REINFORCED CONCRETE : Dr. Supratic Gupta (14 sessions)(14 ...web.iitd.ac.in/~sbhalla/cep726.pdf ·...

CEP 726

STRUCTURAL ENGINEERING LABORATORYUpdated on 14 Oct 14

REINFORCED CONCRETE : Dr. Supratic Gupta(14 sessions)(14 sessions)

Structural Dynamics : Prof. A. K. Jain( )(07 sessions)

SMART MATERIALS AND D S h Bh llSMART MATERIALS AND : Dr. Suresh BhallaSTRUCTURES(07 sessions)

© Dr. Suresh Bhalla, Department of Civil Engineering, Indian Institute of Technology Delhi. This material is only for students of CEP 726 at IIT Delhi. No part of this material can be copied, transmitted or reproduced without written permission of the copyright holder.

INTRODUCTION TO SENSORS AND DEVICES

PIEZOELECTRIC SENSORS

ELECTRICAL STRAIN GAUGES

ACCELEROMETERS

DIGITAL MULTIMETER (DMM)

LCR METER (LCRM)

OSCILLOSCOPE


ELECTRICAL STRAIN GAUGES (ESG)Metal grids

εSR=

Δ

Polyimide plastic film

εgSR

=

Vo

ESG, RRo

Voltage recording d i

Ro Ro

device


Vi

PIEZOELCTRIC MATERIALSPIEZOELCTRIC MATERIALSDirect Effect

+++++++++++Mechanical Stress Electrical Charge

T TT T

Converse Effect

Electric Field Mechanical Strain

ElongationE


PIEZOELCTRIC MATERIALS(Constitutive relations)

TS 1= Ed+Strain

Stress Electric field

E3

2EY

S11

1 = 331Ed+w

E3

1

2

3333 ED Tε= Td+

T1

lh

3333 ED ε 131Td+Charge density

Electric field

Stress


Used for sensor applicationszero

STRAIN MEASUREMENT BY PIEZOELCTRIC MATERIALS

TdD 1313 TdD =QV =Parallel Plate

VKVST

⎟⎞

⎜⎛

33εw1

32 C

V =Parallel Plate Capacitor

VKVYhd

S pE=⎟

⎟⎠

⎜⎜⎝

=31

331

T1

lh

w

Voltage α Strain© Dr. Suresh Bhalla, Department of Civil Engineering, Indian Institute of Technology Delhi. This material is only for students of CEP 726 at IIT Delhi. No part of this material can be copied, transmitted or reproduced without written permission of the copyright holder.

Voltage α Strain

ELECTRO-MECHANICAL MPEDANCE (EMI) TECHNIQUE(EMI) TECHNIQUE

A PZT patch is surface bonded on a structure using high strengthadhesive and excited at high frequency (30-400 kHz) by animpedance analyzer.

E3

Structural Impedance

A PZT Patch bonded to a structure

A simple physical model of system (Liang et. al, 1994)

p

structure

PZT PATCH ACTS AS SENSOR AND ACTUATOR SIMULTANEOUSLY

PZT patch

E31

32

Structural l

hw

l

Z Z

Impedance

φφω

ωj

o

otj

o

tjo e

uF

eueF

uFZ

&&&=== − )(

MECHANICAL IMPEDANCE

Unique function of structural stiffness, damping and mass

Liang et al. (1993, 1994): Based on 1D analysis (for skeletal structures)

⎥⎦

⎤⎢⎣

⎡−⎟

⎠⎞

⎜⎝⎛

⎟⎟⎠

⎞⎜⎜⎝

⎛+

+= EE

a

aT Ydl

lYdZZ

ZhwljY 2

3123133

tanκκεωElectric Admittance =

g ( , ) y ( )


Structure

Impedance Analyzeror LCR meter

M t tStructure Measurements at multiple frequencies form “signature”PZT patch

Electromechanical Admittance, Y = G + B j

form signature

Conductance Susceptance

, j

0 0007

0.000750.008

0.0004

0.00045

0.0005

0.00055

0.0006

0.00065

0.0007

Con

duct

ance

(S)

0.002

0.003

0.004

0.005

0.006

0.007

Sus

cept

ence

(S)

0.0003

0.00035

140 145 150 155 160 165

Frequency (kHz)

0

0.001

140 145 150 155 160 165

Frequency (kHz)

0 0002

0.0004

0.0006

0.0008

0.0004

0.0008

0.0012

-0.0006

-0.0004

-0.0002

0

0.0002

Stra

in

-0.0008

-0.0004

0

Stra

in

-0.00080 5 10 15 20

Time (s)

-0.0012

0 5 10 15 20

Time (s)


PIEZO-ELECTRIC SENSOR ELECTRICAL STRAIN GAUGE

10/14/201410

ACCELEROMETERSF(t)

Seismic mass

y(t) m

)()()( tFxykxycym =−+−+ &&&&

k c

mass

zxy =−

Base mass

x(t) mb

2&&

For the limiting case of very small frequency rat

ωω << 2nzx ω−≈nωω <<

* Very expensive (Typically over Rs 25, 000)

* Low bandwidth

© Dr. Suresh Bhalla, Department of Civil Engineering, Indian Institute of Technology Delhi. This material is only for students of CEP 726 at IIT Delhi. No part of this material can be copied, transmitted or reproduced without written permission of the copyright holder.10/14/2014 11* Very fragile

2

3

4

5

0 4

0.6

0.8

1

PIEZO-PATCH ACCELEROMETER

-2

-1

0

1

2

-0.1 0 0.1 0.2 0.3 0.4 0.5Volta

ge (V

)

-0.4

-0.2

0

0.2

0.4

-0.1 0 0.1 0.2 0.3 0.4 0.5Volta

ge (V

)

Time (s)

-5

-4

-3

-1

-0.8

-0.6

60

16

18

ACCELEROMETER

30

40

50

e (V)

8

10

12

14

ge (V

)

PIEZO-PATCH

10

20

Volta

ge

0

2

4

6

8Vo

ltag


00 20 40 60 80 100

Frequency (Hz)

00 20 40 60 80 100

Frequency (Hz)10/14/2014

12

SENSING OF FLEXURE

C i ++Vo

Compression

Tension

++

++--

-- D

e s o

++ ++-- --

10/14/2014

Vo

C i ++Vo

SCompression

Tension

++

++--

--Stop

Sbott

D

++ ++-- --

Vo

)( SSkV SS botttop +)( botttopo SSkV +=D

SS botttop +=φ

10/14/2014 14

kDV

DSS obotttop =

+=φCurvature

kDDVoltage α Curvature g

TDS 2004BTecktronix oscilloscope

34411AAgilent digital

QDA 1000Quazar TechnologiesAgilent digital

multimeterQuazar Technologieshttp://ww.quazartech.com

Four channel, real-time, low on resolution IMPORTED

Single channel, near real-time, high on resolution IMPORTED Eight channel, real-


Eight channel, realtime, high on resolution, INDIGENOUS

CONCRETE VIBRATION SENSOR (CVS)( )

CVS is a ready to use packaged sensor for dynamic response measurement developed especially for reinforced concrete structures such as buildings and bridges.

Sensors embedded in RC test structure

16


10/14/201416

© Dr. Suresh Bhalla, Department of Civil Engineering, Indian Institute of Technology Delhi. This material is only for students of CEP 726 at IIT Delhi. No part of this material can be copied, transmitted or reproduced without written permission of the copyright holder.10/14/2014 17

COMPARISON-ACCELEROMETER AND CVS

ACCELEROMETER

CVS


DYNAMIC FORCE SENSOR

Sensitivity = 25 mV/N In house lab product, cost only a

Technology has been transferred to INOV htt // i i

p , yfraction of the imported brand


http://www.inov.co.in

DIGITAL MULTIMETER (DMM)DIGITAL MULTIMETER (DMM)

Model 34411A

(Agilent Technologies)(Agilent Technologies)

http://www.agilent.com

•Can measure AC and DC voltages, resistance

U t 50 000 l d•Up to 50, 000 samples per second

•Can store 1million readings in the memory

•Six and half digit display


g p y

•Suitable for both static and dynamic mesurements

OSCILLOSCOPEOSCILLOSCOPE

Model TDS 2004BModel TDS 2004B

(Tektronix)

http://www.tektronix.com

•Can measure voltages as low as 2 mV

•Up to 1Giga samples per second

•Four channelsFour channels

•Download manual http://www2.tek.com/cmswpt/madetails.lotr?ct=MA&cs=mur&ci=16272&lc=EN


16272&lc EN

LCR METER (LCRM)

Model E4980 Precision LCRM

(Agilent Technologies)

http://www.agilent.comCan measure the resistive, inductive and capacitive components of any electrical circuit.

p g

XjRZelectrical +=Electrical Impedance

ωLX 1−=

BjGZ

Y +==1

Electrical Admittance

ωC


jZelectrical

TEACHING/ LEARNINGTEACHING/ LEARNING

VIRTUAL SMART STRUCTURES AND DYNAMICS LABORATORY

Project funded by MHRD, Govt. of India

DYNAMICS LABORATORY

Phase I completed

Experiments part of CEP 726 course


http://web.iitd.ac.in/~sbhalla

http://ssdl.iitd.ac.in/vssdl/home.htmlp


SMART MATERIALSAND STRUCTUREShttp://web.iitd.ac.in/~sbhalla/cep726.htm

EXPT 1 : Vibration Characteristics of Structures using Accelerometers and Surface Bonded Piezoelectric Sensors

Expt 1 of VSSDL (to be performed in remote mode from V 216)

EXPT 2 : Identification of High Frequency Modes of a Beam in “Free-Free” Condition using Electro-mechanical Impedance (EMI) Technique

Expt 2 of VSSDL (to be performed in remote mode from V 216)Expt 2 of VSSDL (to be performed in remote mode from V 216)EXPT 3 : Forced Excitation of Beam using Portable Shaker

Expt 3 of VSSDL (to be performed physically from V 211)EXPT 4 : Photogrammetry for Displacement MeasurementEXPT 4 : Photogrammetry for Displacement Measurement

Expt 4 of VSSDL (to be performed in remote mode from V 211)EXPT 5 : Vibration Characteristics of RC Beams using Embedded

Piezoelectric Sensors

(to be performed physically from V 211) Note: This is not Expt5 of Virtual Lab

EXPT 6 : Modes of Vibration of a simply Supported beam

(t b f d h i ll f V 211) N t Thi i t E t


(to be performed physically from V 211) Note: This is not Expt5 of Virtual Lab

EXPT 1 Vibration Characteristics of Structures using Accelerometers and

S f B d d Pi l i SSurface Bonded Piezoelectric Sensors

(This is also the expt 1 of the virtual lab. To be performed remotely from SSL V 216 through website of Virtual Smart structures and Dynamics Lab)

Excite the aluminium beam into free-damped vibrations (this is automatic)

Measure DC voltage across the PZT patch through oscilloscope DMM.

Transform the data to frequency domain using FFT (may use MATLAB in Structural Simulation Lab SSL (V 216)

Determine first natural frequency and damping ratio using half power band method

Repeat the above measurements using accelerometer (smaller beam)Repeat the above measurements using accelerometer (smaller beam).

Comment on the results of accelerometer and PZT patch.

Compare results with theory (frequency) and published data (damping ratio)

SUGGESTED READING: Paz (2004); Chopra (2001); Sirohi and Chopra (2000a)


SUGGESTED READING: Paz (2004); Chopra (2001); Sirohi and Chopra (2000a)

Manual of Experiment 1 of Virtual Smart Structures and Dynamics Lab.

DAMPINGD i i th di i ti ti f t i lDamping is the energy dissipation propertiy of a material or system under vibration/ dynamic loading.

H lf b d idth th d

ωω −

Half power band width method

nωωωξ

212 −=


EXPT 2 IDENTIFICATION OF HIGH FREQUENCY MODES OF BEAM IN “FREE-REE” CONDITION USING ELECTRO-MECHANICAL IMPEDANCE (EMI)CONDITION USING ELECTRO-MECHANICAL IMPEDANCE (EMI) TECHNIQUE (To be performed remotely from SSL V 216 through website of Virtual Smart structures and Dynamics Lab)

This is same as experiment 2 of virtual lab

Connect the wires of two PZT patches such that the two are in phase (same electrodes

PZT patch (on each face)

paired), hence axial modes are excited (already connected).

Obtain the plots of G and B vs frequency over (5-100 kHz) using LCRM. Identify the frequencies of axial modes and compare with theory.

Connect the wires of two PZT patches such that the two are in out of phase (oppositeConnect the wires of two PZT patches such that the two are in out of phase (opposite electrodes paired), hence flexural modes are excited.

Obtain the plots of G and B vs frequency over (5-100 kHz) using LCRM.

Identify the frequencies of axial modes and compare with theory.SUGGESTED READING P (2004) Ch (2001) N id d S h


SUGGESTED READING: Paz (2004); Chopra (2001); Naidu and Soh (2004a, b), Manual of Experiment 2 of Virtual Smart Structures and Dynamics Lab.

EXPT 3 FORCED EXCITATION OF STEEL BEAM USING PORTABLE SHAKER

(To be performed remotely physically from V 211through website of Virtual Smart structures and Dynamics Lab)

This is Expt 3 of Virtual lab

Compute the first three natural frequency of steel RC beam (take measurement of the dimensions) ISJB 150, 3.2m long.

Apply a sweep signal (10-40Hz) using the function generator (already set).

Measure DC voltage across PZT patch and carry out FFT in MATLAB.

Determine the natural frequency and damping ratio, compare and comment results with theory (for frequency) and published literature for damping ratio).

SUGGESTED READING: Paz (2004); Chopra (2001) Brownjohn et al (2003)


SUGGESTED READING: Paz (2004); Chopra (2001), Brownjohn et al. (2003)


EXPT 4 PHOTOGRAMMETRY FOR DISPLACEMENT MEASUREMENT

(To be performed remotely from SSDL V 211 through website of Virtual Smart structures and Dynamics Lab)

A BStationary frame of reference

This is same as Expt 4 of Virtual lab 100mmA B of referenceof Virtual lab

Take picture with IP camera.

C Reference attached to structure

Apply loads, keep taking measurements with dial gauge as well as recording pictures. Take at least 5 measurements.

Compute displacement from the pictures (vertical distance between A and C) using MATLAB or ADOBE photoshop (count pixels) or MS word.

Compare the displacement with that measured using dial gauge.

Plot load vs displacement from two systems side by side.

Comment on the accuracy and resolution of photogrammetry.SUGGESTED READING J i t l (2003) M l f E i t 4 f


SUGGESTED READING: Jauregi et al. (2003), Manual of Experiment 4 of Virtual Smart Structures and Dynamics Lab.

EXPT 5 VIBRATION CHARACTERISTICS VIBRATION CHARACTERISTICS OF RC

BEAMS USING EMBEDDED PIEZOELECTRIC SENSORSBEAMS USING EMBEDDED PIEZOELECTRIC SENSORS(To be performed in direct mode at V 211)

Note: This is not the experiment 5 of the virtual lab

Excite the beam into free-damped vibrations with a hammer gently

Measure DC voltage across the PZT patches (one embedded, other surface bonded), and accelerometer, in time domain through oscilloscope.

Transform the data to frequency domain using FFT (may use MATLAB in Structural Simulation Lab SSL (V 216)

Determine first natural frequency and damping ratio using half power band method.

C t th lt f f b d d t h l t d CVSComment on the results of surface bonded patch, accelerometer and CVS.

Compare results with theory (frequency) and published data (damping ratio)

SUGGESTED READING: Paz (2004); Chopra (2001)


( ); p ( )


EXPT 6 MODES OF VIBRATION OF A SIMPLY SUPPORTED BEAM

PZT sensor

supportsupport


Oscilloscope Impact hammer

EXPT 6 PROCEDURE: MODES OF VIBRATION OF A SIMPLY SUPPORTED

BEAM (T b f d di l V 211)BEAM (To be performed directly V 211)

2 3 4 5 6 71

Compute the first two natural frequencies of the beam theoretically before doing the experiment. Measure all dimensions of the beam

Excite the beam into free-damped vibrations with special impact hammer gently.

Feed the voltage from impact hammer to first channel of oscilloscopes.

Feed sensor responses to other channels of oscilloscopes.

Carry out FFT of both force and response, and obtain frequency response function (FRF) as the ratio of response to force Do this for all sensorsthe ratio of response to force. Do this for all sensors.

Obtain first two mode using absolute value of the real/ imaginary part of FRF, taking help from the frequencies computed in the first step (browse down to learn the procedure).

SUGGESTED READING: Paz (2004); Chopra (2001) Peter Avitable’s website:


http://macl.caeds.eng.uml.edu/umlspace/mspace.html

EXPERIMENTAL MODAL ANALYSISModal analysis is a process whereby the structure is described in terms of its natural dynamic characteristics, namely the natural frequencies, mode shapes and damping.natural frequencies, mode shapes and damping.

Voltage measuring device

Accelerometer

ISMB 150

Function Generator

Stinger

Shaker

Let us apply a sinusoidal signal of constant amplitude, but vary the frequency gradually.


TIME AND FREQUENCY DOMAINS

Time domainTime domain response

Natural frequenciesNatural frequencies Frequency

domain response

Fast Fourier Transform (FFT)

f


The frequency domain response is much easier to evaluate as compared to the time domain.

MODE SHAPESMODE 2

MODE 1 MODE 3

Mode shape is the deformation pattern of the structure at


p pwhen excited at a particular natural frequency.

FREQUENCY RESPONSE FUNCTION (FRF)FUNCTION (FRF)

It is the ratio of the output response (strain/ displacement/velocity/ acceleration of a structure (undergoing vibration) at a point to the force applied at the same or other point, at a particular frequency. Both the force and the response areparticular frequency. Both the force and the response are simultaneously measured.

φω

φω

ω j

o

otj

o

tjo e

Fu

eFeu

Fuh −

−

===)(

)(FRF (ω) : Unique function of

structural stiffness, damping and massand mass

In this experiment, we will measureIn this experiment, we will measure strain and hence our mode shapes will be strain mode shapes


p

MODE SHAPES FROM FRFhij = Response at ‘i’ due to force applied at ‘j’. ji, j = 1, 2, 3.

h11 = Response at “1’ due to force at ‘1’

h12 = Response at “1’h12 Response at 1 due to force at ‘2’

h13


MODE SHAPES FROM FRFSimilarly, we can experimentally derive:

h21 h22 h23Response at 2, point of impact varied.

and also

h h32 h33Response at 3, point of impact variedh31 h32 h33 of impact varied.

IF THE STRUCTURE IS LINEARLY ELASTICIF THE STRUCTURE IS LINEARLY ELASTIC,

WHAT IS THE RELATION BETWEEN: hij AND hji

MUST BE EQUAL SINCE MAXWELL-BETTI’S THEOREM STATES:

The displacement at a point due to unit load at the other point is


The displacement at a point due to unit load at the other point is equal to that at the other point due to unit load applied at the first point.

MODE SHAPES FROM FRF

h11 h12 h13 h11 h12 h13

h21 h22 h23 h21 h22 h23

h h h hh31 h32 h33h31 h32 h33


Real part of FRF Imaginary part of FRF

MODE SHAPES FROM FRFIn general, any one row can provide us all the mode ge e a , a y o e o ca p o de us a t e odeshapes. Let us use the imaginary part of the third row i.eh3j i.e the measurement point is same, excitation point is varied. In all, only one sensor required.

f1

h31 =h13h32 =h23 h33

MODE 1MODE 1f1

f1

ff2 f2

MODE 2

f2 f2

f2

MODE 3 ???


Try yourself….

MODE SHAPES FROM FRFSince hij = hjiij ji

Any one column can also be used in place of a row.

If say the third column is yused i.e hj3 i.e three measurement points, one excitation point Can useexcitation point. Can use three sensors with simultaneous

t d thmeasurements and thus acquire all data in a single go.gOr can also repeat three times with one sensor, each time changing position of the sensor. This is called as “roving” of


This is called as “roving” of sensors.

Flexural mode shapesFlexural mode shapesMODE SHAPE 1

33.3, 0.23766.6, 0.323 133.3, 0.294

166.6, 0.672

0 2

0.4

0.6

0.8

Vol

tage

(mV

)

0, 0 200, 00

0.2

0 50 100 150 200 250

V

Distance (cm)

33.3, 0.21566.6, 0.229

0.2

0.3

)

MODE SHAPE 2

0, 0 100, -0.0002

133.3, -0.193 166.6, -0.159

200, 0

-0.2

-0.1

0

0.1

0 50 100 150 200 250

Vol

tage

(mV

)


-0.3Distance (cm)

REFERENCES• Avitable, P. (2001), “Experimental Modal Analysis (A Simple Non-mathematical Presentation) ”

http://macl.caeds.eng.uml.edu/umlspace/mspace.html• Bhalla, S. and Soh C. K. (2004), “High Frequency Piezoelectric Signatures for Diagnosis of Seismic/ Blast Induced

Structural Damages”, NDT &E International, Vol. 37, No. 1 (January), pp. 23-33.g , , , ( y), pp• Brownjohn, J. M. W., Moyo, P. Omenzettor, P. and Lu, Y. (2003), “Assessment of Highway Bridge Upgrading by Dynamic

Testing and Finite-Element Model Updating”, Journal of Bridge Engineering, ASCE, Vol. 8, No. 3, pp. 162-172.• Chopra, A. (2001), Dynamics of Structures, Prentice Hall of India limited, New Delhi.• Jauregui, D. V., White, K. R., Woodward, C. B., Leitch, K. R. (2003), “Noncontact Photogrammetric Measurement of Vertical

Bridge Deflection”, Journal of Bridge Engineering, ASCE, Vol. 8, No. 4, pp. 212-222.• Naidu, A. S. K. and Soh, C. K. (2004a), “Damage Severity and Propagation Characterization with Admittance Signatures of

Piezo-transducers”, Smart Materials and Structures, Vol 15, 627-642.• Naidu, A. S. K. and Soh, C. K. (2004b), “Identifying Damage Location With Admittance Signatures of Smart Piezo-

Transducers”, Journal of Intelligent Material Systems and Structures, Vol 13, 393-403.• Paz, M. (2004), Structural Dynamics: Theory and Computations, 2nd ed., CBS Publishers and Distributors, New Delhi.• PI Ceramic (2006), http://www.piceramic.de• Sirohi, J. and Chopra, I. (2000a), “Fundamental Behaviour of Piezoceramic Sheet Actuators”, Journal of Intelligent Material

Systems and Structures, Vol. 11, No. 1, pp. 47-61.• Sirohi, J. and Chopra, I. (2000b), “Fundamental Understanding of Piezoelectric Strain Sensors”, Journal of Intelligent

Material Systems and Structures, Vol. 11, No. 4, pp. 246-257.• TML (2007), Tokyo Sokki Kenkyujo Co. Ltd., http://www.tml.jp/e , Tokyo.


CEL 726 STRUCTURAL ENGINEERING LABORATORY SMART MATERIALS AND STRUCTURES COMPONENT

(Conducted by Dr. Suresh Bhalla)

GENERAL INSTRUCTIONSGENERAL INSTRUCTIONS

1. After finishing work, all instruments/ tools/ consumables should be back to

the designated places.

2. No waste material should be left on the work table after finishing the

experiments. All devices, PCs and UPS should be switched off.

3. The laboratory is under video/ audio surveillance. Users found notcomplying with these instructions will be penalized in thecomplying with these instructions will be penalized in the evaluations.

4. A joint report of the experiment should be prepared and submitted in the

next laboratory class by each group. The standard format available at

htt // b iitd i / bh ll / 726 t dhttp://web.iitd.ac.in/~sbhalla/cep726report.docx

5. The main contents of the report should be Abstract, Experimental Details,

Results and Conclusions. Be very brief; use third person and past tense.

Do not show data in the report, only include the plots. For experimental

setup, include a well labelled picture of the set up. All pictures should be

compressed such that the final size of the document is less than 1MB.

6. Maximum length of report should be TWO pages only, printed on either

side of the A4 paper. p p

7. Students should save all the original data as well as the electroniccopy of the report for future use during the same course.

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