TG3.1 - Reliability and safety evaluation: full-probabilistic and semi-probabilistic methods for existing structures

fib Task Group 3.1 (TG3.1) focuses on the reliability and safety evaluation of existing structures and focuses on the development of risk and reliability target levels for assessment and retrofitting, the full-probabilistic modelling of the structural safety and semi-probabilistic assessment methods for existing structures. In the framework of development of fib MC, TG 3.1 is revising also basis of structural design.

The TG aims to (i) resolve pending questions with respect to the full-probabilistic assessment and target safety levels for the assessment and retrofitting of existing structures, and (ii) support the risk and reliability related questions arising due to the developments in TG3.2, TG3.3 and TG3.4.

In probabilistic assessment of degrading structures, TG3.1 is cooperating with COM8, mainly through TG8.8.2.

Working topics include:

• Risk acceptance and decision-making for existing structures
• Probabilistic models and Bayesian updating framework for the assessment of existing structures
• Full-probabilistic and semi-probabilistic reliability analysis of new and existing structures

Convener
Miroslav Sykora

Co-Convener
Raphaël Steenbergen

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TG3.2 - Modeling of structural performance of existing concrete structures

It is widely understood and accepted that existing concrete structures are different entities to contemporary new concrete structures. There are numerous flexibilities inherent to the process of the design of new concrete structures and in their construction. Existing structures are entities that can, in principle, be interrogated and assessed to establish their actual nature and condition. However, such processes have their difficulties and uncertainties and it is in fact often very difficult to interrogate an existing structure. These difficulties increase when an existing structure has experienced damage or deterioration. Accordingly, substantial and different uncertainties remain with respect to existing structures and these uncertainties need to be taken into account in the structural assessment process.

During recent years Task Group 3.2 has distinguished three main areas relevant for the determination of the structural behaviour of existing structures:

• The real bearing capacity of existing structures: in order to make as much as possible use of the residual bearing capacity of existing structures, advanced behavioural models are necessary;
• The bearing capacity of structures with components damaged due to deterioration;
• The bearing capacity of structures designed on the basis of old codes or recommendations, not anymore meeting the actual state of the art.

A state of the art bulletin dealing with the subjects mentioned previously has recently been produced by TG 3.2. For the forthcoming period focus will be directed to aspects that have turned out to be important, but suffer from the absence of particular knowledge. This applies particularly to:

• The bearing capacity of structures with corroded reinforcement;
• Optimizing proof-loading procedures and interpretation of the results;
• Optimum use of the Levels of Approximation approach when assessing structural safety, serviceability and remaining service life.

Convener
Dario Coronelli

Co-Convener
Kamyab Zandi

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TG3.3 - Existing Concrete Structures: Life Management, Testing and Structural Health Monitoring

The Task Group 3.3 (TG 3.3) specifies and extends their focus in the framework of Non-Destructive-Testing (NDT) and Structural Health Monitoring (SHM) required for the through-life management of existing concrete structures according to the following:

• Concepts for extension of service life of reinforced concrete structures supported by NDT and SHM;
• Specific testing/ specific monitoring; testing/ techniques combined with autonomous robotic systems (remote monitoring systems) or based on digital images as well as innovative self-monitoring materials (repair, strengthening);
• Monitoring of site-specific load actions (e.g. traffic loads, etc.);
• Data management for reinforced concrete structures using NDT/SHM: data reporting and data analysis of NDT/SHM applying AI;
• Reliability assessment of NDT/SHM methods applied on reinforced concrete;
• Building Information Modelling (BIM) and Digital Twins (DT) for existing concrete structures as a decision-making tool using NDT/SHM data; implementation of SHM in BIM;
• Decision-making on structural level to foster the transformation from periodic to predictive/preventive maintenance including the assessment on the environmental impact of the decision: How can NDT/SHM contribute to operate our infrastructure in the most sustainable way?
• SHM guidelines for newly designed complex concrete structures concerning their exploitation phase, also including BIM and DT.

Convener
Sylvia Kessler

Co-Convener
Maria Pina Limongelli

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TG3.4 - Selection and implementation of interventions/through-life management activities and measures for concrete structures

The focus is on the selection and implementation of interventions and through-life management activities and measures for concrete structures.

The following aspects related to the intervention are addressed:

• Definition of intervention
• Types of intervention methods
• Selection method for intervention
• Information needed for design/execution of intervention and method for collecting information
• Materials for intervention
• Design method for intervention
• Execution method for intervention
• Assessment of performance after the intervention
• Maintenance and re-intervention of structures after intervention
• Sustainability aspects of interventions

Convener
Tamon Ueda

Co-Convener
Giuseppe Mancini

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TG3.5 - Forensic engineering

We have an enormous and an ever-increasing heritage of reinforced and prestressed concrete structures, many of which are currently approaching the end of their intended service life. However, there are pressing societal, economic and environmental needs to safely extend the service lives of many of these structures. This poses a delicate and challenging task if we are to make appropriate decisions on the through-life management and care of these constructed assets to achieve this while avoiding transferring an excessive burden onto the next generation. To do this we need a better understanding of the real behaviours of structures, why they may not achieved the required performance and, ultimately, what may cause them to fail.

Scope:

• To advance the use of techniques, processes and procedures employed in forensic engineering studies and to undertake forensic investigations – the scientific and engineering process.
• Examine how forensic engineering studies can provide improved understanding of the performance and behaviours of constructed assets (i.e. the lessons learned), with the goals of formulating improved models, identifying deficiencies / limitations and desired improvements in professional practice, etc including (amongst others) those concerned with:
• Structural safety and performance
• The economic aspects of performance / through-life cost (potentially in conjunction with TG8.4)
• Post-fire assessment of existing buildings (in conjunction with TG2)
• Durability aspects (in conjunction with COM8)
• To facilitate feedback from the understanding gained from forensic engineering studies into professional practice to improve the through-life performance of structures and buildings, such as the achievement of performance requirements, durability etc. This would include liaison and feedback as appropriate to fib Commissions and other collaborating bodies.
• Investigate how the provisions of fib MC2020 / the fib Model Code for Concrete Structures facilitate forensic investigations and the benefits arising thereof.
• To advise what changes / additions are required in future editions of the fib Model Code for Concrete Structures from the understanding gained from forensic engineering studies and to facilitate the application of forensic engineering / forensic investigations of structural condition and performance.
• To work with other fib Commissions / other bodies as appropriate

Convener
Daniele Zonta

Co-Convener
Frank Papworth

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