Journal of Korean Society of Steel Construction (한국강구조학회 논문집)

Korean Society of Steel Construction (한국강구조학회)
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Estimation of Dynamic Displacement and Characteristics of A Simple Beam from FBG Sensor Signals

FBG센서 응답을 이용한 단순보의 동적 변위 및 동특성 추정

  • Received : 2006.01.06
  • Accepted : 2006.07.27
  • Published : 2006.08.27
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Abstract

FBG sensors are capable of measuring the strain of structures easily and more durably than electric resistance gauges. Thus, many researches are dedicated to the application for the response monitoring or non-destructive evaluation of structures using FBG sensors. Additionally, the measured strains at the top and bottom of a cross-section can be transformed into the curvature of the section, which can be used to calculate its vertical displacement. Hence, this study aims to measure the dynamic strain signals of a steel section simply supported beam and to estimate the dynamic displacement from the strain signals, after which the estimated displacement is com pared with the measured displacement. The dynamic characteristics (natural frequency, damping ratio and mode shape) of the beam are predicted from both the estimated and measured displacement signals, and from the strain time history of the FBG sensors. The predicted properties are compared with those of an analytical model of the beam. The estimated displacement. However, the predicted dynamic properties from both the estimated displacements and the measured strains are well-correlated with those from the measured displacement. It is therefore appreciated that the estimation of the dynamic properties of FBG sensor signals is reasonable. Especially, the strain signal of the FBG sensor was amplified at a higher-frequency region in comparison with the displacement estimation with higher-mode properties.

FBG 센서는 기존의 전기저항식 게이지에 비해 구조물의 변형율 계측이 용이하고, 내구성이 우수하여 구조물의 응답 모니터링이나 비파괴손상평가 분야의 적용성에 대한 연구가 활발히 진행되고 있다. 또한, 구조물 단면의 상 로의 치환이 가능하며, 이 곡률을 이용하여 수직변위를 계산할 수 있다. 본 연구에서는, FBG 센서를 이용하여 I 형의 강재 단순보에서 충격에 의한 동적 변형율을 측정하고, 이를 이용하여 동적 변위를 추정하여 측정된 동적 변위와 비교 평가하였다. 또한, 추정된 변위와 측정된 변위 및 변형율 시간이력을 이용하여 단순보의 동특성( 고유진동수, 감쇠비 및 모드형상)을 추정하여 해석모델의 동특성과 비교하였다. 변형율을 이용한 변위의 추정은 측정 변위보다 최대 약 10% 정도 크게 나타났다. 그러나 추정된 변위 또는 변형율 이력을 사용하여 추정한 동특성은 측정된 변위를 사용하여 추정한 동특성과 거의 일치하였고, FBG 센서를 이용한 동특성 추정 결과는 양호한 것으로 나타났다. 특히, FBG 센서 변형율은 변위에 비해 고주파 특성이 증폭되기 때문에 고차모드의 동특성 추정에 유리하였다.

Keywords

References

  1. 정원석, 강동훈, 최은수, 김현민. (2005). '광섬유 격자센서를 이용한 철도 판형교의 증속 실험,' 한국강구조학회 논문집, 17권 6호
  2. Clough, R. W. and Penzien, J. (1993). Dynamics of Structural, the second edition, MaGraw-Hill
  3. Hayano, H. and Mita, A. (2005). Structural Health Monitoring System Using FBG Sensor for Simulating Detection of Acceleration and Strain, Smart Structures and Materials 2005: Sensors and Smart Structures Technologies for Civil Mechanical, and Aerospace Systems, edited by Masayochi Tomizuka, Proc. of SPIE Vol. 5765, pp. 624-633
  4. Meltz, G., Morey, W.W. and Glenn, W.H. (1989). Formation of Bragg gratings in optical fibers by a transverse holographic method, Optics Letters, Vol. 14, No. 15, pp. 823-825, 1989 https://doi.org/10.1364/OL.14.000823
  5. Hill, K.O., Malo, B. and Bilodeau, F., et al. (1993). Bragg gratings fabricated in monomode photosensitive optical fiber by UV exposure through a phase mask, Applied Physics Letters, Vol. 62, No. 10, pp. 1035-1037, 1993 https://doi.org/10.1063/1.108786
  6. Leng, J.S., Barnes, R.A., Hameed, A., Winter, D., Tetlow, J., Mays, G.C., and Fernando, G.F. (2005). Fibre Optic Sensor Protection System and its practical for structural integrity monitoring of concrete structures, Smart Structures and Materials 2005: Sensors and Smart Structures Technologies for Civil Mechanical, and Aerospace Systems, edited by Masayochi Tomizuka, Proc. of SPIE Vol. 5765, pp. 528-539
  7. Gandhi, M.V. and Thompson, B.S. (1992). Smart Materials and Structures, Chapman & Hall, London
  8. Stubbs, N., Park, S., Sikorsky, C., and Choi, S. (2000). A global nod-destructive damage assessment methodology for civil engineering structures, International Journal of System Science, Vol. 31, No. 11, pp. 1361-1373 https://doi.org/10.1080/00207720050197758