• Smart Structures and Systems
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• v.1 no.4
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• pp.355-368
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• 2005

Large and complex structures are being built now-a-days and, they are required to be functional even under extreme loading and environmental conditions. In order to meet the safety and maintenance demands, there is a need to build sensors integrated structural system, which can sense and provide necessary information about the structural response to complex loading and environment. Sophisticated tools have been developed for the design and construction of civil engineering structures. However, very little has been accomplished in the area of monitoring and rehabilitation. The employment of appropriate sensor is therefore crucial, and efforts must be directed towards non-destructive testing techniques that remain functional throughout the life of the structure. Fiber optic sensors are emerging as a superior non-destructive tool for evaluating the health of civil engineering structures. Flexibility, small in size and corrosion resistance of optical fibers allow them to be directly embedded in concrete structures. The inherent advantages of fiber optic sensors over conventional sensors include high resolution, ability to work in difficult environment, immunity from electromagnetic interference, large band width of signal, low noise and high sensitivity. This paper brings out the potential and current status of technology of fiber optic sensors for civil engineering applications. The importance of employing fiber optic sensors for health monitoring of civil engineering structures has been highlighted. Details of laboratory studies carried out on fiber optic strain sensors to assess their suitability for civil engineering applications are also covered.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.10a
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• pp.617-619
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• 2022

An embedded fiber-optic sensor was manufactured using 3D printing technology for distributed structural monitoring. Strain distribution of the embedded sensor was measured by the optical frequency domain reflectometry, and real-time data visualization for the embedded sensor model was demonstrated.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.2
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• pp.44-50
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• 2012

When the fiber Bragg gratings are embedded in a fiber-optic Sagnac loop for measuring temperature or strain, it is difficult to separate the Bragg wavelengths. The transmitted light is mixed with the reflected Bragg wavelengths in the photo-detector, working as noises. To suppress the noises, we placed the FBG sensors and a fiber-optic attenuator at asymmetric positions in the loop. With the arrangement the reflected light became much bigger than the transmitted light, enabling the separation of the reflected Bragg wavelengths with almost the same signal-to-noise ratio of the FBG sensors outside the loop.

• Composites Research
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• v.25 no.6
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• pp.211-216
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• 2012

FBG sensor peaks could be split due to polarization by shear strain, when the fiber optic sensors embedded or attached to the structure. For the fiber optic sensor packages, sensor grating has to be protected from shear strains. Also, pretension has to be applied to the sensor because compressive strain must be measured. Without pretension of sensor, the sensor does not show any change of signal until it is stretched. In order to mesure compressive and tensile strains, two fixing point and prestressed sensor need. In the fixing point, just holding the optical fiber cause slip between core and cladding in the fiber. A Fixation method of prestressed FBG sensors fixed with partially stripped fibers was developed. The sensor package has the prestress controllable fixtures at the fixing points. Prestress to the sensor imposed by controlling the two fixed points with bolts and nuts make it easy to measure compressive strain as well as tensile strain. The fiber optic sensor packages applied to the actual structure and the structural monitoring system using the package can be applied to safety through surveillance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.223-236
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• 1999

The need to monitor and undertake remidial works on large structures has greatly increased in recent years due to the appearance of widespread faults in large structures such as bridges and buildings, etc, of 20 or more years of age. The health condition of structures must be monitored continuously to maintenance the structures. In order to do in-situ monitoring, the sensor is necessary to be embedded in the structures. Fiber optic sensors can be embedded in the structures to get the health information in the structures. The fiber sensor was constructed with $3{\times}3$ fiber couplers to sense the multi-point strains and failure instants. The 4 RC (reinforced concrete) beams were made to 2 of A type, 2 of B type beams. These beams were reinforced by the reinforcing bars, and were tested under the flexural loading. The behavior of the beams was simultaneously measured by the fiber optic sensors, electrical strain gages, and LVDT. The states of the beams were interpreted by these all signals. By these experiments, There were verified that the fiber optic sensors could measure the structural strains and failure instants of the RC beams, The fiber sensors were well operated until the failure of the beams. It was shown that the strains of the reinforcing steel bar can be used to monitor the health condition of the beams through the flexural test of RC beams. On the other words, the results were arrived that the two strains in the reinforcing bar measured at the same point can give the information of the structural health status. Also, the failure instants of beams were well detected from the fiber optic filtered signals.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.124-133
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• 2007

In our research, we focused on the FBG sensor system which is one of the fiber optic sensor system. The FBG sensor system is used for structural measurements. The problem of FBG sensor is very thin and weak. The methods that can protect FBG optical fiber sensor front outside forces such as the impacts are investigated. The FBG sensor embedded in the fiber reinforced composites which can replace the reinforcing steel bars in concretes can be applied to the concrete structures by embedding to the composite materials. The progresses in tensile strength of FBG sensor embedded in the reinforcing FRP bars in the concrete structures compare to plain FBGs were observed and the good long term durability is expected.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.27-30
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• 2002

PMFBG sensor was fabricated using phase mask and Excimer laser. The reflected wavelength of PMFBG sensor had dual peaks due to intrinsic birefringence. To discover the polarization axes, peak sensitivity was measured under compression test. The signal characteristics of PMFBG sensor were also examined in embedding condition. The embedded PMFBG sensor in epoxy block was loaded for the transverse strain measurements. Experiments showed that the PMFBG sensor could successfully measure the transverse strain. This PMFBG sensor is useful for the structures that require measuring transverse stram.

• Journal of Sensor Science and Technology
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• v.8 no.3
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• pp.232-238
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• 1999

Single mode fiber optic interferometers using the Fabry-Perot configuration were embedded in a reinforced concrete structure. These interferometers investigated the character of phase shift and strain for internal loads. The 10 mm length of FFPI in the continuous length of single mode fiber (SMF) were produced with two pieces of SMF coated were $TiO_2$ dielectric film utilizing the fusion splicing technique. The fabricated fiber optic Fabry-Perot interferometer(FFPI) and the 6 mm length of steel bar were buried with specimen ($100{\times}100{\times}50\;mm^3$) which was made of concrete structure. The resin protects FFPI and fiber leads from squeezed concrete. Sensors at different point in the structure were multiplexed by TDM (Time Division Multiplexing) method and the deformation to the external loads at each point could be monitored simultaneously. The output signals were proportional to the external loads applied to the structure and the sensitivity of the sensors were $1.03^{\circ}/kg$ and $0.76^{\circ}/kg$ respectively.

• Journal of the Korean Geotechnical Society
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• v.16 no.4
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• pp.201-208
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• 2000

Axial load distribution in model piles was measured by fiber Bragg Grating(FBG) sensor to investigate a possibility of analyzing the load transfer mechanism by Fiber Optic sensor system. Since FBGs of different wave lengths can be multiplexed in an optical fiber, the installation of sensor system and the measurement of strains are relatively simple, compared with consisting strain gages. In this study, FBG sensors and electric strain gages were embedded in the same piles and the distributions of load transfer by two sensor systems were measured. It was observed from the test results that the variations of axial load by both systems showed insignificant difference and that the measurements by FBG were smoother than those by strain gage. Under the environments of laboratory testing, survival rate of embedded FBG system was higher than that of strain gage. Therefore, it was concluded that the use of FBG sensor has a great potential for the measurement of load transfer for pile foundation.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.717-723
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• 2002

Recently, the interest in safety assessment of civil infrastructures is increasing in Korea. Especially, as bridge structures become large-scale, it is necessary to monitor and maintain the safety state of bridges, which requires the monitoring system that can make a long-term measurement during the service time of bridge. In this paper, advanced fiber optic sensors for long-term measurement, setup techniques of bridge monitoring system and the assessment of measured data are introduced. Attached or embedded optical fiber sensors to structural members of small and big structures including Sung San Bridge are surveyed. For the Sung San Bridge, the responses of the fiber optic sensors by 30 ton weigh truck loads with various speeds ate measured. Monitoring system is also applied to the mock-up of bridges. The monitoring capability of the advanced fiber optic sensor system was confirmed.