1 |
APPLICATION OF STRUCTURAL MONITORING IN MANAGEMENT DECISIONS FOR LARGE INFRASTRUCTURELevy, Joshua 18 November 2011 (has links)
The traditional bridge evaluation process contains uncertainty that affects management decisions. Numerical models require assumptions regarding structural response, and code load models are inherently conservative to ensure uniform applicability.
This research investigated how structural monitoring could reduce uncertainty in the evaluation and management process. Targeted instrumentation was implemented on the MacKay Bridge. Controlled load testing was conducted to refine an existing numerical model. Long-term monitoring was completed to compare extreme in-situ traffic effects with the Canadian Highway Bridge Design Code. Throughout the project, accuracy of information collected was a priority; deviation from code recommendations requires absolute confidence in the data.
Outputs from controlled testing indicated that the existing numerical model for load distribution and structural response required minimal tuning. Long-term testing indicated that actual load effects are less than code requirements.
Results from this thesis show that structural monitoring can reduce uncertainty in structural evaluation and management decisions for infrastructure.
|
2 |
Contribuição ao desenvolvimento de técnicas de monitoramento remoto para blocos de fundação de edifícios em concreto armado com vistas à durabilidade. / Contribution to the development of techniques to remote monitoring for foundation building blocks in concrete with a view to durability.Araújo Neto, Gilberto Nery de 30 November 2011 (has links)
Durante muito tempo as estruturas de concreto foram consideradas livres de manutenção, ou seja, estruturas quase eternas a menos que fossem sobrecarregadas ou destruídas intencionalmente ou por acidente. Esse pensamento caiu por terra nas últimas décadas quando várias estruturas de concreto começaram a apresentar problemas degradando-se bem mais rápido que o esperado. O monitoramento estrutural nasceu da necessidade de acessar a condição de segurança de uma estrutura de forma mais rápida, precisa e com o benefício de criar uma base de dados sobre a estrutura monitorada. O monitoramento de edifícios ainda é um assunto pouco abordado nas pesquisas e publicações. O alto custo agregado às pontes, viadutos e outras grandes estruturas atraem o interesse de pesquisadores e fabricantes de equipamentos. O problema escolhido como alvo no monitoramento a ser desenvolvido foi a degradação de blocos de fundações em concreto armado com reação álcali-agregado (RAA) pela dificuldade de acesso em inspeções. Uma simulação da expansão causado por RAA em concreto foi desenvolvida para experimentos com sensores e técnicas de monitoramento de fundações. No experimento foram testadas aplicações de strain gauges na armadura, na superfície através de um long gauge adaptado e LVDTs (linear variable differential transformer) aplicados na superfície. A ancoragem dos long gauges não suportou o esforço, impedindo a correta avaliação do sensor. Os LVDTs têm grande potencial para acompanhar o desenvolvimento de fissuras, mas sofrem depois de alguma expansão, pois se desalinham com a superfície do concreto. Os strain gauges aplicados na armadura mostraram boa relação com a expansão medida e têm grande potencial no monitoramento. O processo de decisão e projeto do monitoramento para os blocos é explicado e definido. Uma proposta de aplicação do conceito de estrutura tolerante a dano aos blocos de fundação com RAA é dada para otimização de planos de manutenção e intervenções. / For a long time, concrete structures were considered \"maintenance-free\", i.e. quasi eternal, unless they were overloaded or destroyed intentionally or by accident. This thought has been reconsidered in recent decades when several concrete structures began to present problems and degraded much faster than expected. Structural monitoring has been originated from the need to access the safety condition of a structure more quickly, accurately and with the benefit of creating a database of the structure monitored. The high cost related to bridges, overpasses and other large structures still attracts the interest of researchers and equipment manufacturers. However, the monitoring of buildings is still a subject rarely addressed in research and publications. The problem chosen to be addressed in this research is the degradation of reinforced concrete foundation blocks by alkali-aggregate reaction (AAR) due to difficult access during inspections and unpredictable development of the problem. A review on the sensors available on the market and on monitoring techniques used in other structures with the problem was undertaken. A simulation of the AAR`s expansion in concrete has been developed for an experiment with sensors and monitoring techniques of foundations. In this experiment, strain gauges were applied on the reinforcing bars and adapted on a long gauge on the surface. LVDTs (linear variable differential transformer) were also applied on the surface. The anchoring of the long gauges did not support the applied tension, preventing a correct evaluation of the sensor. LVDTs have great potential to monitor the development of cracks, but after the concrete suffering some expansion, they get misaligned with the surface. The strain gauges used in the armor showed a good relation with the expansion and have great potential in monitoring. The whole decision and design process for the structural health monitoring (SHM) for AAR attacked foundation blocks is explained and the project is defined. A proposal of a damage-tolerant approach for the block is given for optimization of maintenance and interventions.
|
3 |
Contribuição ao desenvolvimento de técnicas de monitoramento remoto para blocos de fundação de edifícios em concreto armado com vistas à durabilidade. / Contribution to the development of techniques to remote monitoring for foundation building blocks in concrete with a view to durability.Gilberto Nery de Araújo Neto 30 November 2011 (has links)
Durante muito tempo as estruturas de concreto foram consideradas livres de manutenção, ou seja, estruturas quase eternas a menos que fossem sobrecarregadas ou destruídas intencionalmente ou por acidente. Esse pensamento caiu por terra nas últimas décadas quando várias estruturas de concreto começaram a apresentar problemas degradando-se bem mais rápido que o esperado. O monitoramento estrutural nasceu da necessidade de acessar a condição de segurança de uma estrutura de forma mais rápida, precisa e com o benefício de criar uma base de dados sobre a estrutura monitorada. O monitoramento de edifícios ainda é um assunto pouco abordado nas pesquisas e publicações. O alto custo agregado às pontes, viadutos e outras grandes estruturas atraem o interesse de pesquisadores e fabricantes de equipamentos. O problema escolhido como alvo no monitoramento a ser desenvolvido foi a degradação de blocos de fundações em concreto armado com reação álcali-agregado (RAA) pela dificuldade de acesso em inspeções. Uma simulação da expansão causado por RAA em concreto foi desenvolvida para experimentos com sensores e técnicas de monitoramento de fundações. No experimento foram testadas aplicações de strain gauges na armadura, na superfície através de um long gauge adaptado e LVDTs (linear variable differential transformer) aplicados na superfície. A ancoragem dos long gauges não suportou o esforço, impedindo a correta avaliação do sensor. Os LVDTs têm grande potencial para acompanhar o desenvolvimento de fissuras, mas sofrem depois de alguma expansão, pois se desalinham com a superfície do concreto. Os strain gauges aplicados na armadura mostraram boa relação com a expansão medida e têm grande potencial no monitoramento. O processo de decisão e projeto do monitoramento para os blocos é explicado e definido. Uma proposta de aplicação do conceito de estrutura tolerante a dano aos blocos de fundação com RAA é dada para otimização de planos de manutenção e intervenções. / For a long time, concrete structures were considered \"maintenance-free\", i.e. quasi eternal, unless they were overloaded or destroyed intentionally or by accident. This thought has been reconsidered in recent decades when several concrete structures began to present problems and degraded much faster than expected. Structural monitoring has been originated from the need to access the safety condition of a structure more quickly, accurately and with the benefit of creating a database of the structure monitored. The high cost related to bridges, overpasses and other large structures still attracts the interest of researchers and equipment manufacturers. However, the monitoring of buildings is still a subject rarely addressed in research and publications. The problem chosen to be addressed in this research is the degradation of reinforced concrete foundation blocks by alkali-aggregate reaction (AAR) due to difficult access during inspections and unpredictable development of the problem. A review on the sensors available on the market and on monitoring techniques used in other structures with the problem was undertaken. A simulation of the AAR`s expansion in concrete has been developed for an experiment with sensors and monitoring techniques of foundations. In this experiment, strain gauges were applied on the reinforcing bars and adapted on a long gauge on the surface. LVDTs (linear variable differential transformer) were also applied on the surface. The anchoring of the long gauges did not support the applied tension, preventing a correct evaluation of the sensor. LVDTs have great potential to monitor the development of cracks, but after the concrete suffering some expansion, they get misaligned with the surface. The strain gauges used in the armor showed a good relation with the expansion and have great potential in monitoring. The whole decision and design process for the structural health monitoring (SHM) for AAR attacked foundation blocks is explained and the project is defined. A proposal of a damage-tolerant approach for the block is given for optimization of maintenance and interventions.
|
4 |
QUALIFYING THE COCKPIT VOICE RECORDER AS AN INSTRUMENTATION RECORDER AND AIRCRAFT STRUCTURAL MONITORING INSTRUMENTRohre, Stuart M. 10 1900 (has links)
International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California / A novel concept using the cockpit voice recorder (CVR) as a structural vibration
recording device, to aid in structural health monitoring of commercial and military aircraft,
is outlined. The unused cables in the CVR wiring harness act as “latent transducers” that
respond to structural vibrations, generating vibration signals, which the CVR records.
Postprocessing of such data can provide clues to problem areas or changes in the
signature of the aircraft. The standards which the CVR must meet to qualify as a
instrumentation-quality recorder are discussed and the steps required to assure
compliance are outlined.
|
5 |
Desenvolvimento de transdutor de modo SH0 omnidirecional utilizando arranjo de cerâmicas piezoelétricasMenin, Paulo Dambros January 2017 (has links)
A utilização de ondas guiadas em técnicas de monitoramento de integridade estrutural tem se mostrado uma alternativa interessante para economia de tempo e de custos de operação. Técnicas com ondas guiadas apresentam a característica de monitorar trechos extensos de uma estrutura a partir de um único ponto de acesso, permitindo a inspeção de partes remotas e de difícil acesso. Entre os modos fundamentais de propagação de ondas guiadas em chapas, o modo SH0 possui a vantagem de não ser dispersivo, além de sofrer menores atenuações ao se propagar em superfícies em contato com fluidos. Neste trabalho é proposto um modelo de transdutor do modo SH0 de forma omnidirecional em uma chapa de aço utilizando um arranjo com cerâmicas piezoelétricas, que permita inspecionar determinada área de um componente através de um único modo de propagação. Para caracterizar e compreender o comportamento da resposta obtida foram realizadas simulações numéricas parametrizando características do modelo proposto, como o número de elementos piezoelétricos e dimensões geométricas dos componentes do transdutor. Para validação dos resultados do modelo numérico foram construídos modelos experimentais do transdutor, os quais foram instalados sobre uma chapa de aço de 2mm de espessura para verificação dos modos de propagação emitidos. Avaliando a relação entre intensidades de cada modo emitido e a qualidade da emissão de SH0 foi possível identificar as frequências que apresentaram resposta com a característica desejada. Também foi verificado o comportamento dos transdutores construídos ao serem excitados por ondas propagando na chapa, avaliando a sua utilização também como receptores. / The use of guided waves in structural health monitoring techniques has already proved to be an interesting alternative to reduce inspection time and overall operational costs. Guided waves techniques enable monitoring large structures from one single access point, allowing the inspection of distant and hard access parts. Among the fundamental propagation modes of guided waves in plates, the SH0 mode has the advantage of being non dispersive, as well as being subject to less attenuation when propagating through surfaces in contact with fluids. In this work, it is proposed one omnidirectional SH0 mode transducer in a steel plate using a piezoelectric ceramic array, which allows inspecting a component area through a single propagation mode. Numeric simulations parameterizating features of the transducer, such as the number of piezoelectric elements and the geometric dimensions of the transducer’s components, were developed to characterize and investigate the effect on the output response. To validate the numeric simulation results, experimental models of the transducer were built, which were installed on a 2mm thick steel plate to verify the generated propagation modes. The analysis of the relation between the intensity of each mode generated in the plate and the emission quality of the SH0 mode allowed the identification of frequencies that presented the most desirable response characteristics. The behavior of the built transducers was also studied when they were excited by waves propagating through the plate, evaluating the use of the transducers as signal receptors.
|
6 |
Τεκμηρίωση δυνατότητας μετρήσεων ταλαντώσεων δύσκαμπτων κατασκευών με GPS και ρομποτικό θεοδόλιχο (RTS) : πειραματική, αναλυτική προσέγγιση και εφαρμογέςΨιμούλης, Παναγιώτης 20 October 2009 (has links)
Το βασικό αποτέλεσμα της παρούσας διατριβής η οποία εντάσσεται στην έρευνα που εκπονείται στο Εργαστήριο Γεωδαισίας και Γεωδαιτικών Εφαρμογών του Τμήματος Πολιτικών Μηχανικών του Πανεπιστημίου Πατρών είναι ότι το GPS και ο ρομποτικός θεοδόλιχος (RTS), και κυρίως ο συνδυασμός τους, έχουν τη δυνατότητα μέτρησης ταλαντώσεων όχι μόνο μέχρι 1 Hz, όπως τεκμηριώνεται βιβλιογραφικά, αλλά ενός πολύ μεγαλύτερου φάσματος (μέχρι και 4Hz), ως προς ανεξάρτητο σύστημα αναφοράς της μελετούμενης κατασκευής. Η δυνατότητα αυτή καλύπτει μια σημαντική ανάγκη της σύγχρονης μηχανικής στον τομέα του ελέγχου της δομικής ακεραιότητας (Structural Health Monitoring) των κατασκευών (A’ μέρος της Διατριβής). Τα συμπεράσματα αυτά προέκυψαν με βάση πειράματα και αναλυτική επεξεργασία των δεδομένων των πειραμάτων (B μέρος της Διατριβής) και εφαρμογή της τεχνικής σε δύο δύσκαμπτες μεταλλικές γέφυρες (Γ και Δ μέρη της Διατριβής).
Ειδικότερα, με βάση μεγάλο (>350) αριθμό πειραμάτων σε συσκευή προκαθορισμένων γραμμικών ταλαντώσεων, έγινε ταυτόχρονη καταγραφή ταλαντώσεων γνωστού εύρους και συχνότητας από γεωδαιτικούς δέκτες GPS και RTS, με το τελευταίο να έχει αναβαθμιστεί για λεπτομερέστερη χρονική ανάλυση των καταγραφών. Εν συνεχεία συγκρίθηκαν οι εκτιμήσεις εύρους και συχνότητας που προέκυψαν από την ανάλυση των καταγραφών των GPS, RTS με τα πραγματικά προκαθορισμένα μεγέθη των ταλαντώσεων. Η επεξεργασία και αξιολόγηση των δεδομένων επέτρεψε να εκτιμηθούν τα όρια εφαρμογής κάθε οργάνου GPS/RTS και η απόδοσή τους.
Η ανάλυση βασίστηκε σε στατιστικές μεθόδους (φίλτρα) και ειδικές φασματικές μεθόδους ανάλυσης στο πεδίο συχνοτήτων και χρόνου που επιτρέπουν επεξεργασία χρονικά ανισαπέχοντων και περιορισμένων σε πλήθος δεδομένων (σε αντίθεση με την FFT), αλλά και υπέρβαση των περιορισμών των οργάνων, όπως αστάθεια ρυθμού δειγματοληψίας (‘jitter’) και απώλεια κύκλων ταλάντωσης (“clipping”) του RTS.
Διαπιστώθηκε ότι κυρίως σε υψίσυχνες ταλαντώσεις το GPS προσδιορίζει την κυματομορφή και τη συχνότητα των ταλαντώσεων ενώ το RTS προσδιορίζει με μεγαλύτερη ακρίβεια το εύρος ταλάντωσης. Ο συνδυασμός των δύο οργάνων επιφέρει το πλήρη προσδιορισμό των χαρακτηριστικών (εύρος και συχνότητα) της ταλάντωσης.
Η όλη τεχνική εφαρμόστηκε σε δύο σχετικά δύσκαμπτες γέφυρες. Πρώτον, μεταλλική πεζογέφυρα μήκους ~60m στη Λεωφ. Κηφισού στην Αθήνα με προβλεπόμενο εύρος μετακίνησης <30mm και ιδιοσυχνότητα >3Hz. Με χρήση υπερστατικού καταγραφικού δικτύου GPS, RTS κατεγράφησαν οι μετακινήσεις του μέσου του ανοίγματος λόγω περιοδικής διέγερσης από ομάδα ανθρώπων. Από την ανάλυση των καταγραφών των οργάνων και το συνδυασμό των αποτελεσμάτων τους προέκυψε ότι η απόκριση της γέφυρας ήταν 4-6mm και οι συχνότητες που εμφανίστηκαν ήταν 1, 2.3 και 4.3 Hz (κύρια ιδιοσυχνότητα), συμφωνόντας και με καταγραφές επιταχυνσιογράφου που χρησιμοποιήθηκε κατά τη διάρκεια των πειραμάτων.
Η δεύτερη περίπτωση εφαρμογής της μεθόδου αποτελεί η καταγραφή της κίνησης ενός από τα 7 ανοίγματα της σιδηροδρομικής γέφυρας του Γοργοποτάμου. Χρησιμοποιήθηκε υπερστατικό καταγραφικό δίκτυο GPS, RTS για την καταγραφή των μετακινήσεων του άκρου και μέσου ανοίγματος κατά τη διέλευση συρμών. Οι μετρήσεις του GPS επηρεάστηκαν από φαινόμενο πολυανάκλασης κατά τη διάρκεια της διέλευσης του τραίνου, οδηγώντας σε κυματομορφή η οποία χαρακτηρίζεται από σφάλμα κλίμακας το οποίο τεκμηριώθηκε από επεξεργασία των δεδομένων και πειράματα. Από τη συνολική ανάλυση των δεδομένων των δύο οργάνων και το συνδυασμό τους προέκυψε ότι η μετακίνηση της γέφυρας στη διέλευση του τραίνου ήταν ~6-7mm και η κύρια ιδιοσυχνότητα της ~3.1-3.2Hz. Επιπλέον, διαπιστώθηκε ότι η κυματομορφή της απόκρισης παρουσιάζει διακριτή μορφή που εκφράζει το πλήθος των βαγονιών του συρμού.
Το τελικό συμπέρασμα της διατριβής (Μέρος Ε) είναι ότι η τεκμηρίωση των νέων ορίων εφαρμογής και ποιότητας των καταγραφών GPS, RTS (>5mm, <5Hz) δεν επιτρέπει τη χρήση τους μόνο σε εύκαμπτες κατασκευές (καλωδιωτές γέφυρες, κλπ.) όπως εκτιμάτο μέχρι πρόσφατα, αλλά και σε πιο δύσκαμπτες κατασκευές (δικτυωτές γέφυρες, κλπ.), κάνοντας αυτά πολύτιμο εργαλείο στον έλεγχο της δομικής ακεραιότητας (Structural Health Monitoring) ευρέως τύπου κατασκευών.
Η όλη έρευνα στόχευσε σε όργανα, λογισμικά και τεχνικές προσιτές σε ευρύ φάσμα ερευνητών, ώστε η μέθοδος να μην περιορίζεται σε μερικούς ειδικούς, αλλά εκτιμάται ότι τυχόν χρήση βελτιωμένων λογισμικών, οργάνων εξελιγμένων προδιαγραφών και ειδικών υπολογιστικών τεχνικών θα επιτρέψει στο εγγύς μέλλον βελτίωση της απόδοσης των δύο γεωδαιτικών οργάνων. / The main topic of this dissertation is the assessment of the performance of GPS and RTS in monitoring movements of rigid structures, such as those with main modal frequencies higher than 2Hz. This study was based on experiments of computer-controlled oscillations which were recorded simultaneously by GPS and RTS. These experiments proved that GPS was accurate in definition of the waveform of the oscillation and its frequency, while RTS was more accurate in amplitude definition.
The analysis of GPS, RTS data were based on adaptive filter and spectral analysis technique developed in the Geodesy Lab. of PAtras University, which make possible to overcome data problems such as the gaps of GPS data and the jitter and clipping effect of RTS data. In the second part of this study, GPS and RTS and the developed methodology are adopted for the definition of the dynamic characteristics of two rigid structures a steel pedestrian bridge and a steel train bridge. Based on the combination of the results of GPS and RTS data the main vertical movement and the main modal frequencies of the structures were defined, proving that the combination of these instruments and by using appropriate the definition of the dynamic characteristics even of rigid structures is possible
|
7 |
Instrumented Monitoring And Dynamic Testing Of Metu Cable Stayed Pedestrian Bridge And Comparisons Against The Analytical Model SimulationsOzerkan, Taner 01 July 2005 (has links) (PDF)
This study includes structural instrumentation and monitoring of a 48.5 meters long cable-stayed pedestrian bridge located on EskiSehir road near METU campus. The objectives of the study are (1) to monitor the bridge responses during erection and operation stages so that the strain changes are determined during important events such as transportation, lifting, cabling, mid-support removal, slab concrete pouring and tile placement, (2) to determine existing cable forces using vibration frequencies, and (3) comparison of the experimental and analytical results for model updating.
A total of 10 vibrating wire type strain gages were used for strain readings in steel members. The readings are taken at various stages of construction at every 10 to 30 minutes intervals. The bridge responses were monitored about three months and large strain changes in the order of 300 to 500 micro-strain were recorded during important events (e.g., transportation, lifting, cabling, mid-support removal, deck cover placement).
The deck and tower natural vibration frequency measurements are conducted in two main directions. Two different FE models are constructed using two levels of complexity. FEM analysis results are compared against measured natural frequencies of the bridge and tower.
Simplistic analytical model is modified to include temporary support removal in order to perform staged construction simulation and investigate cable force variations. Actual cable tensile forces are obtained using measured cable natural vibration frequencies. The cable frequencies are measured using a CR10X data logger and a PCB 393C accelerometer. Existing cable forces are compared against analytical simulations and symmetrically placed cables
|
8 |
Desenvolvimento de transdutor de modo SH0 omnidirecional utilizando arranjo de cerâmicas piezoelétricasMenin, Paulo Dambros January 2017 (has links)
A utilização de ondas guiadas em técnicas de monitoramento de integridade estrutural tem se mostrado uma alternativa interessante para economia de tempo e de custos de operação. Técnicas com ondas guiadas apresentam a característica de monitorar trechos extensos de uma estrutura a partir de um único ponto de acesso, permitindo a inspeção de partes remotas e de difícil acesso. Entre os modos fundamentais de propagação de ondas guiadas em chapas, o modo SH0 possui a vantagem de não ser dispersivo, além de sofrer menores atenuações ao se propagar em superfícies em contato com fluidos. Neste trabalho é proposto um modelo de transdutor do modo SH0 de forma omnidirecional em uma chapa de aço utilizando um arranjo com cerâmicas piezoelétricas, que permita inspecionar determinada área de um componente através de um único modo de propagação. Para caracterizar e compreender o comportamento da resposta obtida foram realizadas simulações numéricas parametrizando características do modelo proposto, como o número de elementos piezoelétricos e dimensões geométricas dos componentes do transdutor. Para validação dos resultados do modelo numérico foram construídos modelos experimentais do transdutor, os quais foram instalados sobre uma chapa de aço de 2mm de espessura para verificação dos modos de propagação emitidos. Avaliando a relação entre intensidades de cada modo emitido e a qualidade da emissão de SH0 foi possível identificar as frequências que apresentaram resposta com a característica desejada. Também foi verificado o comportamento dos transdutores construídos ao serem excitados por ondas propagando na chapa, avaliando a sua utilização também como receptores. / The use of guided waves in structural health monitoring techniques has already proved to be an interesting alternative to reduce inspection time and overall operational costs. Guided waves techniques enable monitoring large structures from one single access point, allowing the inspection of distant and hard access parts. Among the fundamental propagation modes of guided waves in plates, the SH0 mode has the advantage of being non dispersive, as well as being subject to less attenuation when propagating through surfaces in contact with fluids. In this work, it is proposed one omnidirectional SH0 mode transducer in a steel plate using a piezoelectric ceramic array, which allows inspecting a component area through a single propagation mode. Numeric simulations parameterizating features of the transducer, such as the number of piezoelectric elements and the geometric dimensions of the transducer’s components, were developed to characterize and investigate the effect on the output response. To validate the numeric simulation results, experimental models of the transducer were built, which were installed on a 2mm thick steel plate to verify the generated propagation modes. The analysis of the relation between the intensity of each mode generated in the plate and the emission quality of the SH0 mode allowed the identification of frequencies that presented the most desirable response characteristics. The behavior of the built transducers was also studied when they were excited by waves propagating through the plate, evaluating the use of the transducers as signal receptors.
|
9 |
Desenvolvimento de transdutor de modo SH0 omnidirecional utilizando arranjo de cerâmicas piezoelétricasMenin, Paulo Dambros January 2017 (has links)
A utilização de ondas guiadas em técnicas de monitoramento de integridade estrutural tem se mostrado uma alternativa interessante para economia de tempo e de custos de operação. Técnicas com ondas guiadas apresentam a característica de monitorar trechos extensos de uma estrutura a partir de um único ponto de acesso, permitindo a inspeção de partes remotas e de difícil acesso. Entre os modos fundamentais de propagação de ondas guiadas em chapas, o modo SH0 possui a vantagem de não ser dispersivo, além de sofrer menores atenuações ao se propagar em superfícies em contato com fluidos. Neste trabalho é proposto um modelo de transdutor do modo SH0 de forma omnidirecional em uma chapa de aço utilizando um arranjo com cerâmicas piezoelétricas, que permita inspecionar determinada área de um componente através de um único modo de propagação. Para caracterizar e compreender o comportamento da resposta obtida foram realizadas simulações numéricas parametrizando características do modelo proposto, como o número de elementos piezoelétricos e dimensões geométricas dos componentes do transdutor. Para validação dos resultados do modelo numérico foram construídos modelos experimentais do transdutor, os quais foram instalados sobre uma chapa de aço de 2mm de espessura para verificação dos modos de propagação emitidos. Avaliando a relação entre intensidades de cada modo emitido e a qualidade da emissão de SH0 foi possível identificar as frequências que apresentaram resposta com a característica desejada. Também foi verificado o comportamento dos transdutores construídos ao serem excitados por ondas propagando na chapa, avaliando a sua utilização também como receptores. / The use of guided waves in structural health monitoring techniques has already proved to be an interesting alternative to reduce inspection time and overall operational costs. Guided waves techniques enable monitoring large structures from one single access point, allowing the inspection of distant and hard access parts. Among the fundamental propagation modes of guided waves in plates, the SH0 mode has the advantage of being non dispersive, as well as being subject to less attenuation when propagating through surfaces in contact with fluids. In this work, it is proposed one omnidirectional SH0 mode transducer in a steel plate using a piezoelectric ceramic array, which allows inspecting a component area through a single propagation mode. Numeric simulations parameterizating features of the transducer, such as the number of piezoelectric elements and the geometric dimensions of the transducer’s components, were developed to characterize and investigate the effect on the output response. To validate the numeric simulation results, experimental models of the transducer were built, which were installed on a 2mm thick steel plate to verify the generated propagation modes. The analysis of the relation between the intensity of each mode generated in the plate and the emission quality of the SH0 mode allowed the identification of frequencies that presented the most desirable response characteristics. The behavior of the built transducers was also studied when they were excited by waves propagating through the plate, evaluating the use of the transducers as signal receptors.
|
10 |
Evaluation of AASHTO design specifications for cast-in-place continuous bridge deck using remote sensing techniqueMehranipornejad, Ebrahim 01 June 2006 (has links)
This research project concerns the construction, testing, and remote health monitoring of the first smart bridge structure in Florida, the East Bay bridge in Gibsonton, Hillsborough County. The East Bay Bridge is a four span, continuous, deck-type structure with a total length of 120' and width of 55'. The superstructure consists of an 18'' cast-in-place reinforced concrete slab, and is supported on pre-stressed pile bents, each consisting of 5 piles. The smart sensors used for remote health monitoring are the newly emerged Fabry --Perot (FP) Fiber Optic Sensors, and are both surface-mounted and embedded in the concrete deck.Static and Dynamic testing of the bridge were performed using loaded SU-4 trucks, and a finite element model for the bridge was developed for the test cases using commercial software packages. In addition, the smart sensors were connected to a data acquisition system permanently installed on-site. This system could be accessed through regular phone lin
es, which permits the evaluation of the bridge behavior under live traffic loads.Currently, these live structural data under traffic loading are transmitted to Hillsborough County's bridge maintenance office to assist in the health evaluation and maintenance of the bridge.AASHTO LRFD Design Code has been investigated using analytical and laboratory test but no attempt has been made to verify its relative outlook with respect to Allowable Strength Design (ASD) and AASHTO Standard Specifications (LFD) in a real field test. The likely reason for could have been the lack of accurate and reliable sensing systems.The data collected as well as the analytical studies through out this research, suggest that current LRFD design specifications for deck-type bridges are conservative. The technology developed under this work will enable practical, cost-effective, and reliable systematic maintenance of bridge structures, and the study will provide a unique opportunity for future growth of this tech
nology in the state of Florida and in other states and finally, long term collected data can be used to keep the design codes in check.
|
Page generated in 0.0831 seconds