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Truly Distributed Optical Fiber Sensors for Structural Health Monitoring: From the Telecommunication Optical Fiber Drawling Tower to Water Leakage Detection in Dikes and Concrete Structure Strain Monitoring  [PDF]
Jean-Marie Henault,Gautier Moreau,Sylvain Blairon,Jean Salin,Jean-Robert Courivaud,Frédéric Taillade,Erick Merliot,Jean-Philippe Dubois,Johan Bertrand,Stéphane Buschaert,Stefan Mayer,Sylvie Delepine-Lesoille
Advances in Civil Engineering , 2010, DOI: 10.1155/2010/930796
Abstract: Although optical fiber sensors have been developed for 30 years, there is a gap between lab experiments and field applications. This article focuses on specific methods developed to evaluate the whole sensing chain, with an emphasis on (i) commercially-available optoelectronic instruments and (ii) sensing cable. A number of additional considerations for a successful pairing of these two must be taken into account for successful field applications. These considerations are further developed within this article and illustrated with practical applications of water leakage detection in dikes and concrete structures monitoring, making use of distributed temperature and strain sensing based on Rayleigh, Raman, and Brillouin scattering in optical fibers. They include an adequate choice of working wavelengths, dedicated localization processes, choices of connector type, and further include a useful selection of traditional reference sensors to be installed nearby the optical fiber sensors, as well as temperature compensation in case of strain sensing. 1. Introduction Specifications for large-sized engineering structures such as the Rion-Antirion bridge (Greece) or the Millau viaduct (France) now commonly include instrumentation in order to address monitoring requirements, not only during the construction period, but also to allow lifetime structural health monitoring. EDF’s (French Electricity Company) potential applications include dams, dike and power plant reactors monitoring. Andra’s (French National Radioactive Waste Management Agency) potential applications include surface and deep geological radioactive waste disposal structure monitoring, for instance, within the future geological repository that would contain highly instrumented disposal cells. LCPC is in charge of the surveillance of various French bridges developing structural pathologies due to aging. Controlling the state of a structure's health, more commonly designated by the acronym SHM (Structural Health Monitoring), requires a large number of sensors. For this application, optical fiber sensors [1] (OFS) are found to be exceptional tools, especially as they enable distributed measurements [2] thus providing data over the entire structure instead of being limited to point data at sensor locations. Monitoring with a single fiber can thus provide information of the overall structure behavior, and thus overcome limitations of traditional sensors, whose information is restricted to local effects. Some 20 years of developments have been necessary to overcome the initial disappointments and fully
Modal macro-strain identification from operationalmacro-strain shape under changing loading conditions  [PDF]
Li Shu, Xu Zhaodong, , Wang Shaojie, Wu Zhishen
- , 2016, DOI: 10.3969/j.issn.1003-7985.2016.02.015
Abstract: To develop modal macro-strain(MMS)identification techniques and improve their applicability in a continuous health monitoring system for civil infrastructures, the concept of operational macro-strain shape(OMSS)and the corresponding identification method are proposed under unknown ever-changing loading conditions, and the MMS is then obtained. The core of the proposed technique is mainly based on the specific property that the macro-strain transmissibility tends to be independent of external excitations at the poles of the system and converges to a unique value. The proposed method is verified using the experimental data from a three-span continuous beam excited by an impact hammer at different locations. The identified results are also compared with the commonly used methods, such as the peak-picking(PP)method, the stochastic subspace identification(SSI)method, and numerical results, in the case of unknown input forces. Results show that the proposed technique has unique merits in accuracy and robustness due to its combining multiple tests under changing loading conditions, which also reveal the promising application of the distributed strain sensing system in identifying MMS of operational structures, as well as in the structural health monitoring(SHM)field.
Distributed Strain Sensor Networks for In-Construction Monitoring and Safety Evaluation of a High-Rise Building
X. W. Ye,Y. Q. Ni,Y. X. Xia
International Journal of Distributed Sensor Networks , 2012, DOI: 10.1155/2012/685054
Abstract: The New Headquarters of Shenzhen Stock Exchange (NHSSE), currently being constructed in Shenzhen, China, is a high-rise building with a height of 245 m. One salient feature of NHSSE is its huge floating platform with an overall plan dimension of and a total height of 24 m, making it one of the largest cantilever structures in the world. In recognition of the uniqueness of the floating platform, a long-term structural health monitoring (SHM) system has been designed and implemented by The Hong Kong Polytechnic University for both in-construction and in-service monitoring of NHSSE. As part of this monitoring system, 224 vibrating-wire strain gauges have been permanently installed to measure the strain responses of key structural components of the floating platform. A wireless strain monitoring system by integrating local tethered data acquisition and long-range wireless data transmission has been developed for real-time strain monitoring and visualization. This paper presents the stress evolution of the floating platform during dismantlement of temporary supports on the basis of the real-time monitoring data and the statistical stress analysis and safety evaluation of the floating platform by use of the long-term monitoring data, as well as the effect of the welding residual stress on structural safety of NHSSE.
Distributed Strain Measurement along a Concrete Beam via Stimulated Brillouin Scattering in Optical Fibers  [PDF]
Romeo Bernini,Aldo Minardo,Stefano Ciaramella,Vincenzo Minutolo,Luigi Zeni
International Journal of Geophysics , 2011, DOI: 10.1155/2011/710941
Abstract: The structural strain measurement of tension and compression in a 4 m long concrete beam was demonstrated with a distributed fiber-optic sensor portable system based on Brillouin scattering. Strain measurements provided by the fiber-optic sensor permitted to detect the formation of a crack in the beam resulting from the external applied load. The sensor system is valuable for structural monitoring applications, enabling the long-term performance and health of structures to be efficiently monitored.
A Practical Monitoring System for the Structural Safety of Mega-Trusses Using Wireless Vibrating Wire Strain Gauges  [PDF]
Hyo Seon Park,Hwan Young Lee,Se Woon Choi,Yousok Kim
Sensors , 2013, DOI: 10.3390/s131217346
Abstract: Sensor technologies have been actively employed in structural health monitoring (SHM) to evaluate structural safety. To provide stable and real-time monitoring, a practical wireless sensor network system (WSNS) based on vibrating wire strain gauges (VWSGs) is proposed and applied to a building under construction. In this WSNS, the data measured from each VWSG are transmitted to the sensor node via a signal line and then transmitted to the master node through a short-range wireless communication module (operating on the Industrial, Scientific, and Medical (ISM) band). The master node also employs a long-range wireless communication module (Code Division Multiple Access—CDMA) to transmit the received data from the sensor node to a server located in a remote area, which enables a manager to examine the measured data in real time without any time or location restrictions. In this study, a total of 48 VWSGs, 14 sensor nodes, and seven master nodes were implemented to measure long-term strain variations of mega-trusses in an irregular large-scale building under construction. Based on strain data collected over a 16-month period, a quantitative evaluation of the construction process was performed to determine the aspects that exhibit the greatest influence on member behavior and to conduct a comparison with numerical simulation results. The effect of temperature stress on the structural elements was also analyzed. From these observations, the feasibility of a long-term WSNS based on VWSGs to evaluate the structural safety of an irregular building under construction was confirmed.
Multiscale Acceleration-Dynamic Strain-Impedance Sensor System for Structural Health Monitoring  [PDF]
Duc-Duy Ho,Khac-Duy Nguyen,Han-Sam Yoon,Jeong-Tae Kim
International Journal of Distributed Sensor Networks , 2012, DOI: 10.1155/2012/709208
Abstract: A multiscale wireless sensor system is designed for vibration- and impedance-based structural health monitoring. In order to achieve the objective, the following approaches are implemented. Firstly, smart sensor nodes for vibration and impedance monitoring are designed. In the design, Imote2 platform which has high performance microcontroller, large amount of memory, and flexible radio communication is implemented to acceleration and impedance sensor nodes. Acceleration sensor node is modified to measure PZT’s dynamic strain along with acceleration. A solar-power harvesting unit is implemented for power supply to the sensor system. Secondly, operation logics of the multi-scale sensor nodes are programmed based on the concept of the decentralized sensor network. Finally, the performance of the multi-scale sensor system is evaluated on a lab-scale beam to examine the long-term monitoring capacities under various weather conditions. 1. Introduction Many researchers have developed novel sensing technologies for the practical structural health monitoring (SHM) applications. The SHM system for civil infrastructures mainly includes a number of sensors, a huge amount of signal transmitting wires, data acquisition instruments, and centralized data storage servers [1–3]. Also, the stored data in the centralized servers should be handled for offline information analysis. In order to reduce high-tech labors and costs associated with the wired SHM system, many researchers have attempted to adopt wireless sensors [4–10]. One of great advantages for using wireless sensors is autonomous operations for SHM, which can be implemented by embedding system technologies. The development of wireless sensor nodes as much as the selection of embedding SHM algorithms are important topics for the autonomous SHM [11–15]. To date, many damage monitoring algorithms have been developed for detecting the location and the severity of damage in structures [16–20]. Most of those algorithms are dependent on structural types, damage characteristics, and available response signals that are related to external loadings and environmental conditions. Since 1990s, several researchers have focused on using vibration characteristics of a structure as an indication of its structural damage [21–24]. Acceleration response of a structure is usually measured to obtain modal parameters such as natural frequency and mode shapes which are utilized for damage detection. It were demonstrated that curvature (or strain) mode shapes are sensitive to structural damage in beam structures [19]. However,
Bridge Assessment and Health Monitoring with Distributed Long-Gauge FBG Sensors  [PDF]
Chunfeng Wan,Wan Hong,Jianxun Liu,Zhishen Wu,Zhaodong Xu,Shu Li
International Journal of Distributed Sensor Networks , 2013, DOI: 10.1155/2013/494260
Abstract: Most sensors for structural testing and health monitoring are “point” sensors which strongly limit the ability to correct damage detection and structural assessment. In this paper, long-gauge FBG sensor which can sense the whole area within the gauge length is introduced. Bridge assessment and health monitoring with the microstrain distribution acquired by the distributed long-gauge FBG sensor are also studied. Experiments were conducted and application to a real prestressed box bridge was also implemented. Static and dynamic testing results show that distributed long-gage FBG sensing technique can obtain not only the global information such as bridge deflection and natural frequency, but also the local parameters such as strain and modal macrostrain to detect damage of the bridge. It shows that structural assessment and health monitoring based on the proposed technique have great potential in maintenance of civil engineering infrastructures. 1. Introduction Bridges are the most important facilities for many cities and countries. These infrastructures provide the necessary communication and transportation conditions for the residence. However, progressive deterioration of the civil infrastructure begins once they are built and subjected to normal continuous and occasional excessive loading, or adverse environmental conditions. For the purpose of protecting and maintaining these infrastructures, prompt and intensive monitoring of structural system becomes extremely important. Nowadays, most Structural Health Monitoring (SHM) research has focused either on global damage assessment techniques using structural dynamic responses or on limited local independent damage detection mechanisms. Vibration-based global SHM using typical acceleration measurements still faces some challenges for the reason that structural modal parameters seem too “global” to detect the damage that is an intrinsically local phenomenon in structures. On the other hand, although relatively reliable, local inspections are cost, labor-intensive, and too “local” to obtain the integrated information for the overall structure. Under this background, the concept of distributed long-gage FBG sensing techniques, which is dedicated to catching and utilizing the strain distribution throughout the full or some partial areas of structures to detect damage, has been proposed to develop an integrated SHM strategy [1]. As a typical local measurement, strain has been verified to be very sensitive to damage. However, for the health monitoring of large-scale civil structures, strain measurement always
Distributed Strain Measurement along a Concrete Beam via Stimulated Brillouin Scattering in Optical Fibers  [PDF]
Romeo Bernini,Aldo Minardo,Stefano Ciaramella,Vincenzo Minutolo,Luigi Zeni
International Journal of Geophysics , 2011, DOI: 10.1155/2011/710941
Abstract: The structural strain measurement of tension and compression in a 4?m long concrete beam was demonstrated with a distributed fiber-optic sensor portable system based on Brillouin scattering. Strain measurements provided by the fiber-optic sensor permitted to detect the formation of a crack in the beam resulting from the external applied load. The sensor system is valuable for structural monitoring applications, enabling the long-term performance and health of structures to be efficiently monitored. 1. Introduction Structural health monitoring systems have the potential to reduce operational maintenance costs by identifying problems at an early stage, and to verify the effectiveness of repair procedures. Moreover, monitoring systems help increase understanding of the real behavior of a structure, such as a bridge, and aid in planning maintenance interventions. In the long term, static monitoring requires an accurate and very stable system, which can relate deformation measurements taken over long periods of time [1]. Strain measurement with a distributed Brillouin scattering-based sensor system provides excellent opportunity for the health monitoring of civil structures [2–4]. It allows measurements to be taken along the entire length of the fiber, rather than at discrete points, by using fiber itself as the sensing medium. Distributed optical fiber sensors based on stimulated Brillouin scattering (SBS) rely on the interaction between two lightwaves and an acoustic wave in the optical fiber. The measurement principle is based on the characteristic that the Brillouin frequency of the optical fiber is shifted when strain as well as temperature changes occur. Spatial information along the length of the fiber can be obtained through Brillouin optical time domain analysis (BOTDA) by measuring propagation times for light pulses travelling in the fiber. This allows for continuous distributions of the measurand to be monitored. This type of sensing has tremendous potential for structural monitoring. These systems offer unmatched flexibility of measurement locations and the ability to monitor a virtually unlimited number of locations simultaneously. In this paper, we report a number of experimental measurements carried out along a 4?m-long concrete beam subjected to a variable load, by the use of a portable BOTDA sensor. A single-mode optical fiber was attached to the beam in order to detect both tensile and compressive strains. Two different adhesives were employed, in order to compare them as regards their efficiency in transferring the strain between the
Industrial Qualification Process for Optical Fibers Distributed Strain and Temperature Sensing in Nuclear Waste Repositories  [PDF]
S. Delepine-Lesoille,X. Phéron,J. Bertrand,G. Pilorget,G. Hermand,R. Farhoud,Y. Ouerdane,A. Boukenter,S. Girard,L. Lablonde,D. Sporea,V. Lanticq
Journal of Sensors , 2012, DOI: 10.1155/2012/369375
Abstract: Temperature and strain monitoring will be implemented in the envisioned French geological repository for high- and intermediate-level long-lived nuclear wastes. Raman and Brillouin scatterings in optical fibers are efficient industrial methods to provide distributed temperature and strain measurements. Gamma radiation and hydrogen release from nuclear wastes can however affect the measurements. An industrial qualification process is successfully proposed and implemented. Induced measurement uncertainties and their physical origins are quantified. The optical fiber composition influence is assessed. Based on radiation-hard fibers and carbon-primary coatings, we showed that the proposed system can provide accurate temperature and strain measurements up to 0.5?MGy and 100% hydrogen concentration in the atmosphere, over 200?m distance range. The selected system was successfully implemented in the Andra underground laboratory, in one-to-one scale mockup of future cells, into concrete liners. We demonstrated the efficiency of simultaneous Raman and Brillouin scattering measurements to provide both strain and temperature distributed measurements. We showed that 1.3?μm working wavelength is in favor of hazardous environment monitoring. 1. Introduction Distributed optical fiber sensors (OFSs) [1–3] are a key technology for the monitoring of the planned French deep geological repository for long-lived high-level and intermediate-level wastes, called Cigéo. Temperature and strain distributed sensing based on Raman, Rayleigh, and Brillouin scatterings offer exceptional advantages over traditional electronic sensors, especially as they provide distributed data over the entire structure and thus overcome limitations of traditional sensors, whose information is restricted to local effects. This paper focuses on temperature and strain distributed sensing based on Raman and Brillouin scatterings in optical fibers for structural health monitoring, more precisely for nuclear industry. Although commercial off-the-shelf sensors and interrogation units are numerous, the global measuring chain may provide disappointing monitoring results to the end-users, unless a number of considerations specific to nuclear environments are taken into account. These are further developed within this paper, with an emphasis on environmental conditions influence, especially (i) temperature, (ii) gamma rays, and (iii) hydrogen influences. Andra’s (French National Radioactive Waste Management Agency) potential applications include surface and deep geological radioactive waste disposal structure
Vibration-based structural health monitoring technique using statistical features from strain measurements  [PDF]
A.P. Adewuyi,Z.S. Wu
Journal of Engineering and Applied Sciences , 2009,
Abstract: A statistical vibration-based damage identification algorithm to assess the stability of the measurement data, detect and locate damage in civil structures, where variability in response and modal parameters due to measurement noise and environmental influence is often inevitable, is presented in this paper. The method exploits the regression analysis of peak values of the magnitudes of frequency response function (FRF) of target sensors relative to the reference wherein the statistical features are employed for data reliability assessment and damage localization. Through experimental investigation of a flexural structure using conventional strain gauges and long gauge fiber Bragg gratings (FBG) sensors, the importance of the technique for civil SHM is established and presented in an easy-to-interpret graphical format for effective implementation of results. The statistical approach is very effective for damage localization using strain data.
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