Damage detection via eigenfrequencies: numerical simulations and in situ experiments

Transcription

1 Damage detection via eigenfrequencies: numerical simulations and in situ experiments Karin HEDKVIST, Stéphane COMMEND - GeoMod Ing. SA Pierino LESTUZZI - IMAC-EPFL

2 Typical cut of a non-anchored retaining wall Concrete cracking and steel reinforcement corrosion (up to 30%) at the sole-facing connection

3 Loss of stiffness -> decrease 1st eigenfrequency K K = K/2 spring reinforcement M M hinge f 1 = SQRT(K/M)/2p f 1 = SQRT(K/2M)/2p Conclusion: f 1 < f 1 (here difference = 31%)

4 Soil-wall complex ->?

5 Outline 1. Presentation of the project 2. Numerical simulations 3. In situ mesurements 4. Conclusion

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9 1. Presentation of the project 2. Numerical simulations 3. Mesures in situ 4. Conclusion

10 P1 Lausanne Numerical analysis 1 (foundation on soft soil) P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 Terrain meuble Numerical analysis 2 (foundation on rock) Rocher Villeneuve P27 P28 P29 P30 P31 P32 P33 P34 P35 P36 P37 P38 P39 P40 P41 P42 P43 P44 P45 P46 P47 P48 P49 Rocher Terrain meuble Rocher Terrain meuble Panneaux mesurés Panneaux mesurés

11 DAMAGED NON-DAMAGED 1st numerical approach: linear concrete with CFS Q4, eigenmode E dyn = 50 GPa = 2E stat g = 24 kn/m 3 f1=21.0 Hz Difference: 37 % Explicit crack on 57% of surface: interface c0 f0 f1=13.2 Hz

12 NON-DAMAGED 2nd numerical approach: time history under blow at top A Blow ux(t) at A 1kN Δt =0.01s ax(t) at A Fourrier transform f=20.9 Hz vs. Nondamaged eigenfreq. 1: f=21.0hz

13 DAMAGED 2nd numerical approach: time history under blow at top A Blow ux(t) at A 1kN Δt =0.01s ax(t) at A Fourrier transform f=16.3hz vs. damaged eigenfreq. 1: f=13.3 Hz

14 Viscous dampers Viscous dampers 3rd numerical approach: time history under blow at top, with soil u x and u y =0

15 3rd numerical approach: time history under blow at top, with soil Fill Interfaces Moraine Fill Glacier deposits Moraine

16 DAMAGED NON-DAMAGED 3rd numerical approach: time history under blow at top, with soil f1=19.8hz.avi f1=17.8hz

17 Parametrical study Load shape Mesh size f1=19.80 Hz f1=19.80 Hz Sinus (18Hz) : f1=19.64 Hz diff. Non-damaged and damaged << f1=19.80 Hz Mesh size / 2 : f1=18.40 Hz Mesh size x 2 : f1 > 40 Hz!! Number of blows 1 blow: f1=19.80 Hz 2 blows: f1=19.80 Hz + noise at 40 Hz Domain size and shape f1=19.80 Hz h/2 and bx2: f1= Hz hx2 and bx1: f1= Hz hx2 and bx2: f1= Hz + noise at 40 Hz h/2 and b/2: f1= Hz + noise at 40 Hz

18 Wall + soil Time history Time history Wall alone Eigenmode Wall P10 (foundation on soft soil) P41 (foundation on rock) Freq. (Hz) Diff. Freq. (Hz) Diff. 27% 19% Nondamaged Damaged % Nondamaged Damaged % Nondamaged Damaged % %

19 Conclusion on numerical studies Recall: elastic wall with CFS elements damage introduced as explicit c0 f0 interface f1(damaged) < f1(non-damaged): OK! On wall alone: difference = 20 to 30% On wall + soil: difference = 10 to 15%... Is it enough?? Could be done, if needed: same on nonlinear beam with variable steel reinforcement

20 1. Presentation of the project 2. Numerical simulations 3. In situ mesurements 4. Conclusion

21 Measurements types Measurements Ambiante vibrations Forced vibrations (blow with excavator shovel) Measurements before excavation behind wall: April 6th 2016: April 29th 2016: M10 M14, M41 M45 M7 M10, M15 M19 and M24 M28

22 Measurements types

23 Example: forced vibrations

24 Measurement analysis (soft soil) ambiant forced Different signature => Different wall state??

25 Measurement analysis (rock) ambiant forced

26 Conclusions Good correlation for order of magnitude of f1 between numerical simulation and measurements: 15 to 20 Hz Difficulty to isolate f1 from other frequencies (both numerical & on site) In fall-winter 2016: excavation behind wall Measurement of natural frequency of wall «alone» Possibility to know actual state of sole-facing connection Correlation between measured f1 and wall condition??? Thank you: Thomas Zimmerman for the idea and the discussions OFROU (pilot study financing) GUMA team (coordination with AR49 works + discussions)