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Queensland University of Technology

CRICOS No. 00213J

An Improved Modal Strain Energy

Method for Damage Assessment

Presented By:

Buddhi L. WahalathantriD. P. Thambirathnam

T.H.T. Chan

S. Fawzia

CRICOS No. 00213Ja university for the worldrealR

Presentation Outline

• Introduction

• Theory: Strain Energy based Damage Indices

• Problem Identification

• Improved SE Method

• Results

• Conclusions & Future Work


Introduction

• Damage Detection

– Vibration Based Damage Identification Techniques

• Modal Strain Energy Method

• SE Method

– Damage Identification & Localization [Ref 6]

– Require first few modes to be measured and used

– False Alarms

– Not detect some damage locations (multiple damage)

– Improved SE Method


Theory: SE of a Euler Bernoulli Beam

• Strain energy of a Euler-Bernoulli beam: Mode

‘i’, Element ‘j’:

1 2 j N

Node 1 2 3 j j+1 N N+1

Distance 0 aj aj+1 L


SE based Damage Indices

• β1: Cornwell et al [Ref. 9]

• β2: Park et al [Ref. 10]


SE based Damage Indices

• β3: Li et al [Ref. 11] & Shih et al [Ref 12]


Problem Identification

• False Alarms

– At Nodal Points

• Indicates undamaged locations as damage

– Missing information

• Not detecting some damage locations

– Small damage severities

– Multiple damage locations

• Need higher mode addition


Improved SE Method

• New DI

– Minimise false alarms

– Improve damage detection

– Minimise number of modes

• Improved DI: β4


Improved SE Method

• Modification Function: MFij

– Using Mode shape curvature values

– Simply supported beam


Present Study Summarizes……..

• Simply Supported Beam

– Single Damage

• 28 Damage Cases

– 7 Damage Locations: L/8, 9L/56, 3L/16, L/4, 3L/8, 7L/16, L/2

– 4 Damage Severities: 10%, 20%, 30%, 40%

– Multiple Damage Cases (Two Damages):

• 32 Damage Cases

– By varying both Damage Locations and Severities

• Multiple Spans (Two Spans)• 30 Damage Cases


Method

• Data Analysis

– Data Analysis Software

• MATLAB Environment

• By Developing a Programme

• With GUI

• Supports 3 Types of Input (to date) data

– Experiment Results (extracted mode shape values)

– FEM Results: ABAQUS & SAP 2000

• Simultaneous Analysis with different number of modes

• Ability to address Forward and Inverse Problem


Results

• Simply Supported Beam

– Single Damage with different;

• Damage Location (DL)

• Damage Severity (DS)

– Multiple Damages

• Case 1: DL1 = L/4, DS1 = 40%, DL2 = L/2, DS2 = 40%

• Case 2: DL1 = L/4, DS1 = 10%, DL2 = L/2, DS2 = 40%

• Two Span Beam

– Damage locations: Mid Spans


Results: Comparison of DIs

• β1 vs. β4

– Simply supported beam [Ref. 12]

– DL: L/2

0

2.5

5

7.5

10

12.5

15

0 0.7 1.4 2.1 2.8

β1

Distance: x (m)

β1:Mode 3

-2

0

2

4

6

8

10

0 0.7 1.4 2.1 2.8

β4

Distance: x (m)

β4:Mode 3



• β2 vs. β4

– Simply Supported Beam

– DL1 = L/4, DS1 = 40%, DL2 = L/2, DS2 = 40%

-2

0

2

4

6

8

10

12

0 0.7 1.4 2.1 2.8

β4

Distance: x (m)

β4:Mode 2

0.98

1

1.02

1.04

1.06

1.08

1.1

0 0.7 1.4 2.1 2.8

β2

Distance: x (m)

β2:Mode 2



• β3 vs. β4

– Simply Supported Beam

– DL1 = L/4, DS1 = 10%, DL2 = L/2, DS2 = 40%

0.98

1

1.02

1.04

1.06

1.08

1.1

1.12

1.14

0 0.7 1.4 2.1 2.8

β3

Distance: x (m)

β3:Modes 1-5

-1

0

1

2

3

4

5

6

0 0.7 1.4 2.1 2.8

β4

Distance: x (m)

β4:Modes 1-5


Damage Index: β4

• Two Span Beam

– Damage at middle of each spans

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1.4 2.8 4.2 5.6

β4

Distance: x (m)

β4:Mode 1

-0.2

0

0.2

0.4

0.6

0.8

1

0 1.4 2.8 4.2 5.6

β4

Distance: x (m)

β4:Modes 1, 2 & 3


Damage Index: β4

• Potential to Damage Quantification

0

2

4

6

8

10

0 0.35 0.7 1.05 1.4

β4

Distance: x (m)

β4:Mode 1

DS=10%

DS=20%

DS=30%

DS=40%


Damage Index: β4

• Potential to Damage Quantification

0

2

4

6

8

10

0 5 10 15 20 25 30 35 40 45

β4

Damage Severity (DS%)

β4:Mode 1

x=0.4375 m

x=0.525 m

x=0.7 m

x=1.4 m


Conclusions

• Proposed Damage Index;

– Minimise False Alarms

– Improved damage detection

• Compared to other SE based methods

– Minimise Number of Modes

– Potential to Damage Quantification


Further Studies

• Improved Results with Noisy Data

– Up to 5% Noise

– Reinforced Concrete Beams

– Load Induced Damage Cases

• Need studies on;

– Damage quantification

Queensland University of Technology

CRICOS No. 00213J

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