Merit Enckell presentation_PhD

Merit Enckell presents:Merit Enckell presents:Merit Enckell presents:Merit Enckell presents:
Lessons Learned in Structural Health Monitoring of Bridges
Using Advanced Sensor Technology
Opponent:
Professor Konrad Bergmeister,
Universität für Bodenkultur Wien, Vienna, Austria
Evaluation committee:
Professor Annika Mårtensson, Lund University (LTH), Lund, Sweden
Associate Professor Mario Plos, Chalmers, Gothenburg, Sweden
Dr. Sam Johansson, Hydroresearch, Täby, Sweden
Supervisor: Professor Johan Silfwerbrand, Royal Institute of Technology (KTH) and President
of Swedish Cement and Concrete Research Institute (CBI), Stockholm, Sweden
Co-supervisor: Dr. Jacob Egede Andersen, COWI AS, Kongens Lyngby, Denmark
2nd of December 2011, Stockholm, Sweden

MSc for the New Årsta Railway Bridge
Merit Enckell COWI A/S

General Introduction
• Research project with the support of National Railway Authorities
• A static study and a dynamic study
Merit Enckell 6th of December 2012 COWI A/S

Background
• Several projects with Fibre
…Optic Sensors

Appended papers
• Paper A
− Integrity monitoring of an old steel bridge
(Götaälvbridge)
• Paper B
− Book chapter (Emerging technologies)
• Paper C
− General experiences gathered
• Paper D
− Research project of a unique structure (The New
Årsta Railway Bridge)

Aim and scope of the Thesis
• Present a realistic state-of-the-art report on recent SHM activities, both
….advantages and disadvantages need to be high-lighted.
• Present and increase the knowledge around emerging and established sensor
….technology.
• Highlight the plentiful possibilities FOS monitoring do provide and capture
…..lessons learned.
• Show applications.
• Analyse the performance of the SHMSs on some selected bridges
• Use the results achieved so far in the SHM of the New Årsta Railway Bridge in
…..future maintenance planning of the bridge.
• Highlight the general results and give recommendations.
• Discuss and conclude the general knowledge.
• Limitation

Methodology
• Applied research
− Experimental research
− Practical problems in real
…world
− Observation and testing
• Concrete research
− Early age
− Long-term
• Documentation
− Systematic
− Photographs
• Crack detection
− Several systems
− Detect, measure & localize
…cracks
• Testing and trouble shooting
− Short-term, long-term testing
− Identification, elimination, modification

Structural Health Monitoring
SHM of a structure performs structural characterization and
damage detection over time in order to provide reliable
information regarding the integrity of the structure.
1934

Structural Health Monitoring System
• Sensors: permanent on the structure and portable system
• Transmission cables
• Data acquisition systems
• Data transfer and storage systems
• Data management: analysis, presentation, interpretation.
• Other; spare parts, fastenings, tools, testing equipment, manuals

Structural Health Monitoring System

Structural Health Monitoring System:
Other important issues
• System acquisition and installation
• Management and maintenance
• Adaptability
• Dismantling
• Environmental effects
• Safety cautions

Established technologies
Established technologies are well known and
have a proper long-term experience.

Emerging Technologies
Emerging technologies, on the other hand, are
science based innovations that have the potential to
create a new industry or transform an existing one.
Emerging technologies demand for new kind of
thinking in order to prevail and copy with them. They
are also characterized with certain ambiguity and
complexity as they are in accelerating change. ------->
New thinking is needed!!

Emerging Technologies
• Acoustic emission
• Radar technology
− Ground penetrating radar
− Interferometric radar
• Photogrammetry
• Corrosion monitoring
• Weight-In-Motion systems
• Infrared thermography
• Smart technical textiles

Fibre Optic Technologies
• General
• FOS
Merit Enckell COWI A/S

Fibre Bragg Grating (FBG)
• A region of periodic variation in the index of the fibre
core
• The wavelength corresponding to the grating field will be
reflected
• The reflected light is led back, analyzed and converted
into engineering units.
• SG &LG, temperature compensated
• Versatility compared to other sensors

Fabry-Perot sensors
• Intrinsic, extrinsic and in-line fibre etalon
• The extrinsic Fabry-Perot sensor is easy to build:
− An air-gap of a few microns or tens of microns
− Calibration needed
• Strain, displacement, pressure and temperature
• Temperature compensated
• Strain rosettes

Michelson and Mach Zehnder interferometers
• Easy to understand and manufacture
• Michelson Interferometer more common:
− Static and dynamic measurements
− LG sensor
− SOFO system
• Strain, temperature compensated, used in many
applications

Distributed sensors
Brillouin, Raman, Rayleigh scattering
• Brillouin:
− Strain and temperature
− Spontaneous or stimulated
• Raman
−Only temperature measurements
• Rayleigh
− static measurements to distances up to 70
meters
− dynamic measurements up to 7 metres

Crack detection
• Crack detection, localisation as well as crack
…width estimation
• DiTeSt system
− Cracks bigger than 0.5 mm detected and localised
− Delamination need to take place
− Götaälvbridge: About 5 km sensors installed
− Warning system

FOS technology equipment
• A special laser pointer
• An Optical Time-Domain Reflectometer
(OTDR)
• Fusion splicer

Suitability
• SG FOSs are suitable to measure local material
behaviour
• LG FOS are suitable to measure global behaviour
• SG sensors are also good to measure crack
widths of the existing cracks
• LG FOSs are suitable to either cast in concrete,
mounted on the concrete surface: not in
direct sunlight
• Also composite materials
• Distributed FOSs are suitable for large structures:
−bridges, pipelines, dams, roads, pavements and also
various geotechnical applications

Chosen Applications
SHM of the New Årsta Railway Bridge
– Unique structure, doctoral projects connected to the bridge
SHM of the Traneberg Bridge
– Historical aspects of monitoring in Sweden and benefits of
temporary monitoring
SHM of the Götaälv Bridge
– A large project with novel technology
SHM of the planned Messina Bridge
– Groundbreaking challenge, designing a SHMS for the biggest
ever planned bridge in the world

The New Årsta Railway Bridge
• Applied research with novel technology and without previous
..experience is really challenging and many mistakes were made
• A lot can be learned and it is essential to capture lessons learned in
..order to develop best practices and successful criteria for future
..projects

The New Årsta Railway Bridge
Most important experiences:
• Cracking was revealed
• SOFO sensors do show stable long-term behaviour,
• Data loss was caused by modest memory capacity
• Long-term function of SOFO sensors is excellent.
• Long-term effects like shrinkage and creep were studied.
15/04/05 18/04/05 21/04/05 24/04/05 27/04/05 30/04/05
-340
-320
-300
-280
-260
-240
-220
Date
Microstrain
Section B
BS6
BS7

The New Årsta Railway Bridge: Results
• During construction
05/05 06/05 07/05 08/05 09/05 10/05 11/05 12/05 13/05
-450
-400
-350
-300
-250
-200
Date
Microstrain
Section A: 2003
AS1 AS2 AS3 AS4 AS5 AS9X AS10X
After casting the whole sequence the formwork
is drawn apart and lowered down and cantilever
is affected by it's selfweigth and produces tensile
stresses in the sensors on the upper edges and
compressive sresses in the trough.
Pre-stressing under
several days increased
the compressive stresses
on the sensors in the upper
edge.The trough was only
slightly affected.
Sensor AS4 stops measuring after pre-stressing

The New Årsta Railway Bridge: Results
• Long-term monitoring for Section A
03/01/22 03/05/22 03/09/19 04/01/17 04/05/16 04/09/13 05/01/11 05/05/11 05/09/08 06/01/06 06/05/06 06/09/03 07/01/01
-1000
-800
-600
-400
-200
0
200
400
600
Date
Microstrain
Section A
AS1
AS5
AS9X
AS10X

Traneberg Bridge
• The old bridges were retrofitted by keeping the arches and
..reconstructing the pillars and the deck. A third bridge was built.
• Monitoring with small amount of sensors and thermocouples
..provided interesting information during the retrofitting progress.

Traneberg Bridge
• Short study
• Comparison/Verification
• Temperature study
• Interesting information from the construction in the 1930ies

Götaälvbridge
• Built in 1939, total length is 950 m.
• Large steel beam, concrete deck structure with combined road
..and light-rail: opening-able.
• Most important connection between the Gothenburg City and
..Hisingen for the city traffic.
• Dynamic effects as well as static loads.
• Steel girders suffer from fatigue and mediocre steel quality .
• Severe cracking and also a minor structural element collapse.

Götaälvbridge
Important issues
• Feasibility study
• Verification
• Installation
• Crack identification algorithm
..was developed
• New methods and procedures
..in installing, testing, modifying
..and improving the installed
..system
• Analysis: warning messages
• Numerous testing
• FAT, SAT

Messina Bridge
• The planned Messina Bridge will connect the coasts of Sicilia
..and Calabria in southern Italy.
• The length of the main span will be 3300 m, the total length
..of the bridge 3666 m, will carry a four lane highway
• The triple box concept for the deck, which is 68 m wide.
Important issues
• SHMS has been developed
..parallel to the design
• Integrated into a Management
..and Control System
• Service life calculation and point
..ranking assessment: to assist with
..long-term maintenance planning

General Results & Recommendation
• SHMS design is performed in collaboration with SHM experts and
structural engineers; different stakeholders may have various needs
that need to be taken into consideration.
• The database where statistical studies of parameters are easily
done is preferred. The statistical methods are a good tool in
revealing malfunctions in long-term monitoring.
• If sensors are installed on the surface of the measured structure,
they should not be in the solar radiation or covered with a material
that will raise the local temperature and give biased readings.
• There is a need for common programming platform/environment
in large projects. Commercially available, proven sensors.
• Data should be storied in compatible format for end users; this can
decrease the cost of analysis fundamentally.
• Less is more.

FOS related
• Use of FOSs is straightforward if some education and training is
given. It is essential to understand sensor performances and to
comprehend with given technical requirements and specifications.
• Guidelines.
• Cabling issues are important when handling with FOSs;
IP standard, protection and other requirements.
• Interrogators and DAUs should be adaptable and with appropriate
size of internal memory.
• If having problems with dirty connectors and light losses in a
harsh environment with a lot of dust, it is better to splice the
connections in order to minimise losses.
• Technical specifications for FOS are not standardised and
therefore complex to comprehend and compare. Attention is paid to
details.

Concrete
• Measurement should start when pouring the concrete to
formwork and go on at least 28 days.
• Strain measurements need to be performed frequently meaning
minimum every hour but preferably more frequently and do
measure temperature of the concrete at the same frequency.
• Environmental parameters like temperature and air humidity
need to be measured continuously. If solar radiation is suspected to
give even just a moderate contribution to structural behaviour, it
needs to be monitored or the daily pattern needs to be recognised.
• Every construction step like pre-stressing and removal of the
formwork is measured. If having several separated sections and
only one portable interrogator, it is recommended to rent another
interrogator or several units in order to measure all activities as this
will help a lot when analysing the data. If that is not possible, it is
important to evaluate the most important event to be monitored.

Discussion
• SHM in general
• Distributed FOS and crack detection
…techniques
• Emerging technologies
• FOS in general
• Concrete Monitoring
• Installation issues and practical problems

Contribution
• A huge amount of capital is invested in these SHMSs all over
the world and it is complicated to judge the meaningfulness,
significance and contribution of these systems.
• Engineering society should be more critical to its own actions:
better planning, well defined organizational responsibilities,
straightforward systems without over ambitions, redundancy
and quality assurance are needed for more sustainable solutions
that will in fact save capital and contribute to a positive image of
SHM.
• The importance of international collaboration
• Lessons learned are presented here: better understanding and
recommendation are given
• Better utilizing as well as research in the SHM field: capital can
be saved and effectiveness can be increased.

Conclusions
• Emerging technologies do provide high precision, high accuracy, stability
and redundancy.
• Design of SHMS is a delicate process. A general procedure is presented.
• Complex SHMS require combination of several techniques.
• A novel crack detection and localisation system based on Brillouin
scattering was developed, tested and implemented on the Götaälvbridge.
• Fibre Optic LG sensors were shown optimal to cast in concrete.
• Monitoring revealed cracking at the deck of the New Årsta Railway Bridge.
• Long-term effects like shrinkage and creep were studied in SHMS of the
New Årsta Railway Bridge. The existing codes and models are inaccurate
and need to be revised.
• SHMS at The Traneberg Suburban Bridge show that temporary monitoring
with small amount of sensors and thermocouples can be a valuable tool
during the retrofitting progress.
• Sensor production needs better quality assurance.
• An advanced SHMS has been developed for planned Messina Bridge.

Future research
• Research early age effects of concrete: Development of strength, Young's Modulus,
shrinkage and creep from pour of the concrete to loading and how stresses are
developing in a structure.
• The behaviour of the shrinkage and creep in long-term pre-stress concrete
structures need to be studied. Existing codes contain shortcomings and need to be
revised.
• Statistical methods were used successfully to locate cracks and more investigation
is needed if these methods can be used to control crack propagation as well. The
bridge deck of the New Årsta Railway Bridge should be installed with
thermocouples so that the temperature evaluation of the deck can be performed
and included in the future maintenance of the bridge.
• Compare the results from SHMS of the New Årsta Railway Bridge with other similar
structures.
• Development of general platforms for data processing including analysis should be
investigated. Many existing analysis programs are too general and immature and
cannot tackle the amount of data and complexity that is needed in data analysis.
• International collaboration and openness are needed: faster development: both
advantages and disadvantages need to be highlighted. Harmonisation of
vocabulary.

Publication January 2013
Book Chapter:Book Chapter:Book Chapter:Book Chapter:
"New and Emerging
Technologies in
Structural Health Monitoring"
Merit Enckell,Merit Enckell,Merit Enckell,Merit Enckell,
KTH & COWI A/SKTH & COWI A/SKTH & COWI A/SKTH & COWI A/S
Jacob Egede AndersenJacob Egede AndersenJacob Egede AndersenJacob Egede Andersen
COWI A/SCOWI A/SCOWI A/SCOWI A/S
Branko Glisic, Princeton UniversityBranko Glisic, Princeton UniversityBranko Glisic, Princeton UniversityBranko Glisic, Princeton University
JohanJohanJohanJohan SilfwerbrandtSilfwerbrandtSilfwerbrandtSilfwerbrandt, KTH & CBI, KTH & CBI, KTH & CBI, KTH & CBI

Thank you for your precious time!Thank you for your precious time!Thank you for your precious time!Thank you for your precious time!

Merit Enckell presentation_PhD

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