Copy of Hemant Presentation 6 Oct

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Structural Health Monitoring and Damage

Detection of Structures

Presented by Guided by

Hemant Kumar Vinayak Dr. S.K. Thakkar

Dr. Ashok Kumar

Dr. Pankaj Agrawal

Department of Earthquake Engineering

Indian Institute of Technology

Roorkee, UA

Ph.D. Research Proposal



Presentation Overview

Introduction

Objectives Methodology involved

Experimental setup details

Plan of work



Structural Health Monitoring (Definition)

Focuses on techniques of :

Identifying the existence of damageIdentifying the location of damage

Estimating the magnitude of damage

Introduction (Contd..)



Structural Health Monitoring (Application)

Civil Infrastructure (Bridges, Highway, Buildings etc.)

Air Craft and Missile Structures

Space Structures

Land/ Marines Structures

Introduction



Project Proposal (Contd..)

Objectives

Present an overview of Damage Detection and Structural

Health Monitoring methods for buildings. Establish a correlation between damage in the model with

its known dynamic characteristics.

Comparative study of damage detection techniques for

building structures Develop methodology of damage detection and health

status in pre and post earthquake scenario using Non-

destructive Evaluation (NDE) techniques



Literature review

1. Literature review-

Identification of various methods

Selection of experimental procedure

Identifying the set of controlling parameters that are

need to be computed through experimentation



Methodology Involved (Contd..)

Changes in basic modal

properties

Dynamically measured

flexibility

Updating structural

model parameters

Frequency changes Comparison of flexibility

changes

Optimal Matrix update

methods

Mode shape changes Unity check method Sensitivity based

update methods

Mode shape curvature/

Strain mode shapechanges

Stiffness error matrix

method

Eigen structure

Assignment methods

Changes in modal energy,

Kinetic energy

Effect of residual

flexibility

Hybrid matrix update

methods

Changes in measured

stiffness matrix

Vibration based damage detection methods (Review by Doebling)



Structural Health Monitoring (Method for

Current Research)

Changes in basic model properties at each level of damage

during the experiment:

frequency

Mode shapes,

Modal strain energy,





Determine

Stiffness from displacement versus load graph

Natural frequency, mode shape and damping ratio from freevibration test. Damping from logarithmic decrement

Natural frequency, mode shape and damping ratio from

forced vibration test. Damping ratio will be determined from

half power band width methodMode shapes - The data acquired will coupled with the model

generated in ARTeMIS software



Methodology involved (Contd..)

Structural Health Monitoring (Method for

Current Research, Contd..)

Level of

damage in %

Hysteresis

Loop Load vs.Deflection

curve

Mode shapes Hysteresis

damping

Natural

frequency

Negligible

Light

Moderate

Heavy



Damage indices Methodology (Contd..)

Most traditional

indicator

Displacement ductility

Koh Integrity index

DisPasquale E and

Cakmak A.S.

1990

Maximum deformation

Skaerbaek P.S.

1996

Drift ratio

Park R 1996 ;

Bachmann H 1996

Stiffness ratio

ui

di

i S

S

S !

yield

d Q

Q Q

max!

H Di max Q

!

f irstyield

failureM Di

U/!

max,

,1

T i

initial T i Di !




Nagar, A ;1995,

Bernal D; 1992,

Ghobarah, A;1999

Flexural damage rotation

SARCOF Damage Indicator

Kraetzig W et al

2000

Softening index

max

0

K

K Di !

0

5.0)(1

EI

t EI Di

!

o

d

E

E Di ! 1




Modal assurance criteria

Normalised area

difference

Relative difference

§§

§!

jun j

jd n j

j

un jd n j

MAC 22

2

)()(

])()([

J J

J J

dx N A D ud ´ ! J J

un j

un jd n jn j R D

)()()(

J J J !

Ewins 1984 Salawu and Williams 1994



Model 1 A concrete cantilever column subject to lateral load

Experimental Setup Details



Model 2 A single story plane frame subject to lateral load

Experimental Setup Details



Model 3

One bay subject to uniaxial load

Experimental Setup Details (Contd..)



Model 4

Experimental Setup Details (Contd..)



Plan of Work

Jan 2004 to Oct 2004 i) Course work

ii) Comprehensive exam

iii) Literature review

Oct 2004 to Dec 2005 i) Fabrication of Models

ii) Testing of Models

Jan 2006 to Jun 2006 i) Analysis and Presentation of result

July 2006 to Dec 2006 i) Writing of PhD Thesis



Publications

Thank you



Future central monitoring station




Changes in basic modal properties

Frequency changes (Review by O.S. Salawu)

Loss of stiffness - When measured natural frequencies are substantially lower

than expected

Damage Causes - Support failure, crack propagation, shear failure and overload

causing internal damage

Degree of reduction - Dependent on the position of the defect relative to modeshape for a particular mode of vibration





Equation of motion

[ [k] - [2[M] ]{J } = {0}

[ (k+Hk) - ([2 + H [2 ) [M] ]{J + HJ } = {0}

Stiffness depends upon -Property of materials - Modulus of Elasticity E, Density V

Dimension of element - b, d, L

Damage induction in the structure



Mode shapes of undamaged and damaged steel frame infilled with

unstiffened thin steel plate shear panels - Prion and Rezai 1996




Modal strain energy change MSEC

i j

i ji jd

i jMS E

MS E MS E

MS ECR

!

Undamaged modal strain energy MSEij = JiTk j Ji

Damaged modal strain energy MSEdij = Jd

iTk j J

di





Mode shape changes

West 1984 - Changes in Modal Assurance Criterion to localize structural damage

Fox 1992 - Graphical comparison of relative changes in mode shapes

Cobb and Liebst 1997 - Prioritizing sensor location based on eigenvector

sensitivity analysis

Skjaeraek 1996 - optimal sensor location for damage detection based on

changes in mode shapes using substructure iteration method





Mode shape curvature/ strain mode shape changes

Utilizes relationship between curvature and bending strain for beams plates

and shells

Pandey et al 1991 - Changes in mode shape curvature can be a good indicator

for Fem beam structure.

Chance et al. 1994 - Numerically calculating curvature from mode shapes

resulted in unacceptable errors. Measured strains improved the resultdramatically.

Chen and Swamidas (1994), Dong et al (1994), Kondo and Hamamoto (1994),

Nwosu et al (1995) and Yao and Change (1995)




Dynamically measured flexibility

Comparison of flexibility changes

Utilizes relationship between curvature and bending strain for beams plates

and shells

Pandey et al 1991 - Changes in mode shape curvature can be a good indicator

for Fem beam structure.

Chance et al. 1994 - Numerically calculating curvature from mode shapes

resulted in unacceptable errors. Measured strains improved the resultdramatically.

Chen and Swamidas (1994), Dong et al (1994), Kondo and Hamamoto (1994),

Nwosu et al (1995) and Yao and Change (1995)





Unit check method

An error matrix is defined which measures the degree to which

pseudoinverse relationship between the dynamically measured flexibility

matrix and structural stiffness matrix is satisfied

Lim 1990 - Proposes for locating modeling error and uses the location of the

entry with maximum magnitude in each column to determine the error location.

Lim 1991 - Defines a least square problem for the elemental stiffness changes

consistent with unity check error in potentially damaged members







Effect of Residual Flexibility

Represents contribution to the flexibility matrix from modes outside

measured bandwidth so that exact flexibility matrix can be related to

measured modes.

Doebling et al. 1996 - Technique to estimate unmeasured partition of residual

flexibility matrix .





Changes in Measured Stiffness matrix

Pseudoinverse of dynamically measured flexibility matrix.

Salawu and Williams 1993 - Used direct comparison of measured parameter to

estimate damage .

Peterson et al. 1993 - Proposed a method to use measure stiffness and mass

matrices to locate damage




Updating structural model parameters

Optimal matrix update methods

Pseudoinverse of dynamically measured flexibility matrix.

Salawu and Williams 1993 - Used direct comparison of measured parameter to

estimate damage .

Peterson et al. 1993 - Proposed a method to use measure stiffness and mass

matrices to locate damage

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