European COoperation in the field of Scientific and Technical Research
1
Group Project 5
STRUCTURAL CONDITION EVALUATION OF PRESTRESSED CONCRETE STRUCTURES
BASED ON ACOUSTIC MONITORING
Co-ordinator: Stanisław RADKOWSKI
Working Group 3 - "New assessment methods"
European COoperation in the field of Scientific and Technical Research
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Participiants:
• Warsaw University of Technology - ������������ ����
• KWH Bautechnologen AG - ������� ���� ����� ������ ����������
• AGH University of Science and Technology - �����������������
• Poznan University of Technology - ����ł�� ������� ��� ���������
• Bouwdienst Rijkswaterstaat and Advitam - � �� !��������"#��� ������� ������ � ����������
• Budapest University of Technology and Economics (BUTE) -!�$�%�&�����
• National Technical University of Athens - ' �������� ������
European COoperation in the field of Scientific and Technical Research
3
Problem:To evaluate the structural condition of prestressedconcrete structure by means of vibro-acoustic monitoring and by improving the applicability of the dynamic evaluation techniques
Basic assumption – increase and decrease of prestressing forces are accompanied by a change of stress distribution in the cross-section of concrete structure. The parameters of propagation path will change due to this phenomena.
European COoperation in the field of Scientific and Technical Research
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What is the frequency stucture of a pulse?How it depends on: technical state and failure evolution?
WARSAW UNIVERSITY OF TECHNOLOGYThe Faculty of Automotive and Construction Machinery Engineering
European COoperation in the field of Scientific and Technical Research
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Kielce measurement – prestressedconcrete beam, bending force (changeable) applied in middle, measuring vibrations exceeded with impulse. Various prestressed beams examined.
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change of phase velocity
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European COoperation in the field of Scientific and Technical Research
7
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European COoperation in the field of Scientific and Technical Research
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change of group velocity
amplitude modulation of carrier function
before failure - dispersion phenomena
European COoperation in the field of Scientific and Technical Research
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European COoperation in the field of Scientific and Technical Research
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European COoperation in the field of Scientific and Technical Research
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Conclusions:
• Presented results were achieved in laboratory tests.
• Assumed models were confirmed by results achievedfor two different sets of beams.
• To make this method mature for application, method must be tested and verified on a real structure.
European COoperation in the field of Scientific and Technical Research
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– SoundPrint ® : continuous acoustic monitoring of prestressed structures. Monitoring of internal wire break activity
European COoperation in the field of Scientific and Technical Research
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Particular risks for pre or post tensioned structures
• Cables are very sensitive to– Corrosion– Fatigue
• These phenomenon remain hidden until final break of cable…
… and of bridge
Criticality of these risks is always high for cable based structures
European COoperation in the field of Scientific and Technical Research
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SoundPrint detects and localizes the sounds emitted by the energy released during wire
breakage
Sensors are distributed on the structure allowing a global and continuous monitoring
Structure Post tensioned structure
Cable / strand / wire
Acoustic sensor
Library of acoustic signature of known events allow identification of captured noises
European COoperation in the field of Scientific and Technical Research
21
SoundPrint allows early detection and localization of internal wire breaks
And filtering of ambient noise
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structure
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Sensors
Internet
Real time Internet access
Internet
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European COoperation in the field of Scientific and Technical Research
22
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• The signals were analyzed both in the time and frequency domain.
• The scope is to search for modulations in the signals
• Different parts of the signal (stationary – non-stationary) were examined with various frequency resolutions
• 2 Demodulation methods were used ( Hilbert & TeagerKaiser)
• The signals were decomposed by Empirical Mode Decomposition &
• Hilbert – Huang Transformation
European COoperation in the field of Scientific and Technical Research
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European COoperation in the field of Scientific and Technical Research
24
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European COoperation in the field of Scientific and Technical Research
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European COoperation in the field of Scientific and Technical Research
26
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European COoperation in the field of Scientific and Technical Research
27
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European COoperation in the field of Scientific and Technical Research
28
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European COoperation in the field of Scientific and Technical Research
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European COoperation in the field of Scientific and Technical Research
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Three test methods were developed and verified in the frame of the researches for prestressed concrete structures for the testing and assessment of the structure condition.
The test methods are based on:
time-modal analysis method,energy method of diagnostics, load power distribution analysis.
The elaborated research methods make the use of the analysis of vibroacoustic signals.
The vibration signals are taken from the tested structure and these have a form of decaying free vibrations.
The structure was excited by impact force .
One can distinguish the several basic steps of the investigations.
Initial investigationsBasic testsVerification tests
In parallel with the basic investigations thefollowing investigations:
• Static load tests• The ultrasonic tests• Auxiliary investigationswere carried out.
In addition, the FEM model of the beam was elaborated, and itis planned to use the BEM model as well._______________________________________A part of these investigations will be continued if the project is completed.
Two sets of beams were worked out and made:• The first set consisted of the beams with a different controlled initial
prestress
• The second set consisted of the beams with introduced initial imperfections that simulated a different degradation degree (structure integrity loss).
Basic Tests
were realized by a training system on the prestressed beams.
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conditionevaluationof tested object.(detection of:
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We can use the time integrated average R(f) frequency in order toassess the stress loss in the structures. (highest value of the correlation coefficient).
In order to detect the integrity loss of structures the following three parameters are suitable:
• Amplitude normalized total R(f) frequency deviation• Normalized R(f) frequency deviation • Frequency deviation rate.
The determination of the representative symptoms and their sensitivity require an individual approach for each test type of the structure.
The symptoms limit values of the representative symptoms on the basis ofexperimental data should be assessed.
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belka A0b nap. 00kN (w ym. pkt 3 ; odp.pkt. 3)
0
0,5
1
1,5
2
2,5
3
3,5
0 1000 2000 3000 4000
cz�stotliwo�� [Hz]
a R
MS
[m/s
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mz
cz kz
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Zale�no�� przepływu energii od stanu obci��enia i stanu technicznego - na
podstawie maksymalnej mody drga� gi�tnych - belka A4d, wymuszenie p. 4, pomiar drga� - czujnik p. 1
2.00E-10
1.20E-09
2.20E-09
3.20E-09
4.20E-09
5.20E-09
6.20E-09
7.20E-09
0 5 10 15 20 25 30 35
Obci��enie belki [kN]
Jedn
ostk
owa
Daw
ka E
nerg
ii [J
/kg]
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DRGANIA GI�TNE BELKI ELBETOWEJ A4d, punkt 1 -
pobudzenie impulsowe w p.4 - maksymalna ampl.
1.00E-111.01E-092.01E-093.01E-094.01E-095.01E-096.01E-097.01E-098.01E-09
0 5 10 15 20 25 30 35
Obci��enie belki [kN]
Jedn
ostk
owa
mak
s.D
awka
Ene
rgii
[J/k
g]
JDE bezwł. JDE strat JDE spr��.