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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 sensin...
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... Bragg grating is a periodic variation of refractive index along the length of the fiber, normally about 10 mm in total length. Gratings with periods K are commonly fabricated by holographic [73] or phasemask technique [41,79]. The working principle of the Bragg grating sensor is shown in Fig. 3. When a broadband or tunable signal passes through the optical fiber, the wavelength corresponding to the period of index variation (k B ) will be preferentially reflected. The relationship between Bragg wavelength and the periodic spacing of the grating is given by Eq. 1 ...
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... makes the structure aesthetically attractive but extremely complex in structural behaviors, especially the wind-structure interaction. Even the wind characteristic at the top level of the building cannot be reliably obtained. 120 FBG strain and temperature sensors were installed in GNTVT at 5 different levels for in-service monitoring as shown in Fig. 23 [75]. Specially packaged FBG strain sensors were welded on the surface of the structural steel of the outer tube columns in factory to measure both cumulative and dynamic strain. The sensors were packaged in a specially designed steel cage to prevent damage during welding. At each level, 24 FBG sensors were attached in 4 separated ...
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... intensity is measured, this method can overcome the instability problems caused by decrease of the indicator concentration due to photodegradation or leaching out, drifts of the light source intensity as well as bending of optical fibers. The sensor consists of a fiber bundle, a glass window, a pH sensitive membrane and a reflective layer (Fig. 30). The fiber bundle maximizes the intensity of light transmission. When pH level changes, the absorbed wavelength of the pH sensitive membrane also changes. The absorption spectrum is measured by a spectrometer. The sensor was used to monitor steel anchor corrosion to avoid bond failure with the fixed anchorage length [33]. The sensitive ...
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... is switched off, the reference point is lost. So, the conventional configuration of EFPI may not be suitable candidate of long term static measurement. A dual-EFPI pressure sensor that could specify a stable zero-point for every intermittent measurement was therefore developed [25,26]. One EFPI is for measurement and the other is for triggering (Fig. 32). The self-calibration procedure is started by applying compressed air to the head so that the elastic element is slightly deformed to reach a well defined reference position, which is detected by the triggering EFPI. Then, the head is bounced back to the measuring EFPI by the elastic element. The diaphragm displacement is obtained from ...
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... sensors to acquire adequate monitoring results, which is impractical and uneconomical. Distributed sensor provides an alternative. Geotextile is commonly used in retaining structures for reinforcement and drainage. An instrumented geotextile integrated with telecommunication silica single mode optical fiber was embedded into embankments or dikes (Fig. 33). Displacement was calculated from the distributed strain along the optical fiber obtained from stimulated Brillouin scattering measured by Brillouin optical time domain reflectometry/analysis [33,67,76] or Brillouin optical frequency domain analysis (BOFDA) [34]. The cost of BOFDA is potentially lower than BOTDA. However, the ultimate ...
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... slope, it is difficult to embed instrumented geotextile to monitor the displacement profile. Instead, a FBG based self temperature compensated in-place inclinometer was developed and installed at a road side slope at Luk Keng Road, Sheung Shui, Hong Kong [78,107]. Several instrumented segments are embedded in a polyvinyl chloride (PVC) casing (Fig. 34). The outer and inner diameters of the PVC casing are 70 and 60 mm, respectively. Each instrumented segment consists of a deformable tube of about 1.5 m long, which is made of polycarbonate (PC), fixed at two ends by rigid stainless steel tubes. The position of the stainless steel tubes are guided by two pairs of sliding wheels, which ...
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... fiber Fig. 33 Schematic diagram of instrumented geotextile for monitoring displacement of retaining structures (Fig. 35). The steel tube and steel wires provided mechanical protection while the polymer sheath protected the steel from corrosion. The sensor could operate over large temperature ranges by employing appropriate coating of the optical ...
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... fiber Fig. 33 Schematic diagram of instrumented geotextile for monitoring displacement of retaining structures (Fig. 35). The steel tube and steel wires provided mechanical protection while the polymer sheath protected the steel from corrosion. The sensor could operate over large temperature ranges by employing appropriate coating of the optical fiber. The optical fiber was long enough to avoid any tensile strain, and hence, only thermal induced strain ...
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... hydropower plant on the Daugava River in Lativa was 40 years old. The joint between two adjacent blocks of the dam was sealed by bitumen. The abrasion of the joints might redistribute the loading on tape with 0.20 mm thickness and 13.0 mm width was attached on concrete surface (Fig. 36). Additional loose fiber embedded in steel tube with plastic sheath (Fig. 35) was installed in parallel to measure the distributed temperature from the stimulated Brillouin scattering for compensation of the strain measured by the sensing tape [51]. Water leakage may change the moisture content of surrounding soil. An OFS was developed ...
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... plant on the Daugava River in Lativa was 40 years old. The joint between two adjacent blocks of the dam was sealed by bitumen. The abrasion of the joints might redistribute the loading on tape with 0.20 mm thickness and 13.0 mm width was attached on concrete surface (Fig. 36). Additional loose fiber embedded in steel tube with plastic sheath (Fig. 35) was installed in parallel to measure the distributed temperature from the stimulated Brillouin scattering for compensation of the strain measured by the sensing tape [51]. Water leakage may change the moisture content of surrounding soil. An OFS was developed to measure the absorption spectrum of evanescent field as the existence of ...
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... to pinpoint the exact leak location, so slow and expensive visual inspection needs to be undertaken. It is impractical to apply point sensors for monitoring these kinds of structures. Several distributed sensors based on Brillouin optical time domain thermoplastic tape polyimide optical fiber 145 microns diameter 13 mm width, 0.2 mm thickness Fig. 36 Schematic diagram of surface-mounted sensor for distributed strain measurement reflectometry (BOTDR) have therefore been developed. To measure the deflection of the pipeline, the tapes shown in Fig. 36 were glued along the whole length of a pipeline in Rimini of Italy at 0°, 30° and 150° from the longitudinal direction [51,52]. An ...
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... sensors based on Brillouin optical time domain thermoplastic tape polyimide optical fiber 145 microns diameter 13 mm width, 0.2 mm thickness Fig. 36 Schematic diagram of surface-mounted sensor for distributed strain measurement reflectometry (BOTDR) have therefore been developed. To measure the deflection of the pipeline, the tapes shown in Fig. 36 were glued along the whole length of a pipeline in Rimini of Italy at 0°, 30° and 150° from the longitudinal direction [51,52]. An additional optical fiber was placed inside a stainless steel loose tube (as in Fig. 35) and it was mounted along the longitudinal direction of the pipeline for temperature measurement. The strain resolution ...
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... measurement reflectometry (BOTDR) have therefore been developed. To measure the deflection of the pipeline, the tapes shown in Fig. 36 were glued along the whole length of a pipeline in Rimini of Italy at 0°, 30° and 150° from the longitudinal direction [51,52]. An additional optical fiber was placed inside a stainless steel loose tube (as in Fig. 35) and it was mounted along the longitudinal direction of the pipeline for temperature measurement. The strain resolution was about 20 microstrains with spatial resolution of 1.5 m. The temperature resolution was about 1 °C with similar spatial resolution. The distributed strain after temperature compensation can be used to monitor the ...
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... the Brillouin fiber sensor (about 15 cm). In this case, the Brillouin frequency spectrum shows multiple peaks and the measured strain is underestimated by commonly used single peak fitting method. By using multiple-peak fitting, the maximum tensile or compressive strain is captured in about one-third of the spatial resolution (5 cm) as shown in Fig. 37 ...
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... to monitor the buckling of the pipeline was demonstrated in [81, Fig. 37 Comparison between multiple-peak and single-peak fitting methods to extract the strain distribution from a Brillouin frequency spectrum 82,110]. Several telecommunication silica optical fibers were attached on the circumference of pipeline along the longitudinal direction (Fig. 38). By using the coherent probe-pump based Brillouin sensor [108], centimeter spatial resolution and 15 microstrains accuracy can be achieved over tens of ...
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... on the scale of the maps of the cable route. The accuracy of this conventional method is only around 40-50 m. By using the BOTDR, approximate fault location can be identified. Then, the cable was lifted (about 100 m in length) and heated up by 5 °C locally, the distance between the heating and fault locations can be measured [69]. As shown in Fig. 39, by comparing the BOTDR reading between the preheated and heated strain distribution, the distance between the heated up point and the fault location can be estimated precisely. By using this technique, the accuracy of fault location can reach the spatial resolution of the BOTDR. In this paper, the basic principles of commonly used OFS ...
Citations
... Fiber optic sensors have the advantages of compact structure, high sensitivity, and strong resistance to electromagnetic interference. They can be widely used in aerospace, petroleum, chemical, and other industrial fields for the measurement of physical parameters such as temperature, pressure, and strain [1] . Currently, commonly used fiber optic sensors include fiber Bragg gratings (FBGs) [2] , Fabry-Perot interferometers (FPIs) [3] , long-period fiber gratings (LPFGs) [4] , and Mach-Zehnder interferometers (MZIs) [5] . ...
... Recently, Pitawala et al. (2022) demonstrated the application of distributed fibre optic sensors to foamed bitumen stabilised pavement beams in order to characterise their flexural behaviour in the laboratory while using a technique based on Rayleigh scattering as in the present study. A broader picture about recent applications of fibre optic sensors in pavements is provided within the study of De Maeijer et al. (2019), more general applications in civil engineering are reported e.g. in Leung et al. (2015) and an overview of the various fibre optic sensor technologies is provided e.g. by Hartog (2017) or Thévenaz (2011). ...
Understanding the in-situ structural behaviour of pavements plays an important role in road engineering. Hence, various measurement methods were developed in the past to get an insight into the response of roads to traffic loading. In the present study, distributed fibre optic strain sensors were embedded into a hot mix asphalt pavement. The sensors were used for strain measurements with high spatial resolution in order to assess its feasibility to gain the continuous strain distribution in the pavement under short-term static loading. In addition, the loading process was measured with high temporal resolution, indicating that-using shorter sensor lengths-vehicle passages could also be studied. The strain distributions gathered with this type of sensor were compared to the results of a simple finite element model and the effect of applying various sensor cables. In addition, new opportunities provided by distributed fibre optic sensors in road engineering are discussed. ARTICLE HISTORY
... Over the years, many technologies have been developed to characterize damages in concrete infrastructures. These can be classified based on the sensing principle utilized: stress waves [1,2], electrical properties [3,4], optical fibers [5,6], or digital image correlation (DIC) [7]. Among these techniques, the vision-based technique is considered apt because of its simple implementation as well as direct and easy result interpretation. ...
In this paper, we introduce SHSnet, an advanced deep learning model designed for the efficient end-to-end segmentation of complex cracks, including thin, tortuous, and densely distributed ones. SHSnet features a non-uniform attention mechanism, a large receptive field, and boundary refinement to enhance segmentation performance while maintaining computational efficiency. To further optimize the model’s learning capability with highly imbalanced datasets, we employ a loss function (LP) based on the focal Tversky function. SHSnet shows very high performance, with values of 0.85, 0.83, 0.81, and 0.84 for precision, recall, intersection over union (IOU), and F-score, respectively. It achieves this with 10× fewer parameters than other models in the literature. Complementing SHSnet, we also present the post-processing unit (PPU), which analyzes crack morphological parameters through fracture mechanics and geometric properties. The PPU generates scanning lines to accurately compute these parameters, ensuring reliable results. The PPU shows a relative error of 0.4%, 1.2%, and 5.6% for crack number, length, and width, respectively. The methodology was benchmarked on complex ECC crack datasets as well as on multiple online datasets. In both of these cases, our results confirm that SHSnet consistently delivers superior performance and efficiency across various scenarios as compared to the methods in the literature.
... As the field continues to evolve, interdisciplinary collaborations between engineering, optics, materials science, and geology are likely to drive further innovations in research and practical implementations. In the past 35 years, DFOS technology has been applied to the monitoring of pipelines, slopes, tunnels, foundations, and other engineering projects [72,73]. Meanwhile, relevant model tests and feasibility studies have also been continuously carried out [74][75][76]. ...
DFOS (distributed fiber-optic sensing) technology has shown the potential to increase the accuracy of measurement after years of development and experimenting in geoengineering monitoring. To better understand the development of DFOS technology and its contribution to geoengineering, an objective and data-driven review of the development process of DFOS technology in construction was completed. The review was accomplished by using text mining methods on the Web of Science, covering a wide range of relevant data, including 3970 articles from 1989 to 2023. The results indicate that DFOS technology research demonstrates the typical characteristics of multi-author, multi-country, and multi-institution collaborations, spanning various research fields. Over the past 35 years, the number of published articles has exhibited exponential growth, with China making significant contributions and leading in terms of its total publication growth rate, which has been higher than that of the United States since 2016. In the analysis of author keywords, emerging technologies, such as machine learning and distributed acoustic sensing, have garnered attention. The findings contribute to a comprehensive understanding of the development, impact, and future trends of DFOS technology in geotechnical engineering, offering valuable insights for researchers, scholars, and students in the field and inspiring new approaches for research methods in this domain.
... [3][4][5][6][7][8][9]. Fiber sensors can be implemented to monitor structures, pipelines, oil and gas reservoirs, wellbores, as well as temperature changes in dams and permafrost [4,[9][10][11][12]. They can be applied to rail-track monitoring, detection of earthquakes and water swells, and load displacement monitoring in mines [4,10,[12][13][14][15]. ...
... Fiber sensors can be implemented to monitor structures, pipelines, oil and gas reservoirs, wellbores, as well as temperature changes in dams and permafrost [4,[9][10][11][12]. They can be applied to rail-track monitoring, detection of earthquakes and water swells, and load displacement monitoring in mines [4,10,[12][13][14][15]. Thus, fiber sensors can play a role in preventing and mitigating the social, economic, and environmental costs of accidents and natural disasters. ...
We demonstrate an optical fiber sensor that uses the orbital angular momentum of light in a polarization maintaining fiber to act as a temperature and force sensor. The polarization of the input light is shown to greatly affect the sensitivity of the sensor. In addition, we show how our sensor can be used to resolve the direction and magnitude of a force applied to a fiber.
... For instance, the use of electromagnetic equipment plays a crucial role in assessing the performance of concrete structures equipped with sensors and actuators [36,37]. These systems commonly incorporate smart materials such as memory alloys [38][39][40], piezoelectric materials [41][42][43], and optical fibers [44][45][46][47], marking an important step towards the development of smart materials. ...
This research experimentally assessed the compressive strength enhancement of 7- and 28-day concrete specimens with up to 20 % silica sand and micro silica under an alternating magnetic field up to 1 Tesla. By applying magnetic fields to hardened concrete, properties can be tailored to specific needs, thus lowering cement usage and CO2 production. It was found that adding 10 % micro silica reduced the compressive strength at 7 and 28 days, while using 10 % silica sand and 5 % micro silica increased the compressive strength by 14.55 % and 7.79 %, respectively. Exposing specimens to a magnetic field increased compressive strength, with improvements up to 60.36 % for 7-day and 48.02 % for 28-day concrete at 1 T. Incorporating silica sand and micro silica in concrete positively impacts compressive strength under a magnetic field. Silica sand enhances compatibility with additives, improving strength. However, substituting 10 % of cement with micro silica reduces strength due to decreased aggregate adherence. 7-day specimens are more susceptible to magnetic fields than 28-day specimens due to lower displacement in younger samples. This innovative method enables controlled material behavior under magnetic influence. It aims to reduce cement usage while compensating for strength reduction caused by micro silica substitution. The study also determines the minimum magnetic field needed to counteract strength decrease; the aspects which not previously explored.
... More significantly, although two spans of cables (H-and Tcables) were assumed to embed parallel with the help of cable guides, a slight variance in the temperature change was observed (a case of 2.4 W/m in Fig. 9 as an example). Leung et al. (2015) also stated that despite the installation of numerous parallel fibres inside the structure, it is challenging to maintain uniformity in the measurements. While the OFDR sensing method promises high accuracy and repeatability, actual measurements (such as strain and temperature changes) often exhibit nonsmooth curves due to environmental conditions and irregularities in sensor placement. ...
This study demonstrates the ability of the Rayleigh-based phase-noise compensated optical frequency-domain reflectometry (PNC-OFDR) sensing method to monitor the distributed temperature field with an ultra-short data acquisition period of 2 ms, a spatial resolution of 2 cm, and a temperature resolution of 0.1 °C. A heating cable (H-cable) was embedded within a cylindrical concrete mortar specimen and subjected to various heating powers. A sensing optical cable (temperature measurement cable) was placed adjacent to the H-cable to monitor the temperature distribution continuously. Two water-holding boxes were installed along the specimen at two positions to retain water. The study’s results indicated that the PNC-OFDR technique demonstrated a high sensitivity to even small temperature changes, enabling it to pinpoint water locations at two distinct points accurately. The research determined the minimal heating power required to successfully locate the water positions. The magnitude of the heating power exerted a significant impact on the temperature change. Three distinct phases of temperature increment were observed for a given heating period: rapid, fast, and gentle increase. The insights gained from this study have the potential to be applied in natural fields, allowing for the detection of groundwater and seepage phenomena in vulnerable slopes.
... Some of the advantages of optical fiber are resistance to electromagnetic field interference, small size and light weight, does not cause sparks against corrosion. Many researches on the use of optical fiber sensors as crack detection have been carried out, such as crack detection using Optical Time Domain Reflectometer (OTDR) techniques [8], Brillouin Optical Time Domain Reflectometer (BOTDR) [9,10] and Brillouin Optical Frequency Domain Analysis (BOFDA) [11,12]. Other studies by varying the angle of inclination of fiber optic embedded in concrete [13] and utilizing the bending loss in fiber optic [14,15,16]. ...
... Optical fiber sensors are a diverse group, broadly categorized into three types: point, multipoint, and distributed (Brogan & Walt, 2005;Hartog, 2017;Lee, 2003;Leung et al., 2015;Motil et al., 2016). Point sensors are limited to sensing at a single location on the optical fiber, typically where the fiber Bragg grating (FBG) is inscribed or at the optical fiber's end face. ...
... Distributed fiber optic sensor systems (DFOS) offer interesting possibilities for strain and temperature measurement, especially in concrete construction [1][2][3][4][5]. There are already isolated applications in the field of Structural Health Monitoring (SHM) of structural and civil engineering, geotechnics or in special heavy construction [6][7][8][9][10][11][12][13][14][15][16][17]. These measurement systems have enormous potential, particularly in terms of sustainable long-term use of structures, but also in terms of improving civil safety by monitoring the structural health [18,19]. ...
Distributed fiber optic strain measurement techniques have become increasingly important in recent years, especially in the field of structural health monitoring of reinforced concrete structures. Numerous publications show the various monitoring possibilities from bridges to special heavy structures. The present study is intended to demonstrate the possibilities, but also the challenges, of distributed fiber optic strain measurement in reinforced concrete structures. For this purpose, concrete beams for 3-point bending tests were equipped with optical fibers on the reinforcement and concrete surface as well as in the concrete matrix in order to record the strains in the compression and tension zone. In parallel, an analytical approach based on the maximum strains in the uncracked and cracked states was performed using the Eurocode 2 interpolation coefficient. In principle, the structural design correlates with the measured values, but the strains are underestimated, especially in the cracked zone. During load increase, structural distortions in the compression zone affected the strain signal, making reliable evaluation in this zone difficult. The information content of distributed fiber optic strain measurement in reinforced concrete structures can offer tremendous opportunities. Future research should consider all aspects of the bond, sensor selection and positioning. In addition, there is a lack of information on the long-term stability of the joint and the fiber coating, as well as the effects of dynamic loading.
