2004년도 대한토목학회 학술발표회

임현우 , 한국과학기술원 건설및환경공학과 석사과정문영종 , 한국과학기술원 건설및환경공학과 박사과정이종헌 , 경일대학교 토목환경공학과 교수이인원 , 한국과학기술원 건설 및 환경공학과 교수

Experimental Comparison of Structural Experimental Comparison of Structural

Damage Detection Methods Damage Detection Methods

22Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea

Introduction

• Damage detection becomes a very important issue and, there are a lot of evaluation methods in this field.

• Experimental investigation was planed for comparison of some of these various methods.

• Aluminum cantilever beams are used for comparison of time, frequency domain and mode shape method.

• Experiment is focused on the applicability of the three methods

in practical situations.

33Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea

• Equipment

- FFT analyzer ( B&K )

- impact hammer ( PCB )

- accelerometer ( B&K )

- shaker ( YAVETEX )

• Equipment

- FFT analyzer ( B&K )

- impact hammer ( PCB )

- accelerometer ( B&K )

- shaker ( YAVETEX )

60cm aluminum beam4cm

0.4cm4

1

4

2

4

3• Damage case

- size (%) : 5, 10, 20, 30

- location : 1/4, 2/4, 3/4

Experimental setup

44Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea

Frequency domain method

0

0.1

0.2

0.3

0.4

0.5

1/4 2/4 3/4

(%)

Diff

ere

nces

10% Damage20%30%

Damage location

0

0.2

0.4

0.6

0.8

1/4 2/4 3/4

(%)

Diff

ere

nces

10% Damage20%30%

Damage location

0

0.2

0.4

0.6

0.8

1/4 2/4 3/4

(%)

Diff

ere

nces

10% Damage20%30%

Damage location

• Comparison of natural freq.

- measured freq : 1st,2nd,3rd

- damage case : 10, 20, 30%

: 1/4, 2/4, 3/4

• Comparison of natural freq.

- measured freq : 1st,2nd,3rd

- damage case : 10, 20, 30%

: 1/4, 2/4, 3/4 Differences in 1st natural freq.

Differences in 3rd natural freq.Differences in 2nd natural freq.

55Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea

• FRF based method• FRF based method

-

where,

: undamaged FRF

: damaged FRF

j

dij

uijiFRF )()(

)( uij

)( dij

FRF Based Method

- 3

- 2

- 1

0

1

2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Damage Location

FR

F_C

Diff

eren

ces

FRF Based Method

- 3

- 2

- 1

0

1

2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Damage Location

FR

F_C

Diff

eren

ces

FRF Based Method

- 3

- 2

- 1

0

1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Damage Location

FR

F_C

Diff

eren

ces

Damage size 30%, location 1/4

Damage size 30%, location 2/4 Damage size 30%, location 3/4

66Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea

Mode shape method Damage location 1/4

-1200

-800

-400

0

400

800

1200

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Measured point

Am

plit

ud

e

Undamaged

20% Damage30% Damage

Damage location 2/4

-1200

-800

-400

0

400

800

1200

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Measured point

Am

plit

ud

e

Undamaged20% Damage30% Damage

Damage location 3/4

-1200

-800

-400

0

400

800

1200

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Measured point

Am

plit

ud

e

Undamaged20% Damage30% Damage

• Comparison of mode shape

- measured mode shape : 2nd

- damage case : 10, 20, 30%

: 1/4, 2/4, 3/4

• Comparison of mode shape

- measured mode shape : 2nd

- damage case : 10, 20, 30%

: 1/4, 2/4, 3/4 Damage location 1/4

Damage location 2/4 Damage location 3/4

77Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea

• Wavelet transform• Wavelet transform

• Simulation ( FEM )

- dimension (cm) : 60×4×0.4

- no. of element : 240

- element type : beam

• Simulation ( FEM )

- dimension (cm) : 60×4×0.4

- no. of element : 240

- element type : beam

10 20 30 40 50 60 70 80 90 100 110 120

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

x 10-4

Finite element model by MIDAS

Damage size 30%, location 2/4

• Damage

- size (%) : 10, 20, 30

- location : 1/4, 2/4, 3/4

- element no. : 60, 120, 180

88Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea

• Mode Shape (MS)

where, : Undamaged mode shape vector

: Damaged mode shape vector

• Mode Shape Slope (MSS)

• Mode Shape Curvature (MSC) & (MSCS)

,

j

dij

uijiMS

j

dij

uijiMSS 22 )'()'(

uijdij

j

dij

uijiMSC ""

j

dij

uijiMSCS 22 )"()"(

99Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea

Mode Shape (MS)

-0.0016

-0.0012

-0.0008

-0.0004

0

0.0004

1 11 21 31 41 51 61 71 81 91 101 111 121

Element No.

MS v

alu

e

Mode Shape Slope (MSS)

0

0.000001

0.000002

0.000003

0.000004

0.000005

1 11 21 31 41 51 61 71 81 91 101 111

Element No.

MS

S v

alu

e

Mode Shape Curvature (MSC)

- 0.00002

0

0.00002

0.00004

0.00006

0.00008

0.0001

1 12 23 34 45 56 67 78 89 100 111

Element No.

MS

C v

alu

e

Mode Shape Curvature Square (MSCS)

- 0.00000012

- 0.00000008

- 0.00000004

0

0.00000004

1 13 25 37 49 61 73 85 97 109 121Element No.

MS

CS

valu

e

• Simulation : damage case 20%, 1/4

1010Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea

Time domain method

Time(acc) - InputWorking : Input : Input : FFT Analyzer

9.6m 10m 10.4m 10.8m 11.2m 11.6m 12m 12.4m

-60

-40

-20

0

20

40

60

[s]

[m/s 2] Time(acc) - InputWorking : Input : Input : FFT Analyzer

9.6m 10m 10.4m 10.8m 11.2m 11.6m 12m 12.4m

-60

-40

-20

0

20

40

60

[s]

[m/s 2]Time(acc) - InputWorking : Input : Input : FFT Analyzer

9.6m 10m 10.4m 10.8m 11.2m 11.6m 12m 12.4m

-60

-40

-20

0

20

40

60

[s]

[m/s 2] Time(acc) - InputWorking : Input : Input : FFT Analyzer

9.6m 10m 10.4m 10.8m 11.2m 11.6m 12m 12.4m

-60

-40

-20

0

20

40

60

[s]

[m/s 2]

Time(acc) - InputWorking : Input : Input : FFT Analyzer

10m 10.4m 10.8m 11.2m 11.6m 12m 12.4m

-60

-40

-20

0

20

40

60

[s]

[m/s 2] Time(acc) - InputWorking : Input : Input : FFT Analyzer

10m 10.4m 10.8m 11.2m 11.6m 12m 12.4m

-60

-40

-20

0

20

40

60

[s]

[m/s 2]

Damage size 30%, location 2/4Damage size 30%, location 1/4

Undamaged

• Wave propagation

- impact at fixed end : 9.8 ms

- 1st arrival at free end : 10.3ms

- reflection from damages : -

- 2nd arrival at free end : 11.1ms

• Wave propagation

- impact at fixed end : 9.8 ms

- 1st arrival at free end : 10.3ms

- reflection from damages : -

- 2nd arrival at free end : 11.1ms

1111Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea

MethodsFactor of errors

Freq. domain

Mode shape

Time domain

Impact load O × O

Weight of the sensor O × O

Boundary condition O O O

Shaker instability × O ×

Resolution O × O

Inequality of the beams O O ×

Temperature O × ×

Noise of the sensor × O ×

• Effect of experimental errors

1212Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea

Conclusions

• Under 10% damages can be found by various detection methods

with simulation, however it is impossible by experiment because

of practical problems.

• Not exact location of damages but existence of them can be detected by frequency domain method.

• Simulation of mode shape method find even small damages, however its experimental result is insufficient to detect damages.

• Time domain method can find the location of relatively large damages.