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03 October2011

ACOUSTIC METHODS FOR THE ASSESSMENTOF FIRE DAMAGE IN CONCRETE STRUCTURES

Prepared By: ABERA MAMO JALETA(749383)

Supervisor:PROF. ROBERTO FELICETTI

POLITECNICO DI MILANO

FACOLTA DI INGEGNERIA CIVILE, AMBIENTALE AND TERRITORIALE

MASTER OF SCIENCE IN CIVIL ENGINEERING

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Objectives1

NDT Techniques for Fire Damage Assessment2

Indirect UPV Test to Damage & Undamaged Concrete3

Results and Discussion4

Overview

Conclusion and Recommendation6

Improvement of Refraction Methods5

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Objectives1

the objectives of fire damage assessment in concretestructures are:

to determine the residual bearing capacity of concrete

structures after fire.

to inspect and identify the type and extent of the

damage and get up and running the service again

quickly.

to determine and compare the restoration or

replacement costs

It requires to develop fast and reliable

of assessment techniques

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NDT Techniques for Fire Damage Assessment2

Rebound Hammer Hammer and Chisel

Drilling Resistance

VisualInspection

Chemical Methods

Impact- Echo Testing

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Shows excellent potential for testing fire damagedconcrete

Very sensitive

Truly non destructiveAble to average the inherent heterogeneity of concrete

Ultrasonic Pulse Velocity Test

To obtain the properties ofmaterials by measuring thetime of travel of stress wavesthrough a solid medium

RE

L

Cont

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Direct transmission (Maximum energy is propagated)Semi-direct Transmission (Itis less sensitive as compared to direct transmission)Indirect Transmission (least sensitive out of the three arrangements)

Cont

The receiving transducer get signal of only about 2% - 3% of amplitudethat produce by direct transmissionMeasuring layered materials(like fire damage Materials)The interpretation needs to be improved

Transducer Arrangement

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E R1 R3R2 R4

1

2

3

4

1

1

V20

V20

z

X = distance

T = time

Velocity

Damagedmaterial

Pristinematerial

too long

X

Principle of the UPV indirect method: X t curves

R

too slow

The slope is governedby the UP Velocityof the deepest layer

crack

minimumtravel time

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ContApplication of Refraction Method

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Correction for offset Problems

Cont

Transducer with a conical tip has been found to be very successfulto measure offsets.

y = 0.2443x

-10

0

10

20

30

40

50

-50 0 50 100 150 200

X-T Curve

Conetansiducers

-20

0

20

40

60

80

100

-100 0 100 200 300 400 500

Normal Transducers

NormalTransducers

y = 0.2443x - 7.0626

y = 0.2443x

-20

0

20

40

60

80

100

-100 0 100 200 300 400 500

Normal Transducers

Cone transiducres

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Indirect UPV Test to Damage & Undamaged Concrete3

Size 580 X 330 X 130mm C50 concrete panels

Pristine Concrete Panel SpecimenFire Damaged Concrete Panel Specimen

Damaged panels had been exposed to a marked thermal gradient (>5C/mm) by heating them on the one side (Tmax = 800C) whilekeeping cold the opposite side with a fan

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0

10

20

30

40

50

60

70

8090

100

0 50 100 150 200 250 300 350 400

Time

Distance X

50 KHz

Indirect transmission method on the undamaged specimen

0

20

40

60

80

100

120

0 100 200 300 400 500

Time

Distance X

27kHz

The transit times recorded,t, are plotted against thedistance between

transducers, X

Transit time, t, versus the distance, X Transit time, t, versus the distance, X

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0

50

100

150

200

0 100 200 300 400

Time

Distance X

50kHz

Path-1 (50KHz A)

path-2 (50KHz A) 0

50

100

150

200

0 100 200 300 400

Time

Distance X

50kHz

Path-1(50KHz B)

Path-2 (50KHz B)

0

50

100

150

200

0 100 200 300 400 500

Time

Distance X

27kHz

Path-1 (27KHz A)

path-2 (27KHz A) 0

50

100

150

200

0 100 200 300 400

Time

Distance X

27kHz

Path-1(27KHz B)

Path-2 (27KHz B)

Indirect transmission on fire damaged specimen

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Results and Discussion4

The big scattering of the result is due to the sensitivity of ultrasonic pulsevelocity test method in presence of cracks or defects.

The regularity of the obtained X-T plot with different probes validate thedata consistency

The conservative damage depth is 65mm recorded with 50kHz transducer inB-direction.

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0

2

4

6

81

2 34

56

7

8

9

10

11

12

13

14

1516

171819

202122

23

24

25

26

27

28

29

30

31

3233

3435 36

Comparison of 27kHz with 50kHz

Amplitud (50KHz)

Amplitude(27Khz)0

0.1

0.2

0.3

0.4

0.51

2 34

56

78

9

10

11

12

1314

1516

171819

202122

2324

25

26

27

28

29

3031

3233

3435 36

Comparison of 27kHz and 50kHz

transducers

Amplitude(50KHz)

Amplitude(27KHz)

5 Improvement of Refraction Methods5

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ContImprovement of the refraction method depends on:

Incident angle at which the compression wave generatedThis section presents the design and testing procedure of angle wedges forgenerating optimum wave parameters

Rubber wedgesWedge materials

The experimental evidence suggests that Natural rubber has more benefit forwedge material, due to its low velocity

i l f bb d

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ContExperimental setup for rubber wedges

0.00

1.002.00

3.00

4.00

5.00

6.00

-80 -30 20 70

a

mplitude(mV)

angle (deg)

Undamaged - 1st peak plain

30

35

40

45

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

-80 -30 20 70

amplitude(mV)

angle (deg)

Damaged - 1st peak plain

30

35

40

45

Amplitude versus angle for 27kHz emitter sensor

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Cont

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

-80 -30 20 70

amplitude(mV)

angle (deg)

Undamaged - 1st peak

plain

30

35

40

45

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

-80 -30 20 70

amplitude

(mV)

angle (deg)

Damaged - 1st peak plain

30

35

40

45

Amplitude versus angle for 50kHz emitter sensor

The optimization of wave parameter starts when the transmission method is

changed from direct to Indirect-transmission (almost at an angle greater than 80)

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Cont

Amplitude Vs Distance x on damagedconcrete panel

Amplitude Vs Distance x on pristineconcrete panel

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6. The combination of different ND technique, as a mean for improving the reliability andthe sensitivity range of the material inspection.

Conclusion and Recommendation6

5. The validation of data obtained depends on regularity of the obtained X-T plot.

4. Repeating the measurement by swapping the two probes or shifting the measuringdirection can definitely contribute to check the reliability of the acquired data

3. Improvement of wave parameters in a fire damaged member is limited to shorter

distance between the two probes.

1. The pulse attenuation in fire damage is due to increased number of micro-

cracks and the consequent decay of material elastic response

2. The selection of wedge materials depends lower pulse velocity and high acousticimpedance

7. Further studies are needed to optimize the size and shape of the wedges and theircoupling with both the sensors and the inspected member.

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Comment and QuestionEND

Thankyou!!

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Application of Refraction method