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09/11/2017
1
Project co-funded by the EU under H2020
ACOUSTIC EMISSION (AE) FOR STRUCTURAL HEALTH MONITORING
Jon WatsonInfrastructure DirectorMistras UK
Dr. Athanasios AnastasopoulosVice PresidentMistras Group Hellas A.B.E.E.
1st SENSKIN Workshop, 8 Nov. 2017, Brussels
Why Structural Monitoring?
• Health monitoring - performance vs modelling
• Fatigue assessment – stress and load cycles from strain
• Crack detection, location and monitoring
• Cable and post tension wire break detection
• Structural movement especially bridge bearings
• Monitoring during construction – temporary works
• Land slide / Rock fall detection, early warning and monitoring
• Corrosion monitoring
• Impact – bridge strikes
• Weather and earthquake loading Main Benefits• Ensure and Increase safety
• Increase life and availability of structure
• Reduce operating costs
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Monitoring Experience and Applications
1st SENSKIN Workshop, 8 Nov. 2017, Brussels
• Bridges- Aging assets- Strengthening schemes- New build
• Civil nuclear
• Military structures
• Buildings/car parks
• Oil and Gas- Process- Storage (LNG/liquids)
• Offshore structures- O&G- Wind energy
Monitoring and Data Outputs
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Monitoring and Data Systems
© Mistras Group 2017 www.mistrasgroup.com
Many different systems to meet the monitoring needs, between £1k - £500k
1st SENSKIN Workshop, 8 Nov. 2017, Brussels
Monitoring Technologies
• Acoustic Emission
• Displacement or movement
• Rotation
• Strain (resistance or Fibre Optic)
• Vibration / acceleration
• Weather stations (wind, temp, rain etc)
• Dynamic and static measurements
• Weigh in motion
• Total station – remote laser movement monitoring
• Corrosion monitoring
- Local pH
- Local humidity
- LPR corrosion potential
Any Sensor
e-mail1st SENSKIN Workshop, 8 Nov. 2017, Brussels
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Sensors, Gauges and Prisms
Many different sensors to get the data you need to manage your structure
1st SENSKIN Workshop, 8 Nov. 2017, Brussels
© Mistras Group 2017 www.mistrasgroup.com
According to ASTM, the term Acoustic Emission refers to “the class of phenomenawhereby transient elastic waves are generated by the rapid release of energy fromlocalized sources within a material, or the transient waves so generated”.
DEFINITION AND BASIC PRINCIPLES
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THE AE SIGNAL
91st SENSKIN Workshop, 8 Nov. 2017, Brussels
• Basic signal features describing signal shape are calculated, recorded and analyzed in real-time!
• Waveforms themselves can also be recorded.
Real-time evaluation or post processing analysis with graphs and location of AE
Time Driven Data (threshold Independent) usually RMS vs. Hit Driven Data (Threshold Dependent)
Crack initiation
Shock wave detected by sensor
BURST TYPE OF ACOUSTIC EMISSION SOURCES IN STRUCTURAL INTEGRITY APPS
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LINEAR LOCATION OF SOURCES
Source Close to sensor 1: Note the difference in arrival times Source in the middle: Time difference equals zero
1 2
Χ
L
ΑΕ SOURCE
Χ=1/2(L-VΔΤ)
1st SENSKIN Workshop, 8 Nov. 2017, Brussels
LABORATORY EXAMPLE I – NECESSITY of DAMAGE EVALUATION TECHNIQUE
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LOADING & CONVENTIONAL APROACH
Displacement-Time
AE ?
• Cracks are not visible until late stage loading ...Not at all in case of repair
• Load Displacement Curve does not permit damage characterization until almost final failure ...
Load–Displacement Load vs. Time
1st SENSKIN Workshop, 8 Nov. 2017, Brussels
LOADING & AE APROACH
Displacement-Time
AE Energy Release Rate provides Real Time info on damage built up and accumulation at early stage ...
Load–Displacement Load vs. Time
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DAMAGE CHARACTERIZATION BY MEANS OF AE
AE parameters evolution vs. time (Load vs. Time Curve Superimposed)
4 DAMAGE STATES:
0-550 sec const. energy (18e6 αJ) and slope & low amplitude.
550-1180 sec energy increases up to 6,7e8 αJ, higher slope & amplitudes
1180-1600 sec energy jump 2,3e9 αJ & amplitude increase
1600 sec to the end max energy 2,6e9 αJ. Different slope
1st SENSKIN Workshop, 8 Nov. 2017, Brussels
LABORATORY EXAMPLE II
1
6 2
12 5
4
3
7
8
9
10
1114 13
AE sensors position at Front Side .AE sensors position at the back Side of
the beam.
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DAMAGE LOCATION AND CHARACTERIZATION
▪ Absence of located events in the center –increased density of located events with orientation of the cracks under development – well correlated with VT
▪ Graph indicating the time vs. x position of damage indicative of damage progression vs. load/time (start at center then at edges)
1st SENSKIN Workshop, 8 Nov. 2017, Brussels
INDICATIONS AND DAMAGE EVALUATION PRIOR VT & AT EARLY STAGE
STATISTICAL EVENTS DISTRIBUTION INDICATIVE OF SHEAR FAILURE
DAMAGE LOCATION AND CHARACTERIZATION
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ΑΕ System AE sensors1st SENSKIN Workshop, 8 Nov. 2017, Brussels
AE SET UP
AE ACTIVITY PER COLUMN DURING COMPLEX DYNAMIC LOADING OF BUILDING
• The majority of the AE activity, around 98%, is emitted from columns 1 and 2 recorded during both positive and negative loadings (during negative only for columns 3 and 4).
• The AE activity starts at certain loading level, due to past loading simulating earthquake of 0.30g.
• The absence of AE activity during the accidental load hold at relative high load levels at time between 5000-5800sec, is worth noting.
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Top
Base
Top
Base
C1
C2
C3
C4
DAMAGE EVALUATION & CHARACTERIZATION PER COLUMN DURING COMPLEX DYNAMIC LOADING OF BUILDING
10/11/05 – Post failure assessment
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Examples of Wire Break Monitoring of Cables
Ben Franklin Suspension Bridge, USAManhattan Suspension Bridge, NYC, USA
Ben Franklin Suspension Bridge , USA
Humber Suspension Bridge , UK
R&D Project at Columbia University
1st SENSKIN Workshop, 8 Nov. 2017, Brussels
Steel Structure Monitoring
Steel girder bridge, M4 motorway over River Thames
Lowestoft orthotropic steel deck lifting bridge
Orthotropic deck fatigue monitoring Avonmouth Bridge M5 Motorway
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“Semi-global” Monitoring
Steel Box Girder Monitoring
Steel girder bridge, M6 motorway
M8 motorway, Glasgow, Scotland
Steel girder butt weld testing A38(M), Birmingham
Bidston Moss, M53 motorway
Steel girder bridge, A34(M) motorway
White Cart Viaduct, M8 motorway
Gravelly Hill, M6 motorway
Summary Steel Fatigue ResultsM48 Severn Bridge England
Ben Franklin Suspension Bridge, USA
Royal Navy Dock, Scotland
Ben Franklin Suspension Bridge , USA
Severn Suspension Bridge , UK
Active (minor) fatigue like sourceat 10.8m along the girder
Example fatigue location results and results summary
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Concrete Structure Monitoring
Concrete bridge, M25 Motorway South England Concrete bridge, A14 Cambridge England
Concrete bridge, M4 Motorway London Concrete bridge, M50 Motorway West England
Summary Concrete Monitoring ResultsM48 Severn Bridge England
Cable Stay Bridge, USA
Active concrete micro fracture
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Summary Concrete Monitoring Results
1st SENSKIN Workshop, 8 Nov. 2017, Brussels
Summary Concrete Monitoring Results
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DISCUSSION & CONCLUSIONS
➢ Acoustic Emission can be used for direct assessment of Structural Risk and Reliability for the applied conditions.
➢ Acoustics Emission deliver clear, accurate information from monitoring that helps engineers to - increase structural safety- assess condition of materials and structure- optimise asset management- maximise safe structural life- minimise whole life costs
➢ MG has extensive experience in structural monitoring and provides a complete service for any monitoring application – on a large or small scale
Project co-funded by the EU under H2020
ACOUSTIC EMISSION (AE) FOR STRUCTURAL HEALTH MONITORING
Jon WatsonInfrastructure DirectorMistras UK
Dr. Athanasios AnastasopoulosVice PresidentMistras Group Hellas A.B.E.E.
1st SENSKIN Workshop, 8 Nov. 2017, Brussels