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This thesis describes new signal processing techniques applicable to miniature low finesse Fabry-Perot interferometric sensors. The principle of operation behind the techniques presented resides in the use of the axial modes from a single multimode laser diode to produce a series of phrase shifted interferometric outputs in conjunction with the path imbalance of the sensor microactivity.

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A novel accelerometer based on light modulation has been designed and a prototype device manufactured. The device utilises the change in refractive index brought about by stress induced by the applied vibration. A detailed mathematical analysis of several feasible sensing designs has been performed to aid the design process. A mathematical model has been developed to assess the performance characteristics of the light modulated accelerometer the results of which were also used as a design tool. The prototype accelerometer was tested, from 1 g to 50 g between frequencies of 25 Hz to 2000 Hz, on a vibration system under three modulation schemes. The acceleration response of the device was seen to be linear over the testing range whilst the frequency response dropped off initially and levelled off at approximately 1 kHz. An experimental accelerometer was also assembled on the vibration table so that various materials could easily be tested without having to undergo precise machining. The acceleration and frequency responses showed similar behaviour to those obtained with the prototype accelerometer. However, the actual response levels varied with each material. To aid in the development of the accelerometer the stress-optic and thermo-optic coefficients have been determined for a range of polymeric materials. The stress optic coefficient was determined for polycarbonate, polymethyl methacrylate, polvinyl chloride and araldite epoxy resin using a circular polariscope and two interferometer configurations up to the yield stress of the materials tested. Each material showed a constant coefficient over the testing range. The results obtained using each technique were in good agreement with each other and the limited literature data available. The thermal variation of refractive index was also determined for the same materials. The Abbe refractometer was used for the determination between 5 and 140°C using five wavelength sources and two interferometer configurations using a HeNe laser from -50°C to approximately 30° above the glass transition temperatures. The change in index was found to be linear over the temperature range tested. However, at the glass transition temperature a change in gradient was observed with each material. Two simple mathematical relationships were used to predict the thermo-optic coefficient. These gave values reasonably close to those obtained in experiment.

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Structural Health Monitoring (SHM) with emerging technologies like e.g. fibre optic sensors, lasers, radars, acoustic emission and Micro Electro Mechanical Systems (MEMS) made an entrance into the civil engineering field in last decades. Expansion of new technologies together with development in data communication benefited for rapid development. The author has been doing research as well as working with SHM and related tasks nearly a decade. Both theoretical knowledge and practical experience are gained in this constantly developing field. This doctoral thesis presents lessons learned in SHM and sensory technologies when monitoring civil engineering structures, mostly bridges. Nevertheless, these techniques can also be used in most applications related to civil engineering like dams, high rise buildings, off-shore platforms, pipelines, harbour structures and historical monuments. Emerging and established technologies are presented, discussed and examples are given based on the experience achieved. A special care is given to Fibre Optic Sensor (FOS) technology and its latest approach. Results from crack detection testing, long-term monitoring, and sensor comparison and installation procedure are highlighted. The important subjects around sensory technology and SHM are discussed based on the author's experience and recommendations are given. Applied research with empirical and experimental methods was carried out. A state-of-the art-review of SHM started the process but extensive literature studies were done continuously along the years in order to keep the knowledge up to date. Several SHM cases, both small and large scale, were carried out including sensor selection, installation planning, physical installation, data acquisition set-up, testing, monitoring, documentation and reporting. One case study also included modification and improvement of designed system and physical repair of sensors as well as two Site Acceptance Tests (SATs) and the novel crack detection system testing. Temporary measuring and testing also took place and numerous Structural Health Monitoring Systems (SHMSs) were designed for new bridges. The observed and measured data/phenomena were documented and analysed.  Engineers, researchers and owners of structures are given an essential implement in managing and maintaining structures. Long-term effects like shrinkage and creep in pre-stressed segmental build bridges were studied. Many studies show that existing model codes are not so good to predict these long-term effects. The results gained from the research study with New Årsta Railway Bridge are biased be the fact that our structure is indeed special. Anyhow, the results can be compared to other similar structures and adequately used for the maintenance planning for the case study. A long-term effect like fatigue in steel structures is a serious issue that may lead to structural collapse. Novel crack detection and localisation system, based on development on crack identification algorithm implemented in DiTeSt system and SMARTape delamination mechanism, was developed, tested and implemented. Additionally, new methods and procedures in installing, testing, modifying and improving the installed system were developed. There are no common procedures how to present the existing FOS techniques. It is difficult for an inexperienced person to judge and compare different systems. Experience gained when working with Fibre Optic Sensors (FOS) is collected and presented. The purpose is, firstly to give advice when judging different systems and secondly, to promote for more standardised way to present technical requirements. Furthermore, there is need to regulate the vocabulary in the field. Finally, the general accumulated experience is gathered. It is essential to understand the complexity of the subject in order to make use of it. General trends and development are compared for different applications. As the area of research is wide, some chosen, specific issues are analysed on a more detailed level. Conclusions are drawn and recommendations are given, both specific and more general. SHMS for a complex structure requires numerous parameters to be measured. Combination of several techniques will enable all required measurements to be taken. In addition, experienced specialists need to work in collaboration with structural engineers in order to provide high-quality systems that complete the technical requirement. Smaller amount of sensors with proper data analysis is better than a complicated system with numerous sensors but with poor analysis. Basic education and continuous update for people working with emerging technologies are also obligatory. A lot of capital can be saved if more straightforward communication and international collaboration are established: not only the advances but also the experienced problems and malfunctions need to be highlighted and discussed in order not to be repeated. Quality assurance issues need to be optimized in order to provide high quality SHMSs. Nevertheless, our structures are aging and we can be sure that the future for sensory technologies and SHM is promising. The final conclusion is that an expert in SHM field needs wide education, understanding, experience, practical sense, curiosity and preferably investigational mind in order to solve the problems that are faced out when working with emerging technologies in the real world applications.  The human factor, to be able to bind good relationship with workmanship cannot be neglected either. There is also need to be constantly updated as the field itself is in continuous development. / QC 20111117 / SHMS of the New Årsta Railway Bridge

Aufgrund der Altersstruktur der Brücken in Deutschland und des überproportional steigenden Schwerlastverkehrs werden umfängliche Erhaltungsmaßnahmen zur Aufrechterhaltung des Infrastrukturnetzes erforderlich. Zur Dynamisierung der Erhaltungsstrategie werden vermehrt kontinuierliche Bauwerksmessungen zur Überwachung und Beurteilung des Bauwerkszustands eingesetzt. Weiterentwicklungen in der Leistungsfähigkeit hochauflösender faseroptischer Sensoren bieten neue messtechnische Möglichkeiten für die großflächige (permanente) Bauwerksüberwachung. Der Beitrag beleuchtet die Potentiale hochauflösender faseroptischer Sensoren zur Zustandsüberwachung von Bestandsbrücken. In einem Pilotprojekt an einer spannungsrisskorrosionsgefährdeten Spannbetonbrücke wurden bzw. werden derzeit faseroptische Sensoren für eine permanente Überwachung installiert und sukzessive in Betrieb genommen. Die Einsatzmöglichkeiten als Dauermonitoringsystem werden anhand der bisherigen Erfahrungen und Ergebnisse demonstriert.

Aufgrund der Möglichkeit, kontinuierlich Dehnungen messen zu können, bieten verteilte faseroptische Sensoren (DFOS) sowohl im Neubau als auch im Bestand enormes Potential im Bereich des Bauwerksmonitorings. Im Beitrag werden Belastungsversuche an einem alten Brückenträger des Typs BT 500 N bis an den Grenzzustand der Tragfähigkeit vorgestellt. Die mittels DFOS gemessenen Bauteildehnungen und ermittelten Rissbreiten werden mit einer photogrammetrischen Messung (DIC) verglichen. Die Potentiale beider Messtechniken werden bei kleinen und großen Dehnungsniveaus gegenübergestellt. Aufgrund der erreichbaren Messlänge von bis zu 100 m und der hohen Ortsauflösung erweisen sich DFOS als prädestiniert für das Monitoring von Bauwerken. Existierende Herausforderungen im Bereich großer Dehnungen und Rissbreiten werden diskutiert.

To better manage deteriorating infrastructure, quantitative data about the performance of infrastructure assets is required. Rayleigh based distributed fibre optic strain sensing (FOS) is a technology that has the potential to offer this type of data and unlike traditional strain sensors it can measure the strain along the full length of the structure. A series of experiments were undertaken to develop installation techniques and evaluate sensor accuracy for typical civil engineering materials: steel, concrete and reinforced concrete. The results of these experiments showed that the choice of sensing fibre and adhesive was dependent on the material being monitored. When the sensing fibre and adhesive are chosen correctly, the Rayleigh system can provide the same accuracy as a strain gauge for steel and concrete, and useful measurements can be obtained even in areas of concrete cracking. The FOS technique was utilized to determine whether distributed strain measurements could be used to detect and quantify localized deterioration of the steel reinforcement (localized area reductions of 0-30%) at service loads. A series of specimens was tested, the sensing system was able to detect the presence of localized deterioration with embedded nylon and polyimide fibres, but the nylon fibre cannot quantify large strain gradients due to slip within the sensing fibre. The strain profiles gave insights to the failure mechanism occurring in the reinforced concrete specimens. The strain profiles for both test series indicated that the tension reinforcement was acting as a tension tie and the strain profiles suggested the presence of compressive struts indicative of an arching mechanism in the specimens. The Black River bridge in Madoc, Ontario was instrumented with fibre optics sensors to determine whether the use of FOS is both practical and beneficial for reinforced concrete bridge assessment when compared to conventional instrumentation. The FOS showed reasonably good agreement with conventional sensors. The fibre optic strain results are used to calculate curvature, slope and displacement but careful consideration of the boundary conditions is required. The results from the fibre optic sensors can be used to show the bridge load distribution and give insights into the support conditions of the beams. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-08-21 11:56:53.276