Merit Enckell presents:Merit Enckell presents:Merit Enckell presents:Merit Enckell presents:

Lessons Learned in Structural Health Monitoring of BridgesUsing 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

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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)

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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

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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

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

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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

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Structural Health Monitoring System

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Structural Health Monitoring System:Other important issues

• System acquisition and installation

• Management and maintenance

• Adaptability

• Dismantling

• Environmental effects

• Safety cautions

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

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Emerging TechnologiesEmerging 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!!

Merit Enckell 6th of December 2012 COWI A/S

Emerging Technologies• Acoustic emission

• Radar technology

− Ground penetrating radar

− Interferometric radar

• Photogrammetry

• Corrosion monitoring

• Weight-In-Motion systems

• Infrared thermography

• Smart technical textiles

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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

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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

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Michelson and Mach Zehnder interferometers

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• 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

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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

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FOS technology equipment

• A special laser pointer

• An Optical Time-Domain Reflectometer (OTDR)

• Fusion splicer

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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

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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

Merit Enckell 6th of December 2012 COWI A/S

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

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The New Årsta Railway BridgeMost 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.

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Section B

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The New Årsta Railway Bridge: Results• During construction

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Section A: 2003

AS1 AS2 AS3 AS4 AS5 AS9X AS10X

After casting the whole sequence the formworkis drawn apart and lowered down and cantileveris affected by it's selfweigth and produces tensilestresses in the sensors on the upper edges andcompressive sresses in the trough.

Pre-stressing underseveral days increasedthe compressive stresseson the sensors in the upperedge.The trough was onlyslightly affected.

Sensor AS4 stops measuring after pre-stressing

The New Årsta Railway Bridge: Results• Long-term monitoring for Section A

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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

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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.

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Traneberg Bridge

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• 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.

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Götaälvbridge

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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.

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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.

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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.

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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.

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Discussion• SHM in general

• Distributed FOS and crack detection …techniques

• Emerging technologies

• FOS in general

• Concrete Monitoring

• Installation issues and practical problems

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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.

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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.

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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.

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Publication January 2013

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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 Andersen Jacob Egede Andersen Jacob Egede Andersen Jacob Egede Andersen COWI A/SCOWI A/SCOWI A/SCOWI A/S

Branko Glisic, Princeton UniversityBranko Glisic, Princeton UniversityBranko Glisic, Princeton UniversityBranko Glisic, Princeton University

Johan Johan Johan Johan 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!