• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.3
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• pp.241-247
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• 2015

Deflection and deformation occur easily in structures with long length, such as bridges and pipelines. Shape monitoring is required for ensuring their structural health. A fiber Bragg grating (FBG) sensor can be used for monitoring a large-scale structure because of its advantage of multiplexing. In this study, FBG sensors were used for monitoring a composite beam structure, and its strains were measured at multiple points. Thereafter, a shape estimation technique based on the strains was studied. Particularly, a three-dimensional shape estimation technique was proposed for accurate structural health monitoring. A simple experiment was conducted to verify the performance of the shape estimation technique. The result revealed that the estimated shape of the composite beam structure was in agreement with the actual shape obtained after the deformation of the specimen. Additionally, the deflection at a specific point was verified by comparing the estimated and actual deformations measured using a micrometer.

• Composites Research
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• v.17 no.2
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• pp.28-33
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• 2004

Failure detection in a cross-ply laminated composite beam under tensile loading were performed using a fiber Bragg grating (FBG) sensor. A Passive Mach-Zehnder interferometric demodulator was proposed to enhance sensitivity and bandwidth. The proposed FBG sensor system without active device such as a phase modulator is very simple in configuration, easy to implement and enables the measurement of high-frequency vibration with low strain amplitude such as impact or failure signal. Failure signals detected by a FBG sensor had offset value corresponding to the strain shift with vibration at a maximum frequency of several hundreds of kilohertz. at the instant of transverse crack propagation in the 90 degree layer of composite beam.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.5
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• pp.343-349
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• 2005

In this research, the fiber Bragg grating sensors with long gauge for displacement measurement in the long distance is developed and tested. The sensors show an accuracy and a capability for displacement measurement oin long distance. Monitoring using static logger of system of FBG sensor with strained optical fiber shows the capability of measurement in the harsh environment such as strong wind. Measurement of long distance displacement by optical fiber sensor if use $250{\mu}m$ optical fiber and impose some strong pre-tension shows possibility in monitoring of nuclear containment structure.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1057-1060
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• 2008

For high performance concrete, due to its low water cement ratio (water binder ratio) and addition of mineral admixtures, pretty high autogenous shrinkage and thermal deformation occur at very early age of casting (especially before hardening). This may lead to early age cracking of HPC structures, and then may influence the durability of HPC. This paper has monitored the early age properties of HPC successfully by embedded FBG strain sensor. The results showed that the deformation increased rapidly within the first day after HPC casting. And its value is up to $85{\mu}{\varepsilon}$, which is the 30% of two-month deformation ($280{\mu}{\varepsilon}$). Considering the durability and permeability of HPC, the first-day deformation is pretty high and can not be neglected. Also the superior capability of FBG sensors such as continuity, stability and multiplexed technique etc, has been demonstrated.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.199-202
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• 2011

플로팅구조물은 열악한 해양환경상태에 있기 때문에 구조물응답에 대한 실시간 모니터링 기술을 적용하여 구조안전성을 확보해야 한다. 특히 기존의 전기 저항식 스트레인 게이지 단점을 극복한 광섬유 센서를 이용하여 실시간 모니터링 시스템 개발에 관한 연구가 필요하다. 본 논문에서는 플로팅구조물의 축소 모델에 광섬유 센서 중 하나인 FBG센서를 부착하고 실험용 수조에 설치하여 광학 스펙트럼 분석기를 통해 중심파장을 측정한 후 변형률을 계산하였다. 또한 유한요소 모델을 유한요소 해석 프로그램인 ABAQUS를 사용하여 모델링하고 유한요소 해석을 통해 변형률을 출력하고 실험결과와 해석 결과를 비교하여 광섬유 센서를 이용한 플로팅구조물의 실시간 모니터링을 위한 기초자료를 제공하고자 한다.

• Journal of the Korean Geotechnical Society
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• v.27 no.6
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• pp.17-26
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• 2011

Ground anchor method is one of the most popular reinforcing technology in Korea. For the sound monitoring of slope reinforced by permanent anchor for a long period, monitoring the tension force of ground anchor is very important. However, special technology except conventional load cell has not been developed for this purpose. In this paper, a new method is described to replace the conventional strain gauge and V.W. type load cell which has been commonly used as a prestress force monitoring tool for a short-term and long-term. Four 11.5 m long strain detectable tension type anchors were made using FBG sensor embedded tendon since FBG sensor is smaller than strain gauge type load cell and does not have noise from electromagnetic wave. Each two set strain detectable tension type anchors were installed into the different ground conditions, i.e., soft rock and weathered granite soil. Prestress force of ground anchor was monitored during the loading-unloading step from in-situ pullout test using proposed FBG sensor embedded in the tendon and the conventional load cell Test results show that the prestress force monitored from FBG sensor may well be used practically, for it almost matches with that measured from expensive load cell.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.2
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• pp.47-55
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• 2004

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.397-406
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• 2003

Several sensor systems are used to estimate the reinforcing effect of stabilizing pile in slopes, and to find a failure surface in slopes effectively. FBG(Fiber Brags Crating) sensor, V/W(Vibrating Wire) sensor and inclinometer have shown a great potentiality to serve real time health monitoring of the reinforcing structures. Field tests and test results have shown great solutions for sensor systems of Smart Structures. The purpose of this research is to seek for the relationships among the slope movement and the reinforcing effect of stabilizing pile, and the strain distribution of stabilizing pile in a active zone by analyzing the data from the in-situ measurement so that the possible failure surface should be well defined based on the relationships. The field test results have shown that the data by FBG sensor are well coincided with those of V/W sensor and inclinometer, and the reinforcing effect of the stabilizing pile is good enough.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.5
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• pp.513-516
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• 2011

The dynamic behavior of a small wind-turbine blade was analyzed experimentally. Arrays of fiber Bragg-Grating (FBG) sensors attached along the blade were used to measure the strains of the blade surface. An impact test was performed to estimate the resonance frequencies of the fundamental and higher modes of the cantilever blade system developed for this study. The results were similar to the results for conventional strain gages. However, FBG sensors could sense modes that strain gauges could not sense. The strains obtained from the FBG sensor array were used to estimate displacement-mode shapes of the blade.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.1
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• pp.6-12
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• 2010

Fiber optic sensor using fiber Bragg grating(FBG) probes is used for monitoring strain and temperature distributed on the wide surfaces of large structures. In this paper, in order to use many FBG probes in one optical fiber line, we propose a complex multiplexing technology which is composed of two techniques, one is time division multiplexing and another is wavelength division multiplexing. However, we only investigate the characteristics of time division multiplexing because FBG sensors basically can be operated by wavelength division multiplexing. We calculate the optimal reflectivities and the lengthwise location of five FBG probes in serial connection in order to obtain the unique reflected intensities from the FBG probes. We fabricate five FBG probes with the reflectivities of 13%, 16%, 25%, 40% and 80%, which are determined by the theoretical calculation, and observe the signal reflected from each FBG in the time domain from the experiment. There are differences between experimental and theoretical results caused by the signal noise and the differences of reflectivities of FBG probes. But the experimental results shows the reflected signals of five FBG probes which prove the availability of complex multiplexing.