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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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... overcome the above shortcomings, the extrinsic Fabry-Perot Interferometer (EFPI) can be employed [31,32,71]. The EFPI is constituted by a capillary tube containing two cleaved optical fibers facing each other ( Fig. 1), but leaving an air gap of a few microns or tens of microns between them. When light is launched into one of the fibers, a back-reflected interference signal is obtained from the reflections of the incoming light on the glass-to-air and air-to-glass interfaces, respectively. This interference can be demodulated using coherent or ...
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... on a steel reinforcing bars to be embedded inside the structure [72]. The sensing bar consisted of a FBG strain sensor and a thermocouple for temperature compensation. A narrow groove was notched on the bar and the FBG sensor was attached into the groove with adhesive at the middle of the bar while the thermocouple was bonded on the opposite side (Fig. 10). The test results showed that the strain measured by the sensing bars agreed with the results from the mechanical deformeter ...
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... approach to package FBG strain and temperature sensors is to embed the sensors into fiber reinforced polymer (FRP) (Fig. 11). The strain sensors can measure both tensile and compressive strain with high signal-to-noise ratio. Strain up to 5,000 microstrains with 1-2 microstrains resolution can be measured [77]. This packaging method has been validated extensively in Shangdong Binzhou Yellow River Highway Bridge in Mainland China, which was open for traffic ...
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... degradation occurs in cable stayed or suspension bridges, the load distribution among the cables will be changed. By continuously monitoring the tensile stresses at the cables induced by traffic load and temperature variation, any abnormal variation may indicate damage and fatigue of the bridge structure. The point sensor in Fig. 11 is not appropriate for installation on the cable. A smart cable was therefore developed to measure the load carried by the cable (Fig. 12). The optical fiber and the glass fibers were dragged by tension in parallel (Fig. 13) [44]. Resin was applied and then the composite solidified through heating in a furnace. The resulting FRP-FBGs ...
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... continuously monitoring the tensile stresses at the cables induced by traffic load and temperature variation, any abnormal variation may indicate damage and fatigue of the bridge structure. The point sensor in Fig. 11 is not appropriate for installation on the cable. A smart cable was therefore developed to measure the load carried by the cable (Fig. 12). The optical fiber and the glass fibers were dragged by tension in parallel (Fig. 13) [44]. Resin was applied and then the composite solidified through heating in a furnace. The resulting FRP-FBGs consisted of an optical fiber at the center of the cross section and the FBG sensors were located at the prespecified positions. The strain ...
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... temperature variation, any abnormal variation may indicate damage and fatigue of the bridge structure. The point sensor in Fig. 11 is not appropriate for installation on the cable. A smart cable was therefore developed to measure the load carried by the cable (Fig. 12). The optical fiber and the glass fibers were dragged by tension in parallel (Fig. 13) [44]. Resin was applied and then the composite solidified through heating in a furnace. The resulting FRP-FBGs consisted of an optical fiber at the center of the cross section and the FBG sensors were located at the prespecified positions. The strain of the FBG sensors would be the same as the surrounding glass fibers. To find the ...
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... consisted of an optical fiber at the center of the cross section and the FBG sensors were located at the prespecified positions. The strain of the FBG sensors would be the same as the surrounding glass fibers. To find the actual mechanical strain, additional temperature sensors should be employed (either by using FBG temperature sensors in Fig. 11b or thermocouple). In the smart cable, the FRP-FBG cable replaces the central wire of a typical 7-wire steel cable (Fig. 12). Since the stiffness of FRP is much lower than steel, the load capacity of the smart cable is assumed to be six in seven of the original steel ...
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... positions. The strain of the FBG sensors would be the same as the surrounding glass fibers. To find the actual mechanical strain, additional temperature sensors should be employed (either by using FBG temperature sensors in Fig. 11b or thermocouple). In the smart cable, the FRP-FBG cable replaces the central wire of a typical 7-wire steel cable (Fig. 12). Since the stiffness of FRP is much lower than steel, the load capacity of the smart cable is assumed to be six in seven of the original steel ...
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... design, temperature sensors were placed alongside the mechanical strain sensor. A special packaging technique for FBG strain sensor with self temperature compensation by using two FBG sensors has also been developed [74]. Two FBG sensors were connected in series (about 30 mm separation) and sandwiched between two plastic (polypropylene) slabs (Fig. 14). The mechanical strain sensitive FBG sensor was fixed by cyanoacrylate adhesive. The other sensor was isolated from mechanical strain by a special packaging scheme. The grating was slightly bent and enclosed in a thin metal tube in order to protect the grating and prevent the transfer of mechanical strain to the grating. The packaged ...
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... consequence on safety and serviceability. The immediate loss due to elastic deformation can be estimated precisely. However, it is difficult to predict the time dependent loss from several intertwined factors such as concrete creep, steel relaxation, concrete shrinkage and thermal effects. A smart steel strand similar to the 7-wire smart cable in Fig. 12 was developed with a single mode optical fiber to monitor the prestressing force during operation [38,62,104]. The central steel wire is replaced by a FRP cable with single mode silica optical fiber at the center of the rod (Fig. 13). The strain distribution along the smart steel strand was monitored by using Brillouin optical time ...
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... steel relaxation, concrete shrinkage and thermal effects. A smart steel strand similar to the 7-wire smart cable in Fig. 12 was developed with a single mode optical fiber to monitor the prestressing force during operation [38,62,104]. The central steel wire is replaced by a FRP cable with single mode silica optical fiber at the center of the rod (Fig. 13). The strain distribution along the smart steel strand was monitored by using Brillouin optical time domain analysis (BOTDA). Unlike Brillouin optical time domain reflectometry, the sensor has to form a closed loop for measurement. Since the strain is averaged within the spatial resolution and the duration of data acquisition is several ...
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... spatial resolution of commercial BOTDR/A model is about 1 m. The high strain gradient near stress concentration region is averaged and may not be identified from the BFS in time domain. An innovative and simple method to identify any local damage is shown in Fig. 15. Two optical fibers with different lengths L 1 and L 2 are connected to an optical switch. When L 1 À L 2 j jis less than the spatial resolution, it can improve the density of measurement points with fixed spatial resolution. If there is local stress concentration, a significant deviation is shown near the stress concentration region ...
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... concentration, a significant deviation is shown near the stress concentration region in the plot of the difference between the two strain measurements. Strain induced by temperature change can be compensated by two optical fibers embedded in the same matrix. With one of them sensitive to both mechanical and thermal strain (B1) while the other Fig. 14 Schematic diagram of a FBG strain sensor with self temperature compensation sensitive only to thermal strain (B2), the mechanical induced strain can be deduced from Eq. 5 with a single calibration coefficient (K e ) ...
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... respectively. The sensing capability can be enhanced by incorporating FBG strain sensors to provide precise strain measurement at critical positions such as the anchorage points and perform dynamic strain measurement with sampling rate in range of kilo-hertz. In practical measurement, the FBG interrogator and BOTDA can be coupled as shown in Fig. 16. From the tests in [104], when the Bragg wavelength does not overlap with the wavelength of the laser of the distributed sensor, there is no noticeable interaction between FBG sensors and BOTDA. By incorporating FBG sensors with BOTDA measurement, the mechanical and temperature induced strain can be decoupled [38]. Assume there is no ...
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... employed in such a large scale to monitor bridge integrity [24]. By using OTDR, several intensity based sensors can be multiplexed in time domain. A multi-gauge crack sensor based on the intensity of Fresnel reflection was developed [29,30]. An optical fiber was sliced into several segments by precision cleaver, each representing a gauge length (Fig. 17). The cleaved segments were spliced along one line to form the quasi-distributed sensor. By using OTDR, the intensity of the Fresnel reflection at each splicing point was measured. The sensor showed linear relation between the integral crack width and return loss of the corresponding segment. The sensor can be embedded into reinforced ...
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... was developed [7,63,96] to monitor multiple cracks by a single optical fiber. With known crack opening direction, the optical fiber is aligned at an angle to the crack. To facilitate the installation, the optical fiber with predefined orientation is first embedded into a 2 mm thick polyester plate filled with sand to make the plate more brittle (Fig. 18). The sensor plate is attached onto concrete surface by epoxy. To embed the plate into concrete, coarse aggregates, which provide interlocking with concrete, are inserted before hardening of polyester plate. When crack in concrete opens, the sensor plate is cracked and the optical fiber has to bend in order to maintain continuity. Bend ...
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... interlocking with concrete, are inserted before hardening of polyester plate. When crack in concrete opens, the sensor plate is cracked and the optical fiber has to bend in order to maintain continuity. Bend loss (and hence a drop in the intensity of the Rayleigh backscattered signal) is hence induced near the crack location (the lower graph of Fig. 18). The OTDR is used to measure the intensity of Rayleigh backscattered signal with respect to time. The slight decrease in backscattered signal is due to attenuation, while sudden signal loss corresponds to the opening of a crack. The amplitude of the signal loss is related to the crack opening size, optical fiber type and the angle ...
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... spatial resolution of Rayleigh scattering can be enhanced in a cost effective manner by using optical frequency domain reflectometry (OFDR) instead of optical time domain reflectometry (OTDR). Optical fibers were bonded on the lateral surface of a reinforced concrete beam as shown in Fig. 19. The spatial resolution is 6 mm. From Fig. 19, the local stress concentration at tension side as well as compressive strain can be ...
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... spatial resolution is 6 mm. From Fig. 19, the local stress concentration at tension side as well as compressive strain can be measured. ...
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... corrosion sensor for reinforced concrete structures was developed based on the variation of Fresnel [99]. The sensor is made by sputtering a very thin pure iron coating (about 200 nm) on the cleaved end of a single mode telecommunication optical fiber (Fig. 21). The iron coating reflects the light as a mirror. When the surrounding environment becomes corrosive (either by chloride ion or carbonation), the coating is depleted and the reflectivity is significantly reduced. The sensor reflectivity can be measured by OTDR. To monitor the reflectivity of multiple sensors, an optical splitter can be ...
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... the vertical load from the steel truss girders to the concrete-in-steel columns. In order to monitor the stress of the key components during the construction and operation phases, 70 FBG strain sensors were installed on the steel truss girders, steel beams, concrete-in-steel columns and the giant columns. 16 FRP-FBG smart cables as shown in Fig. 12 were installed to monitor the tensile stress carried by the steel cables. In addition, 35 FBG temperature sensors were installed for temperature compensation of the strain sensors. The National Aquatic Center is a complex structural steel-membrane structures. Due to high redundancy of the steel structure, thermal induced stress may be ...
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... array was then used for long-term monitoring of the anchor bonding. To make a similar smart ground anchor, several FBG strain sensors were embedded along a 7-wire steel strand [59]. FBG sensors were embedded in the central wire, while the other six wires were wrapped helically around the central one. The concept is similar to the smart cable in Fig. 12. The only difference was that the central wire consisted of a steel tube instead of FRP. The outer and inner diameters of the tube were 5.24 and 2 mm, respectively. The FBG sensors were embedded inside the steel tube and grouted by liquid epoxy ...
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... life of 30 years along the crown of the tunnel, which is expected to be the hottest location as fire causes hot air to rise up. The installation took 4 days between 1 a.m. and 4 a.m. in the morning by a 4-man team with a hydraulic elevation truck. The installed system was subjected to a fire test with ignition of a 50 cm diameter basin of diesel (Fig. 31). The point of fire could be clearly located in 80 s ...
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... field application example of BOTDA was the installation of an 1 km long telecommunication silica single mode optical fiber (embedded in FRP as in Fig. 13) in Daqing Oilfield to monitor the strain variation during the grouting of the downhole and perforation [105]. The FRP cable with sensing optical fiber was clamped on the surface of the pipe by stainless steel hoops and the whole pipe was covered by cement mortar to ensure deformation compatibility between the pipe and optical fiber. ...
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.
