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

3. 1. Single Point Based Sensors

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

5. 2. Distributed long-gage FBG sensors

7. Distributed sensing technique provides both the local information and the global information of the structure!

8. 2. Distributed long-gage FBG sensors 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 ! Distributed sensing does not means simple measurements!

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

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

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

12. MMS of a reference sensor, S R MMS of a target sensor,Si Best line of fit Set of data at period t 1 Feature = slope Data set at period t 2 Data set at period t 3 Best line of fit Increase in slope indicates damage within sensor Si between t 2 and t 3 No damage within sensor Si between t 1 and t 2 Interpretation (iii) Damage Detection based on normalized modal macro-strain concept Data set at period t 3

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

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

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

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

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

18. Sensor VarianceSlope F10.99150.7305 F20.99610.8438 F30.99680.9821 F4 1 F50.99591.0111 F60.99571.0694 F70.99581.1408 F80.99431.1698 F90.99481.2117 F100.99521.2439 F110.99561.2757 F120.99311.3182 F130.99161.3117 F140.9851.2058 F150.98411.2119 F160.98291.2255 F170.98151.1661 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. More interesting topics will be investigated by analyzing the measured distributed strains, e.g., comparing distributed strain time histories with traditional strain sensor outputs 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 4. Conclusion

22. Thank you for your attention!