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In this paper, we propose a method that allows to estimate the vertical displacement of a two-dimensional structure by means of strain measurements. Fifteen fiber Bragg gratings (FBGs) 10 mm long have been selected as strain sensors and embedded in a rectangular multilayer panel in order to test the proposed method. Only few optical fibers have been employed avoiding the complex wiring typical of the electrical sensors. The deflection tests have been carried out loading the panel in different configurations. Once the deflection maps were obtained, the values in the center were compared with the displacements directly measured by means of a mechanical comparator finding a very good agreement.

The present work is devoted to analyze the potentiality of satellite-based techniques for structural monitoring of bridges. Specifically, the well-known case study of the cable stayed bridge across the river Garigliano and Ausente stream is presented. The available “in situ” data have been compared and integrated with satellite-based measurements (ERS, ENVISAT satellites) for the common monitoring period (1993-2004); thus, the temporal observation window has been extended until 2010 (ENVISAT satellite). DInSAR represents a consolidated tool for deformation monitoring and its application on man-made structures and infrastructures can make easier the detection of potential problems with a consequent improvement of risks management.

Over the last few years, fiber optic sensors (FOS) have seen an increased acceptance and widespread use in industrial sensing and in structural monitoring in civil, aerospace, marine, oil & gas, composites and other applications. One of the most prevalent types in use today are fiber Bragg grating (FBG) sensors. Historically, FOS have been an attractive solution because of their EM immunity and suitability for use in harsh environments and rugged applications with extreme temperatures, radiation exposure, EM fields, high voltages, water contact, flammable atmospheres, or other hazards. FBG sensors have demonstrated that can operate reliably in many different harsh environment applications but proper type and fabrication process are needed, along with suitable packaging and installation procedure. In this paper, we review the impact that external factors and environmental conditions play on FBG’s performance and reliability, and describe the appropriate sensor types and protection requirements suitable for a variety of harsh environment applications in industrial furnaces, cryogenic coolers, nuclear plants, maritime vessels, oil & gas wells, aerospace crafts, automobiles, and others.

The FBG sensor has globally been commercialized in various fields that is actively applied in Korea as well. Especially it is widely used as a structural monitoring sensor in civil engineering and construction structures due to its advantages including electrical stability, chemical stability and multiplexing. This report aims to introduce safety inspection of the FBG sensor in respect of radioactivity which has been applied to a silo structure for radioactive waste disposal as an example.

Thirty years ago the Air Force initiated Project Forecast II, a Sagnac fiber optic strain sensor had been used to measure strain fields internal to carbon composites provided by Douglas Aircraft and issues associated with monitoring the structural integrity of the McDonnell Douglas Space Station design all came together to initiate the new field of fiber optic smart structures. This tutorial paper is intended to provide a perspective of how the field originated and has evolved of the past 30 years.

This paper provides an overview of selected applications of high speed structural monitoring using fiber grating sensors. Rapid and effective diagnostic capabilities are necessary to respond to changes in structural integrity that may affect safety. In the case of aerospace structures operating at high velocity rapid response has the potential to mitigate catastrophic failure. Similar safety issues apply to civil structures where timely decisions are critical to operations of bridges, dams and buildings. Rapid responses for oil and gas, medical and environmental monitoring applications are also highly important. A great deal of progress has been made in improving the quality and capabilities of high speed fiber grating sensor systems. Some of these systems will be discussed.

New federal regulations now mandate North American railroad bridge owners to cl osely assess the structural capacity of their bridges. Consequently, railroad companies are currently looking into developing and exploring monitoring systems for specific bridges, to help them improve and develop bridge sa fety in order to help comply with this new rule. The first part of this paper explains the significance of the new federal law. The new rule comes from the Federal Railroad Administration (FRA), Department of Transportation (DOT), and it falls under the 49 Code of Federal Regulations (CFR), Parts 213 and 237 1 . It requires railroad track owners to know the sa fe capacity of their bridges and to additionally conduct special inspections if either weather or other exceptional conditions ma ke them necessary to ensure safe railroad bridge operations. The second part of this paper will cover past and current studies about the viability of bridge health monitoring, and actual structural monitoring experiences for railroad bridges. Finally, lessons learned from these monitoring examples, as well as recommendations for future applications, are suggested, including wireless monitoring strategies for railroad bridges such as: campaign sensing inspections (periodic monitoring); bridge replacement observations (short term monitoring); and permanent bridge instrumentation (long term monitoring). Keywords: railroad bridges, structural health monitoring, maintenance, safety, bridge management, bridge decay, dynamic monitoring, displacement monitoring.

Wheel flats are a major source of problems in railway systems since they cause strong wear both in the infrastructure and in the train vehicles. In this paper, we present field tests concerning the application of Fiber Bragg Grating (FBG) sensors for the detection of out-of-roundness in high-speed train wheels. Wheel flats are shown to cause high-energy impacts on the rails that can be monitored using FBGs located in the rails. The results point out a great potential of this technology for the development of reliable wheel flat detection systems. © 2013 IEEE.

This paper describes selected work in the area of fiber optic smart structures performed by the author and his colleagues at McDonnell Douglas, Blue Road Research and Columbia Gorge Research over the past 25 years. It is intended to provide an overview of some of the developments in the field and how it evolved over this time span. Application areas that will be addressed include aerospace, civil structures and composite materials.

In the application of micro-structural monitoring, one kind of flexible and stretchable sensing elements was urgently demanded to detect the micro-bending and surface distortions, such as micro-bend sensing elements of medical catheter or smart skin sensing unit of micro-robots. Here the sensing element must be stretchable and flexible for free operation, and must be safe enough when used in bio-medical situation. Although the optical fiber grating is very mature and can be used as sensing element in micro-bending situation, it isn't stretchable enough and flexible enough when used in bio-medical science and micro- structural monitoring, and when applied in human body, the fiber grating isn't safe enough for its easily broken character. In this paper a kind of novel flexible and stretchable polymer grating sensing elements was fabricated by micro-replication process which could be used in micro- structural monitoring, and detailed processes was presented and discussed.

We present a simple, low-cost, temperature- and strain-insensitive long-period gratings (LPGs) written in photonic crystal fibers (PCFs) that can be used as sensitive chemical solution sensors or bend sensors for a variety of industrial applications, including civil engineering, aircraft, chemistry, food industry, and biosensing. Three different configurations of PCFs have been used for this study, including a polarization maintaining PCF, a large mode area PCF and an endlessly single mode PCF. These LPGs have been characterized for their sensitivity to temperature, strain, bending, and surrounding refractive index. Transmission spectra of the LPGs were found to exhibit negligible temperature and strain sensitivities, whereas possessing usable sensitivity to refractive index and bending. This type of PCF sensor could in principle be designed for optimum sensitivity to desired measurand(s), while minimizing or removing undesirable cross-sensitivities. The unique sensing features of PCFs are particularly suited for a wide variety of applications in smart structures, embedded materials, telecommunications and sensor systems.

A number of efforts had been sought to instrument bridges for the purpose of structural monitoring and assessment. The outcome of these efforts, as gauged by advances in the understanding of the definition of structural damage and their role in sensor selection as well as in the design of cost and data-effective monitoring systems, has itself been difficult to assess. The authors' experience with the design, calibration, and operation of a monitoring system for the Kishwaukee Bridge in Illinois has provided several lessons that bear upon these concerns. The systems have performed well in providing a continuous, low-cost monitoring platform for bridge engineers with immediate relevant information. Experiences learned from the design and installation of health monitoring systems for several major long span bridges in Japan and China will be addressed.

The computational and wireless communication capabilities of smart sensors densely distributed over structures can provide rich information for structural monitoring. While smart sensor technology has seen substantial advances during recent years, interdisciplinary efforts to address issues in sensors, networks, and application specific algorithms are needed to realize their potential. This paper first discusses each of these issues, and then reports on research that combines the results to develop a structural health monitoring (SHM) system suitable for implementation on a network of smart sensors. Experimental verification is provided using Intel's Imote2 smart sensors installed on a threedimensional truss structure. The Imote2 is employed herein because it has the high computational and wireless communication performance required for advanced SHM applications. This SHM system is then investigated from sensing, network, and SHM algorithm perspectives.

FBG sensors are more and more accepted in most area of Structure Health Monitoring. However, due to the fact that FBG senses both strain and temperature is monitored simultaneously, temperature compensation for FBG strain sensors of long-term structural monitoring is indispensable. In this paper, based on the FBG's strain and temperature sensing principles, a novel FBG-based sensor for simultaneous dual-measurement of pressure and temperature has been developed. Firstly, in consideration of the requirement of sensors, a novel sensor structure has been designed and its sensing principle is given in details. Secondly, the properties of FBG-based sensor for simultaneous dual-measurement of pressure have been tested by some experiments. Finally, theoretical sensitivity has been compared with that from experiments. The research results show that the FBG-based sensor for simultaneous dual-measurement of pressure has good linearity, repetition, immunity of temperature changes. Such kind of FBG-based sensor for simultaneous dual-measurement ofpressure can be used to practical monitors.

This paper attempts to validate the effectiveness of wireless sensor unit by field experiments on a self-anchored suspension bridge. This wireless sensor unit was developed at Konyang University's SIS lab in Korea for real-time dynamic response measurement of structures. This sensing unit called SWMAS(Smart Wireless MEMS-based Sensor System) consists of a sensor system module, a control and processing module, and a wireless modem module. In order to evaluate whether SWMAS would be applicable to structural monitoring system, experiments were performed to a full-scaled structure, which was a self-anchored suspension bridge, a wire-based monitoring system placed inside. In the field experiments, the data from the ambient vibrations of the bridge were acquired in real-time using SWMAS. All data acquired were compared with those of wire-based monitoring system. As a result, the comparison proved that SWMAS would be effectively applicable to smart monitoring system.

FBG strain sensors are more and more accepted in the area of structural health monitoring, especially in civil infrastructures. However, due to the fact that FBG senses both strain and temperature simultaneously. And moreover the wavelength shift induced by 1°C is almost equivalent to that induced by 10μe. So temperature compensation for FBG strain sensors of long-term structural monitoring is indispensable. In this paper, based on the FBG's strain and temperature sensing principles, the techniques of dual FBGs temperature compensation and the environmental temperature compensation are brought forward. The experiment of cement paste curing monitroed by dual FBGs was carried out. And the advantage of the technique of dual FBGs temperature compensation are proved, which is proper for long-term structureal monitoring system for civil infrastructures.

There is a growing need for built-in monitoring systems for civil engineering infrastructures, due to problems such as increasing traffic loads and rising costs of maintenance and repair. Fibre optic sensors (FOS), capable of reading various parameters are promising candidates for life-long health monitoring of these structures. However, since FOS have only been introduced recently into the field of structural monitoring, their acceptance and widespread implementation will be conditioned by their durability under severe climatic and loading conditions. This paper reports on the performance of strain extrinsic FOS attached to carbon fibre reinforced polymer (CFRP) plates used to strengthen concrete structures. The specimens tested in this project are reinforced concrete (RC) beams with an additional external CFRP reinforcement. The FOS-instrumented beams were first subjected to fatigue loading for various numbers of cycles and load amplitudes. Then, they were tested monotonically to failure under four-point-bending. The test results provide an insight on the fatigue and post-fatigue behaviour of FOS used for monitoring reinforced concrete structures.

A sizeable number of efforts have sought to instrument bridges for the purpose of structural monitoring and assessment. The outcomes of these efforts, as gaged by advances in the understanding of the definition of structural damage and their role in sensor selection as well as in the design of cost and data-effective monitoring systems, has itself been difficult to assess. The authors' experience with the design, construction, and operation of a monitoring system for the south-bound Kishwaukee Bridge has provided several lessons that bear upon these concerns. In this paper we describe certain aspects of the design of our Unix-based monitoring system. The system, patterned after similar systems developed for kick detection and well-control in the oil industry, has performed well in providing a continuous, low-cost monitoring platform for bridge engineers with immediately relevant information.

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.

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.

Excimer laser ablation utilized in artwork restoration generates pressure waves that may influence the structural integrity. By means of holographic interferometry a non- destructive highly sensitive mapping for evaluating the structural state is provided. The long-term sequential recording enables comparison between time resolved optical wave fronts scattered from the artwork before and after the selective ablation of material. Thus, comparative structural monitoring of laser-induced photomechanical effects that may result in potential damage of the artwork is accomplished.

This presentation examines some examples of aerospace demonstration of structural monitoring sensors from one `end-user' company perspective. Some of the key hurdles yet to be surmounted are also identified.

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.

For many structural applications it is highly desirable to be able to measure two or more axes of strain at a single point. In many cases one dimensional strain measurements may be insufficient to fully characterize events or lead to erroneous predictions. This paper will provide an overview of the use of multi-axis fiber grating strain sensors to perform structural diagnostics. Examples of usage of multi-axis fiber grating strain sensors in a smart bearing cell for damage assessment of bridges and for adhesive joints associated with aircraft will be given as illustrations of these methods.

In order to increase the safety of the civil engineering structures many different systems for their auscultation are developed. The majority of these systems are based on measurement of strain, deformation or displacement.

There are approximately 576,000 major bridges, 3.2 billion square feet of bridge deck, and 162,000 miles of highways making up a part of the civil infrastructure system in the United States. Fiber grating strain sensors have the ability to play an important role in the health monitoring of these structures. The advantages of fiber optic sensors including EMI resistance, unobtrusive size, multiplexing/distributed capabilities, and environmental ruggedness, make them a logical choice for structural monitoring.

A basic step in the monitoring of health of any structure is detection of damage levels and location of the damage in the system. Several damage detection schemes have been proposed in recent years. Published applications of these methods are typically for simplified models of realistic structures. This leaves open the question of the accuracy and efficiency of the available damage detection methods when applied to large and complex structural models. This paper will investigate the accuracy of different damage detection techniques to complex structural models. A typical multi- jointed steel bridge, which is damaged by cracks of different sizes, is considered. The damage will be simulated analytically in the structural model, and the damage detection algorithms will be applied to both the damaged and the undamaged structures. Three damage detection algorithms are investigated, namely the change of stiffness, the change of flexibility and the damage index methods. Some modifications and extensions of the change of stiffness and change of flexibility methods were incorporated in this study. These extensions helped inaccurate comparisons between different methods. It was found that all three algorithms produced adequate damage detection results. More analytical studies are recommended. Also, experimental testing for complex structures is recommended.

Optical fibre sensors have enormous potential as an important technology in structural monitoring. Their particular advantages include the ability to make distributed measurements, immunity from electromagnetic noise and pick-up and the capability of operating over large areas and/or at interrogation distances of many kilometres. This paper will, first of all, examine the requirements for structural monitoring in both civil engineering and composite structures for aerospace and underground transportation. The benefits and disadvantages of fibre optic techniques will then be explored and the general features of important contributory technologies including fibre Bragg gratings, microbend sensing, interferometric and sub-carrier sensors and non-linear optical techniques, e.g. stimulated Brillouin scatter will be highlighted and their applications and properties described. The paper then examines some specific applications in each of these two principal sectors and concludes by speculating on future prospects for fibre optic sensing and structural assessment.

A novel optical fiber sensor implementation for monitoring structural displacement and load is explored. This new sensor makes use of simple coupling losses between fibers in a hollow core sleeve, and as such, offers variable sensitivity, ruggedness, and design flexibility. Preliminary test results show promise towards the goal of making practical and cost effective fiber optic sensors for field use in structural monitoring. In addition to hardware tests, a computer simulation was written to model sensor performance, and critical design parameters were identified.

This paper describes an instrumentation technique for 'reading' multiple fiber Bragg grating strain sensors, and focuses on a prototype system designed and built for the FHWA for multipoint monitoring of strain in concrete structures.

This paper will present a brief overview of the current activities in fiber optic distributed, integrating and quasi distributed measurements within the University. The research focuses on applications in structural monitoring and includes a distributed moisture ingress monitor and some simple systems exploiting special cable structures to implement specialized strain and distance measurement for self surveying structures.

A new methodology has been developed for structural damage assessment and monitoring based on smart material sensors. The sensors transform to a ferromagnetic phase progressively as afunction of strain. The solid-state phase transformation is useful in determining the localstructural peak strains in monitored high stress sites. The technology is discussed with applications provided to illustrate the utility of the approach in addressing a range of engineering problems. Introduction Structural health monitoring of the aging infrastructure has become a major concern throughout the world. The desire to extend the lives of engineering structures beyond their intended design lifetimes has to be carefully weighed against the possible risks to public safety. Clearly, the economic reality is that most countries simply cannot afford to replace all of thestructures which have reached the end of their respective design lives. With careful and cautious structural monitoring it is possible to safely extend useful service life well beyond the

This paper looks at the real problems facing engineers today when assessing the durability of structures. The role of monitoring structures to assess their current and long term behavioral characteristics and the enhancement of the safe use of structures is discussed. The capability of existing sensor systems to enable structures to inform engineers as to the onset of problems occurring is highlighted, thus establishing the advent of Smart Structures as a reality of today, rather than an idea of the future.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A measuring system adapted to the needs of civil engineering structural monitoring is presented. It is based on low coherence interferometry in standard singlemode fibers and has a resolution of 5 micrometers , an operational range of 7 cm, stability over long periods (at least 1 year) and insensitivity to variations of the fiber losses. The portable reading unit doesn't need to be connected to the sensing fibers permanently and can thus be used to monitor multiple structures reducing the costs of the instrumentation. This paper presents the operating principle of this system and different techniques used to install the sensing fibers in large concrete structures, timber and mixed timber-concrete structures as well as on metals.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The potential use of optical fiber sensors embedded, prior to curing, in reinforced concrete buildings and in structures such as bridges, dams and tanks is discussed with regards to the non-destructive measurement of internal strain, and the evaluation of structural integrity. Novel applications in the areas of structural monitoring, experimental stress analysis and in the management and control of service installations are presented. A discussion of the fundamental issues regarding the practical implementation of this technology is given.

Current and projected advances in aerospace structures technology for such programs as the Advanced Tactical Fighter, Orient Express, and NASA space platforms are used as the starting point for a top-level structural monitoring systems analysis. Performance requirements are considered for such structures, and used to identify needs for integral sensors and systems. Implications of recent work are discussed, which have demonstrated the potential for fiber optic sensor systems which can assess and report on structural condition in real time. The essential system elements are defined, and constraints imposed by vehicle environments are considered. The resulting development needs, for fiber optic sensors and systems are stated in the conclusion.