stato studiato l'effetto del cambiamento nel grado di precompressione sui parametri non distruttivi delle travi in CAP. È stato proposto un metodo che fa utilizzo solamente di test non distruttivi al fine di valutare il livello di precompressione residuo degli elementi in calcestruzzo armato precompresso. Questa metodologia potrebbe portare un miglioramento alle tecniche normalmente utilizzate per il rilevamento del danno, consentendo una valutazione più dettagliata delle condizioni della struttura con una quantità limitata di dati

An Experimental Study on the Correlation Between Residual Prestress Force in Pre-Tensioned and Post-Tensioned Concrete Beams and Non-Destructive Tests

The research activity described in this thesis was begun with the aim of investigating the possibilities of applying non-destructive techniques to develop a methodology to assess the presence of damage and the loss in prestressing on prestressed concrete (PRC) beams. The work began with the investigation, in literature, of the methods utilized at present for the assessment of damage in prestressed beams and prestressing cable. Among others, the thesis focused on vibration-based and acoustoelastic techniques, and in particular on the following properties: variations of the fundamental frequency and mode shapes, damping ratio, velocity and attenuation of the ultrasonic signal. Such properties have been rarely analyzed together in literature; moreover, the literature analysis carried out until today showed how further efforts need to be paid to enhance the feasibility of the application of such methods in practice. A wide assessment of the results obtained in literature for vibration based assessment of prestressing losses was carried out. Based on these results, an experimental campaign was set up in the laboratory for Construction Materials Tests of the University of Padova. The tests were carried out on 6 PRC beams, both with bonded and un-bonded tendons, in order to study the effects of the variation of specific parameters on the response of the beams. The three pre-tensioned beams had identical geometrical properties, but with different level of prestressing. The three post-tensioned beams had the peculiarity to allow the prestressing force to be applied manually in laboratory conditions, with the possibility to obtain a wider range of prestressing levels. Moreover, every post-tensioned beam had different cable eccentricity. Static tests were performed until the failure of the beams, and for every load step nondestructive tests were carried out: dynamic free vibration tests and ultrasonic tests. From vibration tests dynamic characteristics were extracted: fundamental frequency, modal damping, mode shapes. The variation of these parameters with respect to damage level and prestressing level was studied. Moreover, also the dependence of ultrasonic parameters, like wave velocity and energy, on damage and prestressing level was emphasized. Particular attention was paid to dissipation phenomena, like modal damping parameters and ultrasonic energy dissipation, which appeared to be extremely sensitive to the formation of cracks and damage. The depth of the study led to the conclusion that there exists an unequivocal relationship between the presence and the entity of the damage and the appearance of such dissipation phenomena. Finally, the effect of the change in the degree of prestressing on nondestructive parameters PRC beams was studied. A method was proposed that make use of only non-destructive tests in order to assess the residual prestressing level of a PRC beam. This methodology could enhance and improve the techniques normally used for the damage detection, enabling a more detailed assessment of the condition of the structure with limited amount of data

Vibration based structural assessment of the rehabilitation intervention in r.c. segmental bridge

A vibration based structural assessment campaign was carried out on a r.c. segmental bridge in North East Italy. The bridge has a cantilever static scheme, fixed at the top of the piers and with a hinge at the centre of the span. The particular configuration of the hinge consists in a couple of steel elements, each one composed by a tongue and groove joint. Since the year 1960, the hinge was subjected to consumption and degradation, that caused a malfunctioning of the device. An intervention of rehabilitation of the bridge led to a reinforcement of the existing hinges with the coupling of new metallic devices: new tongue and groove hinges were applied, that by one side allow the horizontal displacements and rotation, by the other side strongly reduce the relative vertical displacements of the two parts of the bridge. A dynamic test campaign was set up in order to assess the effectiveness of the intervention. The principal dynamic parameters were calculated and analysed with respect to the intervention that was realized. The tests clearly showed the effectiveness of the intervention, and helped the designer to have a better understanding of the structural behaviour of the bridge

Vibration based structural assessment of the rehabilitation intervention in r.c. segmental bridge

A vibration based structural assessment campaign was carried out on a r.c. segmental bridge in North East Italy. The bridge has a cantilever static scheme, fixed at the top of the piers and with a hinge at the centre of the span. The particular configuration of the hinge consists in a couple of steel elements, each one composed by a tongue and groove joint. Since the year 1960, the hinge was subjected to consumption and degradation, that caused a malfunctioning of the device. An intervention of rehabilitation of the bridge led to a reinforcement of the existing hinges with the coupling of new metallic devices: new tongue and groove hinges were applied, that by one side allow the horizontal displacements and rotation, by the other side strongly reduce the relative vertical displacements of the two parts of the bridge. A dynamic test campaign was set up in order to assess the effectiveness of the intervention. The principal dynamic parameters were calculated and analysed with respect to the intervention that was realized. The tests clearly showed the effectiveness of the intervention, and helped the designer to have a better understanding of the structural behaviour of the bridge

A V1143F mutation in the neuronal-enriched isoform 2 of the PMCA pump is linked with ataxia

The fine regulation of intracellular calcium is fundamental for all eukaryotic cells. In neurons, Ca2+ oscillations govern the synaptic development, the release of neurotransmitters and the expression of several genes. Alterations of Ca2+ homeostasis were found to play a pivotal role in neurodegenerative progression. The maintenance of proper Ca2+ signaling in neurons demands the continuous activity of Ca2+ pumps and exchangers to guarantee physiological cytosolic concentration of the cation. The plasma membrane Ca2+ATPases (PMCA pumps) play a key role in the regulation of Ca2+ handling in selected sub-plasma membrane microdomains. Among the four basic PMCA pump isoforms existing in mammals, isoforms 2 and 3 are particularly enriched in the nervous system. In humans, genetic mutations in the PMCA2 gene in association with cadherin 23 mutations have been linked to hearing loss phenotypes, while those occurring in the PMCA3 gene were associated with X-linked congenital cerebellar ataxias. Here we describe a novel missense mutation (V1143F) in the calmodulin binding domain (CaM-BD) of the PMCA2 protein. The mutant pump was present in a patient showing congenital cerebellar ataxia but no overt signs of deafness, in line with the absence of mutations in the cadherin 23 gene. Biochemical and molecular dynamics studies on the mutated PMCA2 have revealed that the V1143F substitution alters the binding of calmodulin to the CaM-BD leading to impaired Ca2+ ejection