This document describes a new method called acousto-elastical stress measurement for geotechnical online monitoring. It uses ultrasonic sensors to measure the running time of sound waves through a material, which changes based on the stress or load applied. A time-to-digital converter is used to precisely measure the running time. The method was tested in laboratory and field experiments to monitor stress in concrete structures and could enable low-cost, durable stress monitoring in various civil engineering applications.

1. Acousto-elastical stress measurement-a
new procedure for the geotechnical
on-line monitoring
F.-M. Jäger
fmj@ibj-technology.com
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Ingenieurbüro Jäger 1

2. Acousto-elastical stress measurement-which
is that ?
Transmitter Reciver
Ultrasonic
Ping
⇒ ⇒ ⇒ ⇒ ⇒ ⇒ ⇒ ⇒ ⇒ ⇒ ⇒
the running time is measured
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3. Acousto-elastical stress measurement-which
is that ?
Stress or load
Transmitter Reciver
Ultrasonic
Ping
⇒ ⇒ ⇒ ⇒ ⇒ ⇒ ⇒ ⇒ ⇒ ⇒ ⇒
the running time is measured
the new running time is smaller
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4. 1 Physical fundamentals
higher stress causes higher speed
the ultrasonic longitudinal wave
Cl = Speed of sound
 = Poisson's ratio
P = Density
E = Young's modulus (modulus of elasticity)
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5. Acousto-elastical effect
Stress
SPEED
TIME
PING
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6. acousto-elastical effect
Stress
SPEED
50°K Heating up  Run time increase 10,6 ‰
PING
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7. acousto-thermal effect
Stress
SPEED
50°K Heating up  Run time increase 10,6 ‰
PING
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8. The solution for the sensor
Measurement of the
running time
+ temperature
The ultimate solution for digital acousto-elastical
Sensors
TDC = Time -to-Digital Converter
Dimension 5 x 5 Millimeters
1-channel double resolution with typ. 45 ps
Up to 1 million measurements per second
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9. The solution for the sensor
Measurement of the
running time + temperature
TDC = Time -to-Digital Converter
The ultimate solution for digital acousto-elastical Sensors
•1-channel double resolution with typ. 45 ps
•Up to 1 million measurements per second
•Dimension 5 x 5 Millimeters
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10. The solution for the sensor
Measurement of the
running time + temperature
TDC = Time -to-Digital Converter
The ultimate solution for digital acousto-elastical Sensors
• 1-channel double resolution with typ. 45 ps
• Up to 1 million measurements per second
• Dimension 5 x 5 Millimeters
example
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11. 2 Sensitivy and factors of influence
running time
Sensor thickness 10 mm
running time change as function
of the temperature
3150 μs
-26°C 3050 μs temperature
+80C
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12. 2 Sensitivy and factors of influence
Sensor thickness
25 mm
the end of the
sensor is
1 Giga Pa
1 x 103 N/mm2
Runn time as function of the stress
Laufzeit = f (Spannung)
7780
7775
7770
7765
7760
7755
7750
7745
7740
7735
7730
0 10 20 30 40 50 60
Laufzei t ns
Runn time
26°C Stress
3050 Spannung μs MPa
80°C
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13. 2 Sensitivy and factors of influence
Speed of the ultrasonic wave as function of the stress
Stress ⇒
26°C 3050 μs C Independently of sensor thickness
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14. 3 Measurement under the hydraulic press
hydraulic press, concCrede
body and elastomeric bearing
equipment
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15. 3 Measurement under the hydraulic press
C
Stress concentration over the sensor
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16. 3 Measurement under the hydraulic press
Data Aqusition System DASYLab 9
experimental setup C
DASYLab 9 computation “sigma is”
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17. 3 Measurement under the hydraulic press
Methods of the
sensor assembly
primary bedding in
the concrete
secondary put in
boreholes / embed
into expansive
cement
experimental loads setting C
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18. 4 Field measurement at a building of the
federal motorway
the sensor
installation into
Boreholes
25 mm
diameter
stress sensor BBS_10_DS C
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19. 4 Field measurement at a building of the
federal motorway
Measurement of the running time
with ultrasonic material testing set
C
Measuring box with TDC
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20. 4 Field measurement at a building of the
federal motorway
⇒
running time
⇒
sigma / stress
⇒
temperature
⇒
sensor-serialnumber
Screen of the Windows program
for the measurement sigma
determination (stress)
C
Measurement equipment
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21. 4 Field measurement at a building of the
federal motorway
C
object of the
measurement
BAB 9, Munich-Berlin ⇒
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22. 4 Field measurement at a building of the
federal motorway
C
object of the
measurement
BAB 9, Munich-Berlin ⇒
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23. 4 Field measurement at a building of the
federal motorway
object of the
measurement
C
⇒
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24. 4 Field measurement at a building of the
federal motorway
object of the
measurement
27 reinforced
elastomeric
bearings
C
⇒
⇒
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25. 4 Field measurement at a building of the
federal motorway
object of the
measurement
27 reinforced
elastomeric
bearings
27 acusto-elastical
C
Cross section of the bridge
Reinforced elastomeric bearing
⇒
° ° °
sensor 1 sensor 2 sensor 3
sensors
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26. 4 Field measurement at a building of the
federal motorway
C
hydraulic lifting
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27. 4 Field measurement at a building of the
federal motorway
C
⇒
⇒
Bore hole for the sensor
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28. 4 Field measurement at a building of the
federal motorway
C
⇒
⇒
Preparatory hole
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29. 4 Field measurement at a building of the
federal motorway
C
Sensor inserted
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30. 4 Field measurement at a building of the
federal motorway
C
secondary mounting /
embed into shrink-free mortal
Sensor
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31. 4 Field measurement at a building of the
federal motorway
C
Elastomeric bearing assigned
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32. 4 Field measurement at a building of the
federal motorway
C
after hydraulic sinking
the first measurement under load
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33. 4 Field measurement at a building of the
federal motorway
C
bridges on the elastomer bearings
hydraulics cylinder dismounts
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34. 4 Field measurement at a building of the
federal motorway
C
sensor-lines up eastward
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35. 4 Field measurement at a building of the
federal motorway
C
sensor-lines up to the west
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36. 4 Field measurement at a building of the
federal motorway
C
⇒
⇒
mobile measurement or permanently
everything a question of the costs
⇒
⇒
all sensors inserted
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37. 5 Results of measurement
27
C
stress in concrete
100
80
60
40
20
0
1
3
5
7
9
11
13
15
17
19
21
23
25
bearing number
stress MPa
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38. 5 Results of measurement
40 N/mm2 traffic load change
Dynamic load measurement bearing 20
30 N/mm2
20 N/mm2
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39. 5 Results of measurement
traffic load change
50
45
40
35
30
25
20
15
10
5
0
. . . . . . . 10 secunds
00: 73: 31 05: 63: 31 04: 63: 31 03: 63: 31 02: 63: 31 01: 63: 31 00: 63: 31
0 r ebi er hcS
Dynamic load measurement bearing 20
40 N/mm2
30 N/mm2
20 N/mm2
s: ni m: h
4 measurements/sec; the new TDC more than 1000 are time faster
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40. 6 View on applications
advantage of the acousto-elastical stress measurement:
• Low cost on-line measurement
• Practically indestructibly
• No measuring range delimitation upward
• Measurement in the heap of debris and
fracturing zone
• Measurement in the water
• Inexpensive lost probe
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41. 6 View on applications
Rock stress measurement
Frac with expansive cements
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42. 6 View on applications
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43. 6 View on applications
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