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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - INFRASTAR (Innovation and Networking for Fatigue and Reliability Analysis of Structures - Training forAssessment of Risk)

Teaser

Summary

Civil infrastructures are the basis of socio-economic wealth for modern societies and concrete is the most used material in volume in the world. However, a series of limitations currently hamper innovative solutions in the asset management of civil infrastructures. One of the most prevalent issues, which directly influences the life expectancy of concrete structures, is fatigue. Although fatigue has been investigated for years for steel structures, recent findings suggest that concrete structures are also significantly subjected to fatigue, which could lead to premature failure. A second issue relates to the current technological means to measure fatigue on civil structures like bridges and wind turbines, as these are outdated, imprecise and inappropriate. Finally, while structural reliability methods have been widely applied in some industrial applications (e.g. for offshore oil and gas structures, bridges exposed to fatigue, and wind turbines), practical application of probabilistic methods still needs theoretical and practical developments.
INFRASTAR aims to develop knowledge, expertise and skills for optimal and reliable management of structures. The generic methodology is applied to bridges and wind turbines in relation to fatigue, offering the opportunity to deal with complementary notions while addressing three major challenges: 1) advanced modelling of concrete fatigue behaviour; 2) new non-destructive testing methods for early aged damage detection; and 3) probabilistic approach of structure reliability under fatigue. INFRASTAR improves knowledge for optimising the design of new structures, more realistic verification of structural safety, and more accurate prediction of the future lifetime of the existing structures.

Work performed

WP1: monitoring and auscultation
- State-of-the-art on fatigue sensors.
- CWI experiments, testing/improving electronic setups, data processing.
- Comparison with fibre optic and other NDT methods, analytical expression of the strain profile.
- Crack Opening Displacement measurement, one cable tested, comparison with ultrasonic and optical measurements.
- Optimal quantity of data in acquisition, combination/fusion of signal features, evaluation of feature extraction and data fusion.
- Review of NDT techniques, analysis of a one-year road bridge monitoring data set, laboratory trial tests.
WP2: structural and action models
- State-of-the-art on fatigue of concrete and steel elements and components of bridges and wind turbines.
- Preparation of an experiment on reinforced UHPFRC to built resistance models.
- Case studies: Chillon, CrÃªt de l\'Anneau, New little Belt bridges.
- Combination of Ultimate Limit State and Fatigue Limit State in order to estimate reliability levels in bridges.
- Multiscale coupling: Combination of Discrete Element Method and Finite Element Method.
- Validation of the use of a Representative Elementary Volume (DEM) to model high number of cycles.
- Explicit modelling of cyclic loading (experiment).
- Numerical study (offshore wind farm), global sensitivity analysis of gravity based foundation fatigue loads, uncertainty and reliability assessment of concrete fatigue damage.
WP3: reliability approaches for decision-making
- State-of-the-art on structure reliability against fatigue.
- Preliminary probabilistic framework for reliability assessment of reinforced concrete structures.
- Stochastic model for fatigue of concrete, stochastic action effect model.
- Fatigue Reliability analysis of CrÃªt De lâ€™Anneau Viaduct.
- Test of Kriging meta-modelling to evaluate time variant reliability problems.
- Monitoring data of St Vallier bridge.
- Statistical analysis on fatigue data.
- Risk assessment towards decision support tools for operation and maintenance ongoing.
- Risk assessment model for application to icing events for wind turbine.
- Implementation of pre-posterior Bayesian decision theory.

Final results

Project 1 focuses on CWI method for long-term structure health monitoring through portable and commercial devices to be developed and fabricated.
Project 2\'s contributions are:
- Developing a better sensing system and a strain transfer model for quantification of crack openings (DFO).
- Comparing early damage detection capabilities of DFO to other sensors.
- Investigating the effect of long-term fatigue loading on the strain transfer.
Project 3 evaluates automated NDT techniques and developed data fusion algorithm to determine adverse changes in the structure. Different features were extracted from embedded ultrasonic sensors, and fuzzy based fusion technique was implemented to improve the overall damage/change detection.
Project 4 presents a monitoring strategy to deal with reinforced-concrete bridge decks prone to fatigue damage; this provides engineers with a novel reliable method to evaluate fatigue safety. This strategy shall enhance existing codes and extend bridge service duration for sustainable use.
Project 5 deals with an optimal monitoring planning for existing structures. In case of fatigue, UHPFRC can be applied. Therefore, focus is put on resistance of reinforced UHPFRC element. Thus, replacement of structure can be avoided leading to more economical and ecological solution.
Project 6 proposes a procedure for prediction of lifetime of bridges using extreme values theory. The study shows the need to combine traffic loading with extreme environmental actions. The open access algorithm is expected to be applied to different structures with a contribution to Eurocodes.
Project 7 develops 2 numerical methods (cyclic implicit and innovative cyclic explicit methods) to predict the lifetime tilting behaviour of Offshore Wind Turbines under cyclic loading conditions. They have been qualitatively tested and will increase the reliability of the wind turbine design.
Project 8 deals with Fatigue Limit State assessment of Offshore Wind Turbine foundations. The sensitivity analysis revealed the most significant input parameters to reduce uncertainty in fatigue load predictions. Uncertainty modelling and reliability assessment are demonstrated and the safety against a fatigue-critical sea state is evaluated.
Project 9 develops a probabilistic framework for fatigue reliability assessment of concrete structures. A stochastic material model is developed based on fatigue test data and a stochastic load model is to be developed. A methodology using the models is expected for wind turbine and bridges.
Project 10 aims to provide a new and efficient methodology for time-dependent reliability analysis, to apply new statistical methods, and to provide a practical and efficient maintenance and monitoring framework for existing structures using structural health monitoring.
Project 11 develops methods for risk assessment with focus on adverse events. Sensors and condition monitoring systems are identified for decision-making. Mitigation measures will be identified and linked to the inspections. Bayesian networks will be used to implement the decision models.
Project 12 focuses on efficient repair actions for prolonging the service life of structures, and on determination of structural and damage detection system influencing parameters regarding value of information. This leads to cost efficient, reliable and safe strategies for maintenance.