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SHM with Long-gage Fiber Optic Sensors

SHM with Long-gage Fiber Optic Sensors . Z.S. Wu, J. Zhang , Y.S. Tang, W. Hong, L. Huang Southeast University, Nanjing, China Ibaraki University, Hitachi, Japan. IBS Workshop, June 14, 2011 . Content. Background . Distributed sensing technique. 2. 1.

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SHM with Long-gage Fiber Optic Sensors

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  1. SHM with Long-gage Fiber Optic Sensors Z.S. Wu, J. Zhang, Y.S. Tang, W. Hong, L. Huang Southeast University, Nanjing, China Ibaraki University, Hitachi, Japan IBS Workshop, June 14, 2011

  2. Content Background Distributed sensing technique 2 1 Distributed long-gage FBG sensors Utilizing distributed strain measurement for SHM IBS Bridge 3 Sensor placement Global parameter identification Damage detection

  3. 1. Single Point Based Sensors

  4. Damaged! 1. Single Point Based Sensors • Strain Gauge No damage! OK?! Too Local! Huge Limitation!

  5. 2. Distributed long-gage FBG sensors

  6. 2. Distributed long-gage FBG sensors

  7. 2. Distributed long-gage FBG sensors Distributed sensing technique provides both the local information and the global information of the structure!

  8. 2. Distributed long-gage FBG sensors Distributed sensing does not means simple measurements! How to realize a nervous system of structures 1)Very dense distribution of using smart point sensors –useful ? 2)Continuous or partially continuous wiring of using line Macro strain sensors including long –gauge sensors – natural !

  9. 2. Packaged Long-gage FBG Sensors Design of Long-gage FBGsensor Wavelength variation (pm) Sε=1.2pm/με Strain variation (µε) Packaged with BFRP has no influence on strain sensitivity. Long-gage FBGsensor specimen Long-gage FBG sensor and its mechanical property

  10. 2. Distributed Strain Measurement for SHM (i) Global Information (a) Mode 1 Mode 3 Mode 2 (a) Acceleration (b) Strain

  11. (ii) Distribution of deformation from static strain distribution Conjugated beam method Distribution of deformation can be expressed by macro(long-gage) strain distribution in an explicit formula! Deformation at the first joint and mid-span of the pth element

  12. Best line of fit Data set at period t3 Feature = slope Interpretation No damage within sensor Si between t1 and t2 (iii) Damage Detection based on normalized modal macro-strain concept Data set at period t3 MMS of a target sensor, Si Best line of fit Data set at period t2 Set of data at period t1 MMS of a reference sensor, SR Increase in slope indicates damage within sensor Si between t2 and t3

  13. 3. Wayne Bridge: Sensor Layout Totally 44 sensors were installed on the 3rd and 6th girders.

  14. Fixing end Fiber sheath Fixing end Plastic tube FBG (a) Connector Connector Gage length Gage length Fixing end Fixing end Connector Connector (b) 3. Wayne Bridge: Sensor Layout

  15. 3. Wayne Bridge Test Results: Global Information Time history Time window 1 Time window 2 Time window 2

  16. 3. Wayne Bridge Test Results: Global Information 2.81 Hz Gird 3 Time history 2.81 Hz 2.82 Hz Gird 6 Acceleration (Drexel University) Measured Strain

  17. No damage if slope is stable 3. Wayne Bridge Test Results: Damage Detection Increase in slope indicates damage

  18. 3. Wayne Bridge Test Results: Global Information Fig. Magnitude relationship

  19. M X 3. Wayne Bridge Test Results: Neutral Axis Determination Neutral Axis Determination from dynamic strain measurement

  20. 3. Wayne Bridge Test Results: Neutral Axis Determination Static (Drexel Univ) Dynamic

  21. 4. Conclusion Distributed long-gage FBG sensors can be used for both global and local information monitoring Distributed strain measurement can be used for damage detection by utilizing developed damage index (like slopes, neural axis locations) 2 More interesting topics will be investigated by analyzing the measured distributed strains, e.g., comparing distributed strain time histories with traditional strain sensor outputs

  22. Thank you for your attention!

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