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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.

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.

Civil engineering structures are difficult to model accurately and this challenge is compounded when structures are built in uncertain environments. As consequence, their real behavior is hard to predict; such difficulties have important effects on the reliability of damage detection. Such situations encourage the enhancement of traditional approximate structural assessments through in-service measurements and interpretation of monitoring data. While some proposals have recently been made, in general, no current methodology for detection of anomalous behavior from measurement data can be reliably applied to complex structures in practical situations. This paper presents two new methodologies for model-free data interpretation to identify and localize anomalous behavior in civil engineering structures. Two statistical methods (i) moving principal component analysis and (ii) moving correlation analysis have been demonstrated to be useful for damage detection during continuous static monitoring of civil structures. The algorithms are designed to learn characteristics of time series generated by sensor data during a period called the initialization phase where the structure is assumed to behave normally. This phase subsequently helps identify those behaviors which can be classified as anomalous. In this way the new methodologies can effectively identify anomalous behaviors without explicit (and costly) knowledge of structural characteristics such as geometry and models of behavior. The methodologies have been tested on numerically simulated elements with sensors at a range of damage severities. A comparative study with wavelet and other statistical analyses demonstrates superior performance for identifying the presence of damage.

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.

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.

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.

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.

Sub-millimeter crack is detected with a dedicated fiber optic strain cable, a 1 m spatial resolution (w) distributed Brillouin sensor (DBS) and an advanced signal processing technique.

Curved concrete bridge girders have very complex internal forces, stress and strain distribution. As a consequence of their shape, not only the usual bending moments and shear forces are generated, but also important torsion moments are created. These moments "rotate" the axes of principal tensional stresses increasing the risk of cracking. Post-tensioning can prevent the cracks, but the added compression forces introduced in different directions increase the complexity of stress and strain fields. Therefore, the curved post-tensioned concrete girders must be particularly designed and carefully constructed. However, the real structural behavior should be verified, and risks and uncertainties related to structural design and quality of construction minimized. Structural health monitoring is a natural solution for these issues. Structural health monitoring method, based on the use of fiber optic interferometric technology including long-gage sensors and inclinometers, is presented in this paper. A 36 meters long curved post-tensioned bridge box girder is equipped with so-called parallel and so-called crossed sensor topologies, and inclinometers, in order to monitor axial strain, both horizontal and vertical curvature changes, torsion, average shear strain and rotations in both vertical plans. Important parts of structure life such as construction, post-tensioning and first years of service are registered, analyzed and presented.

This paper introduces a concept of smart structural elements for the real-time condition monitoring of bridges. These are prefabricated reinforced concrete elements embedding a permanent sensing system and capable of self-diagnosis when in operation. The real-time assessment is automatically controlled by a numerical algorithm founded on Bayesian logic: the method assigns a probability to each possible damage scenario, and estimates the statistical distribution of the damage parameters involved (such as location and extent). To verify the effectiveness of the technology, we produced and tested in the laboratory a reduced-scale smart beam prototype. The specimen is 3.8 m long and has cross-section 0.3 by 0.5m, and has been prestressed using a Dywidag bar, in such a way as to control the preload level. The sensor system includes a multiplexed version of SOFO interferometric sensors mounted on a composite bar, along with a number of traditional metal-foil strain gauges. The method allowed clear recognition of increasing fault states, simulated on the beam by gradually reducing the prestress level.

One of the advantages of fiber optics with respect to traditional electrical gauges is they can act both as sensors and as a pathway for signals produced by other sensors. This feature allows adoption of a simple sensor system architecture, even when arrays of many sensors are needed. In this paper, we present the development and laboratory validation of in-line multiplexing for the low-coherence interferometric SOFO standard deformation sensor. A standard SOFO, as developed, produced and commercialized by Smartec SA, employs total reflectors at the end of the measurement and the reference fibers, allowing measurement of the strain over a single field. In the solution presented, broadband Fiber Bragg Gratings (FBGs) are employed as partial reflectors to obtain in-line multiplexing. These FBGs, presenting a 5% reflectivity in their reflection spectra, are produced using a chirped phase mask. An experiment was carried out on a 3-field sensor, to investigate effectiveness, resolution and temperature sensitivity. Outcomes show clear fringe visibility for each pair of gratings and a resolution of about 2.5 mm RMS, of the same order as the single field sensor. Issues regarding the maximum number of measurement fields on a single line and deformation range limits are discussed.

Gotaalvbron, the bridge over Gota river, was built in thirties and is now more than seventy years old. The steel girders were cracked and two issues are in cause of steel cracking: fatigue and mediocre quality of the steel. The bridge authorities repaired the bridge and decided to keep it in service for the next fifteen years, but in order to increase the safety and reduce uncertainties related to the bridge performance an integrity monitoring system has been mandatory. The main issue related to selection of the monitoring system has been the total length of the girders which is for all the nine girders more than 9 km. It was therefore decided to monitor the most loaded five girders (total length of 5 km approximately) and logically a fiber optic distributed sensing system have been selected. For the first time a truly distributed fiber optic sensing system, based on Brillouin scattering effect, is employed on such large scale to monitor new crack occurrence and unusual strain development. The monitoring system itself, the monitoring strategy, challenges related to installation and the data management are presented in this paper.

Distributed fiber optic sensing presents unique features that have no match in conventional sensing techniques. The ability to measure temperatures and strain at thousands of points along a single fiber is particularly interesting for the monitoring of large structures such as pipelines, flow lines, oil wells, dams and dikes. Sensing systems based on Brillouin and Raman scattering have been used for example to detect pipeline leakages, verify pipeline operational parameters, prevent failure of pipelines installed in landslide areas, optimize oil production from wells and detect hotspots in high-power cables. The measurement instruments have been vastly improved in terms of spatial, temperature and strain resolution, distance range, measurement time, data processing and system cost. Analyzers for Brillouin and Raman scattering are now commercially available and offer reliable operation in field conditions. New application opportunities have however demonstrated that the design and production of sensing cables is a critical element for the success of any distributed sensing instrumentation project. Although standard telecommunication cables can be effectively used for sensing ordinary temperatures, monitoring high and low temperatures or distributed strain present unique challenges that require specific cable designs. This contribution presents three cable designs for high-temperature sensing, strain sensing and combined strain and temperature monitoring as well as the respective testing procedures during production and in the field.

Distributed fiber optic sensing presents unique features that have no match in conventional sensing techniques. The ability to measure temperatures and strain at thousands of points along a single fiber is particularly interesting for the monitoring of elongated structures such as pipelines, flow lines, oil wells, and coiled tubing. Sensing systems based on Brillouin and Raman scattering are used, for example, to detect pipeline leakages, to verify pipeline operational parameters and to prevent failure of pipelines installed in landslide areas, to optimize oil production from wells, and to detect hot spots in high-power cables. Recent developments in distributed fiber sensing technology allow the monitoring of 60 km of pipeline from a single instrument and of up to 300 km with the use of optical amplifiers. New application opportunities have demonstrated that the design and production of sensing cables are a critical element for the success of any distributed sensing instrumentation project. Although some telecommunication cables can be effectively used for sensing ordinary temperatures, monitoring high and low temperatures or distributed strain presents unique challenges that require specific cable designs. This contribution presents advances in long-range distributed sensing and in novel sensing cable designs for distributed temperature and strain sensing. This paper also reports a number of significant field application examples of this technology, including leakage detection on brine and gas pipelines, strain monitoring on gas pipelines and combined strain and temperature monitoring on composite flow lines, and composite coiled tubing pipes.

Distributed fiber optic sensing presents unique features that have no match in conventional sensing techniques. The ability to measure temperatures and strain at thousands of points along a single fiber is particularly interesting for the monitoring of large structures such as pipelines, flow lines, oil wells, dams and dikes. Sensing systems based on Brillouin and Raman scattering have been used for example to detect pipeline leakages, verify pipeline operational parameters, prevent failure of pipelines installed in landslide areas, optimize oil production from wells and detect hotspots in high-power cables. The measurement instruments have been vastly improved in terms of spatial, temperature and strain resolution, distance range, measurement time, data processing and system cost. Analyzers for Brillouin and Raman scattering are now commercially available and offer reliable operation in field conditions. New application opportunities have however demonstrated that the design and production of sensing cables is a critical element for the success of any distributed sensing instrumentation project. Although standard telecommunication cables can be effectively used for sensing ordinary temperatures, monitoring high and low temperatures or distributed strain present unique challenges that require specific cable designs. This contribution presents three cable designs for high-temperature sensing, strain sensing and combined strain and temperature monitoring.

With increased interest in the use of compressed gas as a vehicle fuel, attention has been focussed on the safety issues surrounding the tanks used to store the fuel. Currently it is necessary to remove the tanks from the vehicle in order to inspect them, which entails a considerable cost in manpower and takes the vehicle being out of service. We have been developing a sensor scheme that can provide in situ monitoring of the tanks condition. This entails bonding optical fibre sensors to the tank and using them to measure the strains experienced by the tank during pressurisation. If the tank is significantly damaged, then the tank will expand in a distorted manner. We therefore measure the strain characteristics of a healthy tank and use them as a reference for future measurements. The method of strain measurement is the well established rf subcarrier phase detection technique, however in this application the changes in optical power caused by microbending of the fibres during pressurisation produces inaccuracies. In order to overcome this problem we use both in- phase and quadrature mixing and then take the ratio of the outputs to obtain a value of arctangent that is independent of amplitude.

Establishing and testing the performance of a monitoring system designed for long-term applications presents some challenges that do not always apply to other measurement instruments. The evolution of the main measurement parameters must be evaluated over long periods of time and the reliability and failure rate must be estimated in a statistically sound procedure. When establishing testing procedures for any system it is important to achieve three goal: the procedures must be based on traceable international standards, the procedures must be reproducible by the system users or third-parties testing authorities and the procedure should be applicable to different measurement systems to allow a fair comparison of the respective performances. This contribution describes the main testing procedures used to test the compliance of SMARTEC's SOFO system components to the published specifications. It also offers a general overview of some issues related to the testing of long-term performances.

®sensors have been in use for the last 10 years for the monitoring of civil, geotechnical, oil & Fiber optic sensing systems are increasingly recognized as a very attractive choice for structural health monitoring. Moving form demonstration project to industrial applications requires an integrated approach where the most appropriate technologies are combined to meet the user’s requirements. In this context it is often necessary and desirable to combine different sensing technologies in the same project. A bridgemonitoring project might for example require long-gauge interferometric sensors to monitor the concrete deck, interferometric inclinometers for the piles and fiber Bragg grating sensors for the monitoring of the strains in the steel beams and for measuring temperatures. Although fiber optic sensors relying on different technologies can easily be combined at the packaging and cable levels, they often require dedicated instruments to be demodulated. A unified demodulation system would therefore be very attractive. This paper describes a technique relying on the analysis of reflected spectra and allowing the demodulation of interferometric (Michelson or Faby-Perot) sensors and fiber Bragg grating sensors with a single measurement system. It also compares the obtained performance in terms of resolution and dynamic range with the available dedicated systems.

Two goals are pursued in this paper. The first goal consists of comparing the performance of the innovative SOFO dynamic system, which uses long-gauge fiber-optic sensors, with the traditional monitoring method based on accelerometers. For this purpose, a dynamic laboratory test was carried out, and measurements were taken from a single-storey threedimensional steel frame model excited at the base by a shaking table. The SOFO dynamic system was installed on one column of the frame structure, while two accelerometers were mounted on the base and on the frame storey, respectively, for comparison. The use of fiber-optic sensors allows to overcome the difficulties associated with the traditional dynamic measurement methods, such as the limitations in the number and in the locations of the monitoring devices. Furthermore, the long-gauge fiber-optic strain sensors show a very high sensitivity and extend the frequency range (1mHz-1KHz). The second goal is to investigate the sensitivity to local damage of a recently proposed method for damage detection and localization. Indeed, the use of better performing long-gauge strain sensors allows the detection of local damage that is hardly visible in the global response of the structure. Damages of increasing intensities are therefore gradually introduced in the structure, and the measurements acquisition is repeated for each of the damaged cases. The SHM-RSM method, which is based on the idea of using a response surface model to approximate the relationship between the measurements collected by different sensors during the same test, is finally applied to the collected data to detect and locate the damages of different intensities.

Owners must manage and ensure the safety of their civil structures even as use of many structures extends well beyond their design lifetime. Traditionally, most structures rely on strict maintenance procedures, visual inspections, and very few sensors. But maintenance is very expensive, visual inspections can miss critical problems, and conventional sensors can fail in harsh environments. Can fiber-optic sensing (FOS) address these issues? This is not a new question, but there are some new answers. This paper highlights several structures where FOS is used, and describes the associated successes and challenges for each application. Many successes are coupled to improved FOS tools: better sensor packages, simpler and less expensive instrumentation, improved installation techniques, and more efficient data analysis tools. Examples of each are provided. Particular attention is given to the economics of instrumenting civil structures - when and how it pays. Conclusions include recommendations for future developments that will further accelerate FOS acceptance and use.

In order to maintain sustainability of infrastructures in which have significant influence to social lifelines, an economical and rational maintenance management system is absolutely needed. Maintenance management of infrastructures and reduction of their life cycle cost (LCC), become serious problems those have to be solved urgently. In this paper, Structural health monitoring based maintenance (SHMBM) aimed to reduce structure’s life cycle cost is proposed. Theoretical background of SHMBM and contribution of monitoring information in LCC reduction are reviewed. As the tools to retrieve the structural deformational properties information, the intelligent sensory principles and their sensory system are introduced such as GPS based MMS monitoring technology, peak memory sensory technology, elasto-magnetic sensory technology and fiber optical sensory technology. Their reliabilities were verified by some verification test and field application test. Some examples of SHMBM application in the monitoring of structural properties are also described as well.

The Compressed Natural Gas (CNG) used as a carburant in automotive industry offers low cost and notably less pollution. Full composite tank used to store the CNG onboard features low weight and extended lifespan. However, the safety issues and maintenance fees remain a challenge for its use in ordinary cars. The structural health monitoring of tanks with accent to damage detection can significantly increase the safety and decrease the maintenance fees. Structural health monitoring and damage detection of composite tanks impose important challenges to the monitoring strategy and monitoring system to be used. The issues of non -intrusive installation of sensors, their topologies and network, and particularly analysis and interpretation of resulting data are very complex. The long-gage interferometric sensors of SOFO type, for direct embedding in the full composite tank during production are developed. The sensor consists of single mode optical fiber embedded into the very thin composite tape. Such packaging offers to optical fiber excellent protection during handling and embedding and makes sensor non-intrusive to the tank material. Appropriate topologies of the sensors are combined in single sensor network used to monitor strain state and damage. The results of monitoring are analyzed at several levels, and the damage is detect ed using algorithms combining the global deformation and changes in both the tank stiffness and sensors cross-correlation. The monitoring strategy, sensors used in full composite tank monitoring, installation issues and the results of the structural health monitoring performed in laboratory are presented in details in this paper.

Establishing and testing the performance of a monitoring system designed for long-term applications presents some challenges that do not always apply to other measurement instruments. The evolution of the main measurement parameters must be evaluated over long periods of time and the reliability and failure-rate must be estimated in a statistically sound procedure. When establishing testing procedures for any system it is important to achieve three goal: the procedures must be based on traceable international standards, the procedures must be reproducible by the system users or third-parties testing authorities and the tests should be applicable to different measurement systems to allow a fair comparison of the respective performances. This contribution describes the main procedures used to test the compliance of SMARTEC's SOFO system components to the published specifications. It also offers a general overview of some issues related to the testing of long-term system performances.

Once every generation, Switzerland treats itself to a National Exhibition commissioned by the Swiss Confederation. Expo 02 was spread out in five "Arteplage" over a whole region: the land of the three lakes, on the shores of the lakes of Biel, Murten and Neuchatel, which are located in the northwest of Switzerland. Each "Arteplage" relates to a theme, which is reflected in its architectures and exhibitions. The "Arteplage" of Neuchatel was related to "Nature and Artificiality;" A big steel-wood whale eating a village represents the fairy tale named "Pinocchio" from the Italian writer Collodi. The "Piazza Pinocchio" was built together with other exposition buildings on one large artificial peninsula. The belly of the whale holds the exposition dedicated to robotic and artificial intelligence, while the rest of the village was developed on two floors with steel piles/beams and wood walls and floors. A fiber optic sensor system was commissioned to monitor the visitor's loads over the whole "Piazza Pinocchio." The main requirements were: real-time computer-screen figure-form results of the live loads during 18 hours a day, automatic thermal-induced strain compensation, real-time warnings and pre-warnings for each single pile, automatic phone call advises when reaching warning thresholds and remote monitoring for complete management of the monitoring sytem. The SOFO system based on low coherence fiber optic deformation sensors was selected to carry out the requirements. The aim of this paper is to present an overview of the project, the installation solution, the results, and data analysis of the installed monitoring system.

The construction and maintenance of the civil infrastructure represents between 10% and 20% of the public investment in most European countries. In the last decade we have however witnessed an increasing shift from investments in the construction of new structures to the maintenance and the lifetime extension of the existing ones. With the exception of the high-speed train lines, most of the transporataion network, including highways and railway, is completed and in service. However, the steady increase of the passengers and goods circulating in the continent, amplified by the free circulation policy introduced by the European Community, is putting the civil infrastructrue under a rude test. Many bridges and tunnels built a few tens of years ago need repair and in many cases an extension of their bearing capacity and lifetime that exceed the original plans. Besides the direct costs associated with these interventions, the disruption to the normal use of the structures causes additional inconveniences including traffic jams and accidents that carry additional hidden costs.

A new central railway station - Lehrter Bahnhof - is being built in Berlin. Because of construction activities in immediate vicinity and because of difficult soil conditions, different vertical displacements have to be expected. In order to avoid damage to the bridges and to a widely spanned glass roof which will be supported by two concrete bridges these two bridges have to be monitored with regard to their deformation performance right from the beginning of construction until commissioning as well as later on for several years. For this purpose, a monitoring concept has been developed and sensors with excellent long-term stability have been chosen. This paper describes the system for monitoring settlements and heaves by means of laser-based optics and hydrostatic leveling. Additionally, strain and inclination of the prestressed concrete bridges are redundantly monitored by embedded long-gage length fiber-optic strain sensors as well as resistive strain gages, and inclinometers. Measurements on-site are referenced by measurements on two test beams well-defined loaded under laboratory and field conditions. The paper also describes the measuring concept and the sensor techniques as well as installation of the sensor system and first results.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The introduction of long-gauge fiber optic sensors has opened new opportunities for the monitoring of large structures. Using these sensors it is possible to observe the local elongation of a structure and calculate its global deformations. The use of internal sensors detecting integrated strain is however unable to detect the rigid-body motion of a structure, relative to an external reference system. This would require the installation of long deformation sensors connecting the structure with external reference points. Another possibility is to use gravity as a reference to measure vertical rotations of the structure. A gravity -referenced rotation sensor is conventionally called an inclinometer and measures the angle variations between a nominally vertical reference line in the structure and the direction of gravity. It is possible to use uni-axial inclinometers or bi -axial ones, measuring rotations in the two perpendicular vertical planes. Today’s inclinometers are based on a variety of techniques and can achieve sensitivities in the micro-radian range. When using fiber optic deformations sensors in a given structure, it would however be interesting to use the same technology to obtain inclination reading [1]. This prompted us to develop a fiber optic-based inclinometer compatible with the SOFO system [2]. This contribution describes the development of this novel sensor and the first measurements obtained with it.

The Siggenthal Bridge is a concrete arch bridge with an arch span of 117 m, being built over the Limmat River in Baden, Switzerland. This bridge has been instrumented with 58 long- gage SOFO fiber optic deformation sensors, 2 inclinometers and 8 temperature sensors to monitor its deformations, curvatures and displacements during construction and int eh long-term. The sensor have been built installed successfully and the arch was monitored during the removal of the formwork and supports. It was therefore possible to observe the deformations of the arch wen being loaded by its dead load and by the daily temperature fluctuations. The measurements have shown that the temperature changes produce deformations of the same order of magnitude as the dead loads. The out-of-plain displacements obtained by double- integration of the measured curvatures are in good agreement with the direct triangulation measurements. Monitoring was also carried out during the construction of the superstructure, with the associated change of the load distribution in the arch. This paper briefly introduces the functional principle of the long-gage sensors used in this application, illustrates their installation and discusses the measurement results obtained during the bridge construction.

This paper resumes the nine year long experience of our group in the installation of fiber optic sensors in the most diverse structure types, including bridges, tunnels, dams, piles, anchors, historical monuments, nuclear power plants and many others. To date, we have installed about 1'500 sensors in almost 70 different applications. Statistics show that, by proper handling, it is possible to achieve 95 - 100% survivability during installation and for many years afterward.

SOFO is a structural monitoring system using fiber optic deformation sensors. It is able to measure deformations between two points in a structure, which can be from 20 cm up to 10 meters (or more) apart with a resolution of two microns (2/1000 mm) even over years of measurements. The system is composed of optical deformation sensors adapted to direct concrete embedding or surface mounting, the cable network, the reading unit and the data acquisition and analysis software. The system is particularly adapted to precise short and long-term deformation monitoring of large structures. An array of more than 60 sensors have been installed on the pier of San Giorgio Levante in the Genoa harbor. These sensors allow the measurement of the pier displacements during the dredging works, ship docking and in the long term. The sensors measure the curvature changes in the horizontal and vertical planes and allow a localization of settlements with a spatial resolution of 10 m over a total length of 400 m. The sensors can be measured automatically and remotely. This paper presents the sensor installation and the results from the first monitoring period..

SOFO is a structural monitoring system using fiber optic deformation sensors. It is able to measure deformations between two points in a structure, which can be from 20 cm up to 10 meters (or more) apart with a resolution of two microns (2/1000 mm) even over years of measurements. The system is composed of optical deformation sensors adapted to direct concrete embedding or surface mounting, the cable network, the reading unit and the data acquisition and analysis software. The system is particularly adapted to precise short and long-term deformation monitoring of large structures. An array of more than 60 sensors have been installed on the pier of San Giorgio Levante in the Genoa harbor. These sensors allow the measurement of the pier displacements during the dredging works, ship docking and in the long term. The sensors measure the curvature changes in the horizontal and vertical planes and allow a localization of settlements with a spatial resolution of 10 m over a total length of 400 m. The sensors can be measured automatically and remotely. This paper presents the sensor installation and the results from the first monitoring period.

The monitoring of geotechnical structures like piles, anchors and tunnels requires the measurement of deformations over bases of a few meters to a few tens of meters. The SOFO monitoring system, based on the use of long-gage low-coherence interferometric sensors therefore presents interesting application opportunities in this domain. The SOFO system was installed in a number of piles to monitor their short an long term deformations, to evaluate the lateral friction and to assess their ultimate bearing capacity. The sensors were also installed inside anchor cables to measure the deformations of the rock, in the free and in the anchored parts. Additional sensors were installed directly on single cable strands. This paper presents the sensor installation and the results from selected applications in the monitoring of piles and anchors.

SOFO is a fiber optic sensor system that allows the monitoring of micrometer deformations over measurement bases up to a few meters. It is particularly adapted to measure civil structures built with conventional civil engineering materials (concrete, steel and timber). It has been successfully tested in different type of structures such as bridges, tunnels and piles. The application of the system is however limited in some case when unusual materials are used in the construction and in other cases by the dimensions of the standard SOFO sensors. To extend the domain of application of the current system, special sensors have been developed. In this paper we present four special SOFO sensors: long, membrane, thin and stiff sensors. The long sensor has a measurement basis of several tenths of meters and its purpose is the measurement of deformations in massive and large structures (dames, tunnels). The membrane sensor is for use on laminated materials (e.g. membrane roofing) and it is easy to install by simply gluing it to the structure to be monitored. Since standard sensors can not be used for thin mortar layers because of their cross-section, a thin sensor has been developed, too. Finally, the aim of the stiff sensor is to determine the hardening (solidification) time of concrete. This time is determined by comparing the deformations of a stiff and a standard sensor, closely placed in the concrete at the very early age. The design of these sensors is presented along with significant application examples.

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 paper presents the sensor network design and the measurements that were performed during the construction phases, during the bridge operation since it was reopened and under a recent static-loading test.

The security of civil engineering works demands a periodical monitoring of the structures. The current methods (such as triangulation, water levels, vibrating strings or mechanical extensometers) are often of tedious application and require the intervention of specialized operators. The resulting complexity and costs limit the frequency of these measurements. The obtained spatial resolution is in general low and only the presence of anomalies in the global behavior urges a deeper and more precise evaluation. There is therefore a real need for a tool allowing an automatic and permanent monitoring from within the structure itself and with high precision and good spatial resolution. In many civil structures like bridges, tunnels and dams, the deformations are the most relevant parameter to be monitored in both short and long-terms. Strain monitoring gives only local information about the material behavior and too many such sensors would therefore be necessary to gain a complete understanding of the structure's behavior. We have found that fiber optic deformation sensors, with measurement bases of the order of one to a few meters, can give useful information both during the construction phases and in the long term. In the case of beams and bridges, long-gate sensors can be used to evaluate the curvature variations and calculate the horizontal and vertical displacements by double integration of the curvatures.