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An important issue in structural health monitoring (SHM) is to develop appropriate algorithms that can explicitly extract meaningful changes in measurements due to structural anomalies, especially damage. However, the effects due to environmental factors, especially temperature variations may produce significant misinterpretations. Consequently, developing solutions to identify the structural anomaly, accounting for temperature influence, from measurements, is crucial and highly anticipated. This paper presents a Temperature-driven Moving Principal Component Analysis method, designated as Td-MPCA, for anomaly detection. The Td-MPCA introduces the idea of blind source separation (BSS) for thermal identification with intent to enhance the performance of Moving Principal Component Analysis (MPCA) for anomaly detection. To achieve this target, temperature-induced strain variations are first investigated and revealed by employing Independent Component Analysis based on maximization non-Gaussianity, also known as Fast ICA. Afterwards, the MPCA is adopted for anomaly detection on the separated temperature-related response. Three case studies are provided in this paper to evaluate the proposed method. The first one is a numerical truss bridge with a simulated 5% stiffness reduction. The results confirm that Td-MPCA is more sensitive than MPCA in detecting anomalies, where the simulated stiffness loss fails to be detected by MPCA. The second case study is on an experimental truss bridge where two damage scenarios are introduced and interpreted. The detection results show that Td-MPCA outperforms MPCA since the damage is identified at the expected time by Td-MPCA but not by MPCA. The third case study is an in-situ curved viaduct in Switzerland. Data acquired during both construction period and normal service period has been used for interpretation. Results demonstrate that Td-MPCA is able to identify the date of change in construction process without any delay when compared with the application of MPCA only.

This work presents an overview of some of the most promising technologies for the structural health monitoring (SHM) of in-service tunnels. The common goal of damage or unusual behaviour detection is best pursued by an integrated approach based on the concurrent deployment of multiple technologies. Typically, traditional SHM systems are installed in problematic or special areas of the tunnels, giving information on conditions and helping manage maintenance. However, these methodologies often have the drawbacks of forcing the interruption of traffic for SHM system installation and monitoring only selected portions. Alternative solutions that would make it possible to keep the tunnel in normal operation and/or to analyse the entire infrastructure development through successive and continuous scanning stages, would be beneficial. In this paper, the authors will briefly review some traditional monitoring technologies for tunnels. Furthermore, the work is aimed at identifying alternative solutions, limiting or avoiding traffic interruptions.

Reinforced concrete structural components such as beams are subject during their service life to different loading conditions that may affect their durability and efficiency. This can reduce the safety level of the structure over time until it degrades completely and reaches its ultimate limit state. In particular, cracking conditions due to tensile conditions can be developed leading to the exposure of the steel reinforcements to the aggression of external agents, such as chlorides. Being able to monitor the development and the evolution of cracking is crucial and this research is aimed at this purpose. In particular, laboratory tests have been performed on reinforced concrete beams equipped with distributed fiber optics sensors to monitor the state of cracking. This technology has been selected because its inherent accuracy and low noise. Furthermore, since technology relies of optical signals, the sensors are not affected by electrical and magnetic noise. They are also resistant to high temperatures and chemically reactive environments. The main objectives of the presented first part of this research are focused on the deformation and temperature assessment after concrete pouring, crack detection, localization and opening quantification.

Miniature optical fiber sensors, based on Fabry-Perot technology, have found numerous applications in both patient monitoring and civil structural monitoring of large and massive infrastructures. Although structural health monitoring and patient monitoring may benefit from the unique advantages of optical fiber sensors (OFS) such as electromagnetic interferences (EMI) immunity, sensor small size and long term reliability, both applications are facing very different realities. This contribution presents the underlying sensing technology, the miniature sensor fabrication technique and numerous application examples in medical and civil engineering-fields. OFS for medical applications are single-point, measuring mainly parameters such as pressure or temperature. In the intra-aortic balloon pumping (IABP) therapy, a miniature OFS can monitor in situ aortic blood pressure to trigger catheter balloon inflation/deflation in counter-pulsation with heartbeats. Similar sensors reliably monitor the intracranial pressure (ICP) of critical care patients, even during surgical intervention or examinations under medical resonance imaging (MRI). Temperature OFS are also the ideal monitoring solution for such harsh environments. The same miniature sensing elements can be packaged differently to allow their use in civil and geotechnical monitoring. In particular, Fabry-Perot optical sensors have been in use for many years as direct replacement of conventional sensors based on the vibrating wire and other electrical technologies. Those sensors are ideal to measure strain, deformation, pressure and temperature in applications subject to strong electromagnetic fields, lighting strikes or requiring long cables. Application examples includes the monitoring of groundwater pressures in tailing dams used for mining applications in Chile, leaks in levees in The Netherlands and displacements in the cryogenically cooled superconducting magnets for ITER project in France.

New and existing tunnels can present structural risks related to surrounding geotechnical and hydrological conditions as well as unknowns related to design assumptions and construction materials. Such risks can materialize through the apparition of abnormal deformations, cracks, water ingress or, in the worse cases, collapse. The localization of such events or their precursor signs is a-priori unknown, so traditional instrumentation in chosen cross-sections is ineffective for damage detection and localization. Regular visual inspection is more effective in terms of detection probability, but is typically limited in terms of temporal intervals between visits. Additionally, tunnels are often difficult to inspect since the access is restricted due to operational reasons. If such structural risks have been recognized in the design phase or have been identified by inspection, installing a distributed fiber optic sensing system allows a permanent monitoring of the tunnel over its whole length. Sensing cables are typically installed longitudinally along the tunnel length at different positions around the section and provide detection and localization or abnormal deformations and settlements, formation or development of cracks and unusual temperatures. This contribution presents the application of distributed optical fiber sensing to the permanent monitoring of a highway, a railway and a penstock tunnel. For each project we provide information about the system design, installation and monitoring results.

Optical fiber sensors can be used advantageously for monitoring dams and levees and to detect and localize damage in them. This technology is relatively new, but in the last 20 years numerous applications have been successfully carried out in dams, dykes and levees worldwide. There are two main usage scenarios for optical fiber sensing technology. Some sensors replace conventional, e.g. vibrating wire, sensors with equivalent optical versions. In this case the main benefits come from their immunity to electromagnetic interference—such as lightning strikes or power lines—and the possibility to use cables of up to several km long to connect the sensors and the readout units. The second main application of optical fiber sensing relies on the use of distributed sensors. Those sensors can measure strain and temperature every meter along a cable that can reach several km in length. This enables detecting and localizing undesired events such as leaks or cracks that produce a local change of strain or temperature. In this chapter we will introduce the different optical fiber sensing technologies and corresponding sensors. Several applications example will illustrate the abovementioned use scenarios.

Uncertainty about the survivability and technological evolution presents its risks when designing the sensors to use on infrastructure health monitoring systems. Fibre optic methods have been available for some time, and are reaching the technological maturity required to provide reliable long-term structural health monitoring solutions. By embedding fibre optic sensors in the structures at construction time, the engineers are able to detect deviations from the structure’s original design and expected dynamics. However, due to the long-term infrastructure’s life span and the relatively new fibre optic techniques, there are very few historical examples to analyse and use as proof for the adequacy of such techniques to the infrastructure’s life-cycle. This study explores the risks and opportunities associated with these technologies through a real case of one of the first Fibre Bragg Grating (FBG) sensorized highway bridge installed in Spain in the year 2000, the «Las Navas» bridge at the A-8 «Autovía del Cantábrico» highway in the north of Spain. The survivability of the fibre optic sensors, after eighteen years of embedded exposure, is compared to the traditional strain gauges solutions and the maintenance challenges they face. And, most importantly, the exciting new opportunities that the new measurement units can offer, are analysed, evaluating the re-purpose capacity of the health monitoring systems fibre optic sensors as sustainable real time operational monitoring systems. The originally designed structural sensors are proved to be useful also to detect, count and classify operational traffic using the infrastructure, by applying machine learning techniques that add another benefit of the use of these type of measurement sensors into the infrastructure’s world. The fibre sensor company SMARTEC and also the R&D H2020-EU.3.4. project RAGTIME (Grant agreement ID: 690660), thanks to which it all started with the first site visit.

This paper will discuss the challenges and solutions required for large scale production of more than 250 000 Fabry-Perot sensors per year, demonstrating that automated production of large-volume fiber optic sensing is now a reality. Medical and industrial applications requiring large volume production are also explored.

This paper illustrates an application of Bayesian logic to monitoring data analysis and structural condition state inference. The case study is a 260 m long cable-stayed bridge spanning the Adige River 10 km north of the town of Trento, Italy. This is a statically indeterminate structure, having a composite steel-concrete deck, supported by 12 stay cables. Structural redundancy, possible relaxation losses and an as-built condition differing from design, suggest that long-term load redistribution between cables can be expected. To monitor load redistribution, the owner decided to install a monitoring system which combines built-on-site elasto-magnetic and fiber-optic sensors. In this note, we discuss a rational way to improve the accuracy of the load estimate from the EM sensors taking advantage of the FOS information. More specifically, we use a multi-sensor Bayesian data fusion approach which combines the information from the two sensing systems with the prior knowledge, including design information and the outcomes of laboratory calibration. Using the data acquired to date, we demonstrate that combining the two measurements allows a more accurate estimate of the cable load, to better than 50 kN.

Many bridges worldwide are approaching the end of their lifespan and it is necessary to assess their health condition in order to mitigate risks, prevent disasters, and plan maintenance activities in an optimized manner. Fracture critical bridges are of particular interest since they have only little or no load path redundancy. Structural health monitoring (SHM) has recently emerged as a branch of engineering, which aim is to improve the assessment of structural condition. Distributed optical fiber sensing technology has opened new possibilities in SHM. A distributed deformation sensor (sensing cable) is sensitive at each point of its length to strain changes and cracks. Such a sensor practically monitors a one-dimensional strain field and can be installed over all the length of the monitored structural members, thereby providing with integrity monitoring, i.e. direct detection and characterization (including recognition, localization, and quantification or rating) of local strain changes generated by damage. Integrity monitoring principles are developed and presented in this article. A large scale laboratory test and a real on-site application are briefly presented.

The dynamic monitoring of civil structures such as buildings and bridges is traditionally approached using acceleration and velocity sensors. When a monitoring program is designed to address concerns related to the level of strain in certain members, fatigue or displacements due to extreme loads, it is sometimes advantageous to measure those parameters directly, instead of deriving them from acceleration or velocity data. Inhomogeneous construction materials such as concrete, stone or masonry require the use of long-gauge sensors to measure strain, since local sensors can provide erroneous data due to local material changes. On the other hand, acceleration and tilt sensors are very useful to capture the global deformations and displacements. The development of long-gauge-length fiber optic sensors can be considered as a useful addition to the toolkit of those interested in the structural dynamics. The system can monitor structures over long periods of time at acquisition frequencies up to 10 kHz and with sub-microstrain resolution. The possibility of obtaining static and dynamic measurements from the same sensor is another advantage of this technology. For acceleration and tilt monitoring, MEMS sensors are now recognized as a powerful and low-cost alternative to more traditional sensor types. Fully-integrated sensors with 3-axis accelerometers and two-axis tiltmeters are now available in a compact packaging that also contain all data acquisition electronics and can be easily deployed in new or existing structures, connecting them directly to an Ethernet network. This contribution briefly introduces fiber optic and MEMS sensing technologies and will than illustrate their application to structural health monitoring through several examples, including the new I35W bridge in Minneapolis USA, the Ile d’Orléans suspension Bridge in Québec Canada and the shaking-table test of a full-scale masonry building reinforced with composite materials.

Structural health monitoring is a process meant to provide accurate and real-time information concerning structural condition and performance. Needs for structural health monitoring in the past two decades increased rapidly, and these needs stimulated the development of various sensing technologies. Distributed optical-fiber sensing technology has opened new possibilities in structural monitoring. A distributed deformation sensor (sensing cable) is sensitive at each point of its length to strain changes and cracks. Such a sensor practically monitors a one-dimensional strain field and can be installed over the entire length of the monitored structural members (suspension cables, bridge girders, tunnel vaults, dam basis, etc.). Therefore, the sensor provides for integrity monitoring, that is, direct detection, characterization (including recognition, localization, and quantification or rating), and report of local strain changes generated by damage. An integrity monitoring principle for long bridges and tunnels is developed. Various distributed sensing techniques are summarized, and their potential for the use in integrity monitoring is compared. Finally, the first large-scale, actual on-site application is briefly presented.

Submillimeter crack is detected with a dedicated fiber-optic strain cable, a 1-m-spatial-resolution (w) distributed Brillouin sensor and an advanced signal processing technique. The signal processing approach consists in spectrum shape analysis and multiple peaks detection.

This paper presents the laboratory validation of a prototype optic-fiber instrumented structural element. The element is a reduced-scale reinforced concrete beam, of dimensions 3.8×0.3×0.5m that can be pre-stressed by an internal Dywidag bar. The sensing technology is based on a multiplexed version of the SOFO strain sensor, prepared in the form of a 3-field smart composite bar; in-line multiplexing is obtained by separating each measurement field through broadband FBGs. The experiment aims to identify the response of the sensors to differing damage conditions artificially produced in the element, including cracking and loss of prestressing. A numerical algo-rithm, based on Bayesian logic, is applied to real-time diagnosis: by processing the sensor meas-urements and prior information, the method assigns a posterior probability to each assumed damage scenario, as well as the updated probability distributions for each relevant structural parameter. With respect to classical damage detection approaches, the merit of those based on Bayesian logic is to provide not only information on the damage, but also the degree of confidence in this informa-tion. The paper discusses the ability of the system to identify the differing damage conditions. The reported test clearly shows that an occurrence such as a loss of prestressing can be recognized early with a high degree of reliability based on the strain data acquired.

From an economic and ecological point of view, reinforced concrete-structure corrosion is a worldwide concern. Although currently, there are several systems for detection corrosion in concrete, no application allows early, precise and nondestructive detection of the presence of chlorides. This article describes the development of a new chemical optical-fiber sensor that measures chloride free concentrations in concrete pores in a quantitative and nondestructive manner. It is based on the principle of fluorescence quenching using a sensitive chloride indicator. This sensor demonstrates good reversible behavior for the detection of free chlorides (between 30mm and 350mM) in the interstitial pores of concrete and therefore it represents a promising type of probe for early and in situ measurements of chlorides in concrete structures.

In this paper, we present the development and laboratory validation of in-line multiplexing for a low-coherence interferometric strain sensor suitable for industrial deployment and application to civil structures. The sensor is the multiplexed version of the standard SOFO, developed, produced and commercialized by Smartec SA. While the standard SOFO employs total reflectors at the end of the measurement and reference fibers, allowing measurement of the strain only over a single field, in the solution presented in-line multiplexing is obtained separating each measurement field by partial reflectors, consisting of broadband Fiber Bragg Gratings (FBGs) with a 5% reflectivity. Laboratory tests have been carried out on a prototype 3-field sensor, to investigate effectiveness, resolution and temperature sensitivity. Outcomes show a linear response of the sensor with RMS resolution lower than 3 µm, independent of the measurement base, of the same order as the single field sensor. Consistently with the theoretical prediction, the system exhibits an apparent thermal expansion coefficient of 2 µe ◦ C −1 , relatively low if compared with the thermal expansion coefficient of steel or concrete structures. This temperature dependency can even be eliminated by appropriate selection of the length of the reference fiber. Theoretical analysis indicates that the maximum number of fields that can be arranged in series is in the order of 10; however this limit can be overcome by appropriately selecting the power of the light source of the interrogation unit. © 2008 Published by Elsevier Inc.

Distributed Optical Fiber Sensing is a mature technology given its strong record of over 20 years. Nevertheless, underground utilities are yet to embrace it as an everyday tool despite its enormous capability. One dimensional long buried utilities and tunnels offer the best application for the use of this technology. Research studies around the world offer the promise of this technology in monitoring the impact of ground movements on underground utilities and tunnels. No application standards existed that governed the use of this technology within any jurisdiction in the world in September 2012. A global task group on optical fiber sensing systems (OFSS) was born to become a unique pool of talent and experience on the subject with over 40 leading experts from 17 countries, which went on to author two companion standards American Society for Testing and Materials (ASTM) F3079-14 and F3092-14, within ASTM Technical Committee F36. This paper provides a brief overview of how OFSS work, what is in these standards, why OFSS is poised to become the most versatile innovation among all measurement tools for field monitoring, what problems the task group faced during the development of the standards and how the members of the task group resolved these problems, what the benefits are of such global standards and the future plans for the global OFSS task group. The most paramount goal of the authors is to share the lessons they learned during the development of the standards with the delegates of this conference.

The paper describes the characteristics of a monitoring system installed on a ca- ble-stayed bridge recently constructed in the Port of Venice. The system is based on the use of the SOFO™ fiber optic sensor family and it has been conceived for both static long-term and periodic dynamic monitoring. The monitoring system has been installed during construction, in order to acquire control over the most significant construction phases, and for permanent static monitoring. Linear deformation sensors and their locations have however been selected in order to allow the execution of periodic dynamic measurements and identification of the structural characteristics. The first analyses of the data collected during the final stages of the construction and just after construction completion are presented. The characteristics of the algorithms that have been selected to interpret the monitoring data are also discussed. The Port Authority of Venice, in the framework of the development of the container and multi- purpose terminals of the Marghera basin, situated at the inner edge of the Venice Lagoon, have decided the construction of a new road link between the national highway system and the port areas. The road link is crossing the "West Industrial Channel" and the railways serving the ter- minals, thus requiring the construction of a long-span bridge. An international competition has been launched for the design of the bridge and related ac- cess viaducts. The preferred design was including a cable-stayed bridge formed by a composite steel and reinforced concrete beam, continuous over two spans of 105 m and 126 m in length, respectively. The bridge axis is a circular segment of 175 m radius. The deck on each of the two spans is supported by 9 cables, composed by 31 to 85 strands, attached to a reinforced concrete

Optical fiber sensor (OFS) technologies have developed rapidly over the last few decades, and various types of OFS have found practical applications in the field of civil engineering. In this paper, which is resulting from the work of the RILEM technical committee “Optical fiber sensors for civil engineering applications”, different kinds of sensing techniques, including change of light intensity, interferometry, fiber Bragg grating, adsorption measurement and distributed sensing, are briefly reviewed to introduce the basic sensing principles. Then, the applications of OFS in highway structures, building structures, geotechnical structures, pipelines as well as cables monitoring are described, with focus on sensor design, installation technique and sensor performance. It is believed that the State-of-the-Art review is helpful to engineers considering the use of OFS in their projects, and can facilitate the wider application of OFS technologies in construction industry.

A full-scale on-site test represents an ideal way to check a hypothesis and to determine the real behavior of structures, especially in cases in which some uncertainties cannot be reduced otherwise. To perform the test successfully it is necessary to monitor the parameters that representatively describe the structural behavior. In the case of piles, axial compression, pullout, and flexure tests cover all load combinations that may appear in service. To assess the foundation performance at a semiconductor production facility, two sets of piles with three piles in each set were tested. The monitored parameters were average strains, registered in several segments over the whole length of each pile using long-gauge fiber optic sensors. This type of sensor, combined in appropriate topologies, gives rich information concerning the piles’ behavior and soil properties. The monitoring method is presented and its performances through the results of the tests are discussed. This method allowed the determination of the Young modulus of the piles, the occurrence of cracks, the normal force distribution, and the ultimate load capacity in the case of axial compression and pullout tests, as well as the curvature distribution, horizontal displacement, deformed shape, and damage localization in the case of the flexure tests. Moreover, the pile–soil friction distributions, the quality of soil, and the pile tip force were estimated. The advantage of the presented method resides in the use of long-gauge sensors, which are insensitive to local structural defects like crack openings or air pockets and allow the collection of data on a global structural level and not on a local material level.

Distributed Fiber optic sensing system is a unique tool for the evaluation of distributed temperature over several kilometers. It is a powerful diagnostic instrument for the identification and localization of potential problems, such as leakages in pipelines and dykes, hot-spots in high-voltage cables and other events that create temperature anomalies. Such distributed temperature sensing (DTS) systems have the advantage of being relatively easy to deploy over long pipeline sections and have been shown to detect leakages events with good accuracy and reliability. However, when distributed fiber optic sensing systems are deployed in security-critical applications, where availability and reliability are crucial, it is important to continuously verify and assess the correct functioning and reliability of the whole system, including the sensing cables, the measurement system, the data analysis software and the alert transmission. In the past, such testing have been performed periodically by the pipeline personnel, but testing frequencies are typically low, e.g. once per year. The DTS Automated Trip Testing System is a fully independent device that is able to produce a controlled and localized thermal anomaly (hot spot or cold spot) and verify its correct detection. This allows a continuous verification of the DTS system reliability and functionality and a periodic statistical evaluation of the confidence level (proven by experience SIL rating). This paper will present more specifically the development, the functioning and deployment, and its applications of an automated system and method for testing the efficacy and reliability of distributed temperature sensing (DTS) systems, in particular those DTS systems used for pipeline leakage detection.

Over the past decades, several major industrial accidents led the chemical industries handling large quantities of dangerous substances and national regulation bodies to reinforce the safety and prevention measures of their installations, in compliance with local laws such as the Seveso II directive in Europe. Indeed, leakages of chemicals can be at the origin of toxic releases, which can have severe consequences on the installations as well as on the environment and nearby inhabitants. Industries are prompted to take all possible measures to reduce the occurrence of such catastrophic events by implementing additional technical safety barriers in order to prevent or mitigate any potential danger on their key structures such as pipelines, reactors, storages, transfer lines, etc. Pipeline leakages may have different origins, such as corrosion, fatigue, material flaws, shocks, abnormal temperatures, extreme pressures, or excessive deformations caused by ground movement. In the case of liquefied or pressurized gases, leakages can be detected by the rapid drop of temperature due to the evaporation of the released liquid and its evaporation gases or due to gas expansion. These local thermal anomalies can be reliably detected by a fiber-optic distributed temperature sensing system able to detect temperature changes of the order of 1°C, with 1m spatial resolution and 10s response time. A fiber optic cable is installed all along the whole length of the pipeline and is connected to a measurement system that can automatically detect temperature anomalies which are telltale of leakages and generate an alert to initiate appropriate response actions on the affected pipeline section. Such a system has been permanently deployed at several industrial and chemicals sites were functional and operational tests have also been carried out. This paper will present the system architecture and installation at an ammonia production, storage, shipping and processing site. Results of simulated leakage detection tests on ammonia pipeline and long-term operation in normal conditions will also be presented.

This paper illustrates an application of Bayesian logic to monitoring data analysis and structural condition state inference. The case study is a 260 m long cable-stayed bridge spanning the Adige River 10 km north of the town of Trento, Italy. This is a statically indeterminate structure, having a composite steel-concrete deck, supported by 12 stay cables. Structural redundancy, possible relaxation losses and an as-built condition differing from design, suggest that long-term load redistribution between cables can be expected. To monitor load redistribution, the owner decided to install a monitoring system which combines built-on-site elasto-magnetic and fiber-optic sensors. In this note, we discuss a rational way to improve the accuracy of the load estimate from the EM sensors taking advantage of the FOS information. More specifically, we use a multi-sensor Bayesian data fusion approach which combines the information from the two sensing systems with the prior knowledge, including design information and the outcomes of laboratory calibration. Using the data acquired to date, we demonstrate that combining the two measurements allows a more accurate estimate of the cable load, to better than 50 kN.

One of the main challenges of the Large Hadron Collider (LHC), a new particle accelerator currently under construction at CERN (the European Organization for Nuclear Research) in Geneva, resides in the design and production of the superconducting dipoles used to steer the particles around a 27 km underground tunnel. These so-called cryodipoles consist of an evacuated cryostat and a cold mass containing the particle tubes and the superconducting dipole magnet. The latter is cooled by superfluid helium at 1.9 K. The particle beams must be centred in the dipole magnetic field with a sub-millimetre accuracy. This requires that the relative displacements between the cryostat and the cold mass must be monitored with great accuracy. Because of the extreme environmental conditions (the displacement measurements must be made in vacuum and between two points at a temperature difference of about 300 degrees) no adequate existing monitoring system was found for this application. It was therefore decided to develop an optical sensor based on low-coherence double interferometry, which measures with micrometer precision the distance between a mirror welded to the dipole cold mass and an optical head attached in the inner wall of the cryostat. This contribution describes the development of this novel sensor and the first measurements performed on the LHC cryodipoles.

The possibilities of the radio-frequency amplitude modulation of a low-coherence source for distance and displacement measurements are discussed. This intensity-based method, used within a Michelson interferometer, is a novel alternative to perform dynamic deformation measurements. The theoretical background is presented, together with the experimental verification of the principle. Besides, the results of the first quasi-dynamic tests are shown and the perspectives of the technique discussed. This method is specially useful for the dynamic monitoring of civil structures, where large measurements bases are needed. Furthermore, the application of the amplitude modulation for distance measurements is demonstrated experimentally.

In many bridges, the vertical displacements are the most relevant parameters to be monitored in both the short and long term. Current methods (such as triangulation, water levels or mechanical extensometers...) are often tedious to use and require the intervention of specialized operators. The resulting complexity and costs limit the temporal frequency of these traditional measurements. The spatial resolution obtained is in general low and only the presence of anomalies in the global structural behavior can be detected and warrant a deeper and more precise evaluation. To measure bridge vertical displacements at low cost and frequently in time, one solution consists of installing a network of fiber optic sensors during concrete pouring or installing them on the surface of the structure. By subdividing the whole structure into structural elements and those elements into cells that are analyzed by the sensors, it is possible to obtain information about the average cell deformation (e.g., mean curvature) that can then be combined to obtain the global structural displacement field. In 1996, a concrete highway bridge near Geneva (Switzerland) was instrumented with more than 100 low-coherence fiber optic deformation sensors. The Versoix Bridge is a classical concrete bridge consisting in two parallel pre-stressed concrete beams supporting a 30-cm concrete deck and two overhangs. To enlarge the bridge, the beams were widened and the overhang extended. In order to increase the knowledge on the interaction between the old and the new concrete, we choose low-coherence fiber optic sensors to measure the displacements of the fresh concrete during the setting phase and to monitor the long term deformations of the bridge. The aim is to retrieve the spatial displacements of the bridge in an earth-bound coordinate system by monitoring its internal deformations. The vertical and horizontal curvatures of the bridge are measured locally at multiple locations along the bridge span by installing sensors at different positions in the girder cross-section. By taking the double integral of the curvature and respecting the boundary conditions, it is then possible to retrieve the deformations of the bridge. This measurement methodology was also applied to the Lutrive Highway Bridge in Switzerland in order to measure the variation in vertical bridge displacements due to a static load test. The results obtained using the low coherence interferometric sensors of the SOFO system were then compared with the displacements obtained through an optic leveling system. In the case of this cantilever bridge of 60 meters half-span equipped with 30 fiber optic sensors, a discrepancy of less than 7% was obtained between the two measuring systems.

All structures undergo deformations under the effects of loads or degradation of the constituent materials. The deformations of any structure (bridges, dams, frames, shells, tunnels, towers, wings, trusses,) contain a lot of information about its health state. By measuring these deformations it is possible to analyse the loading and aging behavior of the structure. The presented method analyses a structure by subdividing it into sections and cells. The deformation of each of these macro-elements is first analysed separately to obtain local information about the materials, and then combined to provide insight on the global behavior. Examples of these techniques applied to civil engineering structures fitted with long-gage-length fiber optic sensors show the variety of information that can be obtained using this powerful analysis technique.

In this paper we discuss an Adaptive Optics (AO) system for the control of geometrical fluctuations in a laser beam based on the interferometric detection of phase front. By comparison with the usual Shack-Hartmann based AO system, we show that this technique is of particular interest when high sensitivity and high band-pass are required for correction of small perturbations like, for instance, the control of the input beam of gravitational waves interferometric detectors. The good results obtained allow us to decide for its application within the mode cleaner system of the 3m prototype optical interferometer on gravitational wave detection (IDGW-3P) developed for R&D and operational in Napoli.

This contribution illustrates an application of Bayesian logic to monitoring data analysis and structural condition state inference. The case study is a cable-stayed bridge 260 m long spanning the Adige River ten kilometers north of the town of Trento, Italy. It is a statically indeterminate structure, consisting of a steel-concrete composite deck, supported by 12 stay cables. Structural redundancy, possible relaxation losses and an as-built condition differing from design, suggest that longterm load redistribution between cables can be expected. To monitor load redistribution, the owner decided to install a monitoring system that combines built-on-site elasto-magnetic and fiber-optic sensors. In this article, we discuss a rational way to improve the accuracy of the load variation, estimated using the elasto-magnetic sensors, taking advantage of the fiber-optic sensors information. More specifically, we use a multi-sensor Bayesian data fusion approach, which combines the information from the two sensing systems with the prior knowledge including design information and outcomes of laboratory calibration. Using the data acquired to date, we demonstrate that combining the two measurements allows a more accurate estimate of the cable load, to better than 50 kN.

This paper illustrates an application of Bayesian logic to monitoring data analysis and structural condition state inference. The case study is a 260 m long cable-stayed bridge spanning the Adige River 10 km north of the town of Trento, Italy. This is a statically indeterminate structure, having a composite steel-concrete deck, supported by 12 stay cables. Structural redundancy, possible relaxation losses and an as-built condition differing from design, suggest that long-term load redistribution between cables can be expected. To monitor load redistribution, the owner decided to install a monitoring system which combines built-on-site elasto-magnetic and fiber-optic sensors. In this note, we discuss a rational way to improve the accuracy of the load estimate from the EM sensors taking advantage of the FOS information. More specifically, we use a multi-sensor Bayesian data fusion approach which combines the information from the two sensing systems with the prior knowledge, including design information and the outcomes of laboratory calibration. Using the data acquired to date, we demonstrate that combining the two measurements allows a more accurate estimate of the cable load, to better than 50 kN.

An important challenge for widespread application of structural health monitoring (SHM) in civil engineering is the creation and implementation of algorithms for automatic and reliable detection of unusual structural behavior. Branko, the lead role and the second author of this paper has been in charge of data analysis of a 19storey tall building. Observation of the data from the instrumentation has over the years, convinced Branko that there is an ongoing differential settlement of one of the base columns, in apparent contrast with his initial expectations. This conclusion matured gradually not only as a consequence of the monitoring results, but also based on verbal information received from a design engineer. Thus, besides the quantitative data provided by the monitoring system, including in the data analysis algorithms the engineer’s knowledge and experience has also been of value. In this study we propose an approach based on Bayesian logic as an effective tool to allow such a blend of field knowledge and SHM results. We show how the whole cognitive process followed by Branko can be suitably reproduced using Bayesian logic. In particular, we discuss to what extent the prior knowledge and potential evidence from inspection, can alter a perception of building behavior based on SHM data alone.

This paper reports on experimental and theoretical investigations into the use of optical fiber sensors in the monitoring of civil engineering structures. For this purpose a highly accurate optical fiber deformation sensor based on low coherence interferometry has been developed. This system was conceived in order to monitor a test concrete slab over a period of years. It enabled the measurement of both concrete shrinkage and elastic coefficient in the whole slab with good reproducibility, in agreement with measurements performed on small concrete samples and with theoretical calculations. The thermal effects on the concrete structures are also presented.

The evaluation of the structural performance of marine structures, such as ship hulls, off-shore platforms and risers requires the monitoring of the static and dynamic strain levels undergone during the whole lifetime. In these environments, the use of passive fiber optic sensors presents advantages in terms of reliability and multiplexing ability. Frequently used structural materials, such as steel and composites, exhibit local defects or discontinuities, such as welds, thickness / diameter variations, marine growths and cracks, introducing discontinuities in the mechanical properties of the material at a local level. Yet, the properties of the material at a global level are more indicative for structural behavior. Therefore, for structural monitoring purposes, it is necessary to use sensors that are insensitive to local material discontinuities. A long-gauge strain or deformation sensor, by definition, is a sensor with a gauge-length several times larger than the maximal distance between discontinuities or the maximal diameter of defects in the monitored material. In this paper we will present the design, testing and applications of a long-gauge fiber optics strain sensor for underwater applications.

Civil structures are important for any society and it is necessary to monitor their health condition in order to mitigate risks, prevent disasters, and plan maintenance activities in an optimized manner. Structural health monitoring (SHM) recently emerged as a branch of engineering with a great potential for addressing the above mentioned challenges. In spite of its importance and promising benefits, SHM is still relatively infrequently used in real structures. A possible reason for this is a lack of understanding of the SHM process, which is often considered to be a supplemental activity that does not require detailed planning. However, the opposite is true - only proper and detailed development and implementation of each SHM step can ensure its successful and maximal performance. The aim of this paper is to present the SHM process through more than 350 projects. Basic concepts are introduced, and the purpose, requirements and benefits of SHM are discussed. The importance of monitoring over a life span is highlighted. Core activities such as creating monitoring strategy, installation and maintenance of hardware, and data management are presented and discussed. The involved parties are identified and their interaction with the monitoring process is analyzed. Finally, important SHM challenges are identified.