Topics

Technical Reports

Journal of Analytical Engineering, Vol.37, Preface

2Vol.37 2015/1

Journal of Analytical Engineering, Vol.37, Contents

Vol.37 2015.1
02

Topic 104
Topic 206

Topic 308

Technical Report 1
14
Technical Report 2
A Damage Detection Technique by Distributed Strain Measurements using
Long-gage Fibre Bragg Grating Sensors

24

Kejian YANG, Ryo YONAO, Kazumi YAMAMOTO

Editor’s Note35

Jounal of Analytical Engineering, Vol.37

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Vol.37 2015/1

Jounal of Analytical Engineering, Vol.37

6Topic 2Vol.37 2015/1

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Journal of Analytical Engineering, Vol.37 Technical Report 111( 201410)

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164-0011
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Vol.37 2015/117

Journal of Analytical Engineering, Vol.37 Technical Report 1

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Vol.37 2015/1

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362 /I-4 pp.1-11 1985.10
3) L. B. Lucy A numerical approach to the testing of thefission hypothesis, The Astronomical Journal, 82,
pp.1013-1024, 1977
4) R. A. Gingold, J. J. Monaghan, Smoothed Particle
Hydrodynamics Theory and Application to Non SphericalStars, Monthly Notices of the Royal Astronomical Society,181, pp.375-389 19775)
2005.
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19

Journal of Analytical Engineering, Vol.37 Technical Report 1

No.20130021 2013.12
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No.20080006 2008.39) M. Meyer, M. Desbrun, P. Schröder, Alan H. Barr Discrete
differential-geometry operators for triangulated 2-manifolds,
In Visualization and Mathematics III pp.35-57 2003
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Vol.53A pp.597-604 2007.3

No.655/V-48 pp.47-61 2000.8

20Vol.37 2015/1

Journal of Analytical Engineering, Vol.37 Technical Report 2(IABSE) 2014

A Damage Detection Technique by Distributed Strain Measurements using
Long-gage Fibre Bragg Grating Sensors
Kejian YANG
Chief Engineer of SeismicEngineering Department,
KOZO KEIKAKU Eng. Inc.,Tokyo, JapanRyo YONAO
Section Chief of SeismicEngineering Department,
KOZO KEIKAKU Eng. Inc.,Tokyo, Japan

Kazumi YAMAMOTOManager of SeismicEngineering Department,
KOZO KEIKAKU Eng. Inc.,Tokyo, Japanykj@kke.co.jp

ryo@kke.co.jp

kazumi@kke.co.jp

Kejian Yang, born 1962, received
his civil engineer degree ofDoctor of Philosophy fromTOHOKU Univ., Japan. His mainarea of research is related toComputational Mechanics andStructure Health Monitoring.

Ryo Yonao, born 1977, received
his civil engineering degree fromSAGA Univ., Japan. His mainarea of research is related toseismic analysis of bridges,dams, facilities, equipment andother civil structures.

Kazumi Yamamoto, born 1961,
received his civil engineering
degree from NIHON Univ.,
Japan. His main area of researchis related to the inter-action of soil
and structure in seismicengineering.

Summary
In this paper, a damage detection technique for flexural structure using strain measurements fromlong-gage fibre Bragg grating (FBG) sensors for structural health monitoring (SHM) wasdeveloped. An experimental investigation of flexural beams based on distributed long-gage fibreoptic sensors was carried out. A method of damage detection for flexural structure from distributed
dynamic strain measurements was proposed and verified. Furthermore, a parameter study of thedamage detection index proposed by author by means of analysis of experimental data wasperformed and the possible range for practical utility of the damage detection method wasconfirmed here. The above damage detection technique could be applied to the health monitoring ofbridge and other flexural structures.
Keywords: structural health monitoring long-gage fibre Bragg grating sensor damage detection
technique distributed dynamic strain measurements flexural structures.

1.

Introduction

Regarding the on-going development of available fiber optic sensing techniques, FBG sensor innature holds the excellent ability to provide a measurement having higher precision and measuringstability. A series of lab experiments and theoretical studies for the utilities of distributed long-gage
FBG sensor system by authors has been performing since 2006. Such works include theoretical andexperimental studies by Li & Wu [1][2][3] and Yang et al. [4][5], the actual survey for an oldunder-use RC bridge named KAWANE located in Ibaraki Japan from 2008 [6][7].
On the bases of above studies, a damage detection technique for flexural structure using strain
measurements from long-gage FBG sensors was developed. An experimental investigation of
flexural beams based on a distributed sensing system was carried out. A method of damage
detection for flexural structure from distributed dynamic strain measurements was proposed andverified. Furthermore, a parameter study of the damage detection index proposed by author bymeans of analysis of experimental data was performed and the possible range for practical utility ofthe damage detection method was confirmed here. This damage detection technique could beapplied to the health monitoring of bridge and other flexural structures.

24

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2.
2.1

-The long-gage FBG sensor of which the effective sensing gauge length can be extended to several
centimeters or meters through special packaging and broadening was developed by authors shownin Fig.1 [2][3][4]. It was applied to civil structures as a kind of distributed strain sensing techniqueby connecting a group of long-gage sensors in series shown in Fig.2.

Fig. 1: A packaged long-gage FBG sensor

Fig. 2: Distributed long-gage FBG sensing system
2.2--Vol.37 2015/125

Journal of Analytical Engineering, Vol.37 Technical Report 2(IABSE) 2014

Fig. 3: Static method for damage detection

2.3
As we known, the structure mode shape is determined by the nature dynamic feature of a structure
which will be no change by whatever the loads were in static way or dynamic way and wherever theloads were located. If our distributional strain measurement can be described as an evaluation ofstructure modes, the above idea of static damage detection method could be developed into adamage detection technique independence from load conditions.
2.3.1 MMSVrr

Hd
lp-(H mp ())

lrm (irjr )

(1 )
--m

Fig. 4: Macro-strain measurements of Beam structure26

Vol.37 2015/1

r

H mp ( ) is the macro-strain frequency response function between the measurement from the mth

long-gage sensor and the excitation at the pth degree of freedom.
rHlpd ( ) is the displacement frequency response function between the measurement from theposition of the lth long-gage sensor and the excitation at the pth degree of freedom.
lr

is the rth mode shape at the pth degree of freedom.

The subscript r is assigned to the rth mode.
mhm is the mth distance from inertia axis.

hm
Lm

( 2)

The relative ratio of all components of the combination of macro-strain magnitude of frequency
response functions from all FBG sensors can construct a vector as:
1r, 2r ,T, mr ,(3)

named by modal macro-strain vector(MMSV). It is verified that the time-series and frequency
response of the measured macro-strain versus displacement response and the MMSV versus modeshape share the same relationships. Therefore, we can use MMSV as an index value of dynamic
method for damage detection similar to the normalized strain in static method for damage detection.
2.3.2 The damage detection techniqueSensor Number

30

1020MMSV

Macro-strain

1551000051015Sensor position

20Frequency

Fig. 5: Macro-strain magnitude of frequency response functions
A damage detection procedure for structures can be described as follows:
1) Install a distributional long-gage FBG sensing
system on a bridge or other flexure structure.

32.52) Get time histories of macro strain of each sensor.

4) Record the MMSV of each sensor for every
measurement as Fig.6.
5) Analysis the variation of MMSVs shown in Fig.6
and give a health diagnosis of the structure.

MMSV

3) Calculate macro-strain magnitude of frequency
response functions as Fig.5.

sensor32
1.5

sensor4
sensor2
sensor1

1sensor50.5
0The numbers of test

Fig. 6: Damage detection by MMSV
Vol.37 2015/1

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Journal of Analytical Engineering, Vol.37 Technical Report 2(IABSE) 2014

3.

3.1

Fig. 7: Section of specimen

Fig. 8: Size of specimen-Fig. 9: Distributional FBG sensors
28

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were recorded and thecalculation of MMSV foreach sensor was done inevery time of measurement.
According to the analysis ofthe variation of measured
MMSVs, it is clear that theproposed dynamic damage
detection technique could
identify the even slight
defect effectively.

3.2

Experiment results

Fig.10 shows the specimens
with distributed long-gage
FBG sensors, interrogator

L3L4L2L5L1

named Modal Macro Strain Vector(MMSV) introduced in above section for
all five sensors in a specimen.
It is obvious that in case of intact beam theMMSVs of each sensor keep almost nochange and in case of defective beam theMMSVs of the sensors near the position ofcrack become abrupt change clearly. It
provides us a useful and effective method
to identify the damage of structure whichis independence from any load conditions.
It is feasible to apply on damage detectionof bridge or other flexural structures forstructure
healthmonitoring.

Vol.37 2015/1

Ratio of MMSVmax. vs. MMSVave.

Fig. 11: MMSV for damage detection

Fig. 10: Experimental verification
and a personal computer. The softwarefor data processing directly wasdeveloped and installed in this computer.
Fig.11 shows the results of damage
detection by these experiments. There
are the results of 16 times of two
specimen beams, in which 8 times arefor an intact beam and 8 times are for a
defective beam. The horizontal axis ofFig.11 is the number of experiment,
which the first 8 times from 1 to 8 areresults of intact beam and the second 8times from 9 to 16 are results fordefective beam, while the vertical axis ofFig.11 is the damage identification index

without damage
with damage

L2

L3

L4SensorFig. 12: Sensitivity of MMSV for damage detection
29

Journal of Analytical Engineering, Vol.37 Technical Report 2(IABSE) 2014

3.3
In order to elucidate the possible range for practical utility of proposed damage detection technique,some analytical studiesof experimental results
Table 1: Possible Range of MMSV for Damage Detection
were performed. AsshowninFig.12,
sensitivity of MMSV
for damage detection
was discussed andconcluded as follows.
In case of the test of
intact beams, the ratioof the maximum valueof MMSVs versus theaverage value of those
MMSVs are near
105% that all values
are less than 110%,while in case of thetest of defective beams,
the ratio of themaximum value of
MMSVs versus theaverage value of those
MMSVs are all larger
than 115%. It means
that, in practice use ofthis method, if thevalues of MMSVs ofmonitoring results arechanging within 10%,
it is probably theinfluence of noise orothercircumstancecondition, if the valuesof MMSVs of monitoring results are changing larger than 15%, it should be possibly occurrence ofsome damages of the monitoring structure.

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4.

Conclusions

The conclusions of this paper could be drawn as follows.
The results of a series of experiments verify the validity of proposed method of dynamic damage
detection for flexural structure using strain measurements from long-gage fibre Bragg grating (FBG)
sensors for structural health monitoring (SHM)
Modal Macro Strain Vector (MMSV) of structure can be used as a damage identification index.
Since the values of MMSV change abruptly even when a slight structure damage occur, proposed
method of dynamic damage detection could identify the damage of structure sensitively andeffectively.
Because the measured values of MMSV of a frequency even with 10% difference from the structure
natural frequency could also identify the damage as same accuracy as the exact ones, proposed
method of dynamic damage detection is a robust one with many superior features, it could be
widely used in damage identification of bridges and other flexural structures for structure healthmonitoring.

REFERENCES[1]

Li SZ. and Wu ZS., “A Non-baseline Algorithm for Damage Locating in Flexural Structuresusing Dynamic Distributed Macro-strain Responses”, Earthquake Engineering andStructural Dynamics, 36, 9, 2007, 1109-1125.

[2]

Li SZ. and Wu ZS., “Development of Distributed Long-gage Fibre Optic Sensing for
Structural Health Monitoring”, Journal of structural health monitoring, 6, 2, 2007, 133-143.

[3]

Li SZ., Wu ZS. and WATANABE T., “A Health Monitoring Strategy for RC FlexuralStructures based on Distributed Long-gage Fibre Optic Sensors”, Journal of Applied
Mechanics, 10, 2007, 983-994.

[4]

YANG KJ., ARAKI H., YABE A., WU ZS. and Li SZ., “The Optimum Length of Longgage FBG Sensors for Structural Health Monitoring of Flexure RC Members”, The
Proceeding of 4th China-Japan-US Symposium on Structural Control and Monitoring,Oct.16-17, 2006, HangZhou.

[5]

YANG KJ., ARAKI H., YABE A., and WU ZS., “Load Identification of Flexure RC
Structures using Distributed FBG Sensing System”, The Proceeding of 3th International
Conference on Structural Health Monitoring on Intelligent Infrastructure (SHMII-3),
Nov.14-16, 2007, Vancouver.

[6]

YANG KJ., YABE A., YAMAMOTO M., ARAKI H. and WU ZS., “The Evaluation of
KAWANE Bridge by Distributed FBG Sensors and by FEM Analysis”, The Proceeding of4th International Conference on Structural Health Monitoring on Intelligent Infrastructure(SHMII-4), July22-24, 2009, Zurich.

[7]

YABE A., YANG KJ. and MIYAMOTO A., “Sensitivity Analysis for Deteriorating Bridges
using Bus Acceleration Sensors”, IABSE Conference on Information and Communication
Technology for Bridges, Buildings and Construction Practice, September9-11, 2009,
Bankok.
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GHE-SJournal of Analytical Engineering, Vol.37 Editor’s Note

http://www.kke.co.jp/kaiseki/Vol.37 2015/1

35

kaiseki@kke.co.jp

Journal of Analytical Engineering Vol.37 2015.1