Existing structures often no longer meet the demands formulated in contemporary design codes with respect to structural safety and serviceability. This occurs, for instance, if the loads on existing structures, like traffic loads on bridges, are larger than assumed in the original design. A second potential reason is that structures are subject to deterioration, like alkali–silica reaction within the concrete or corrosion of the reinforcement due to chloride attack or carbonation. A third possible reason is that in recent codes, additional criteria have been introduced based on new theories and/or negative experiences with older structures. The new fib Model Code for Concrete Structures 2020 will be valid both for the design of new structures and the assessment of existing structures. This paper shows how the design and assessment of concrete structures are integrated into this new code concept.

For the assessment of concrete structures in the new fib Model Code 2020 (fib MC 2020), three categories are distinguished: (1) the residual capacity of existing structures without damage, (2) the residual capacity of structures suffering deterioration, and (3) the residual capacity of structures with noncompliant details. In the accompanying paper by Walraven and Dieteren in this volume, the backgrounds for this subdivision have been explained, and indications for the assessment of existing concrete structures in those categories have been given. In the actual paper, examples are given how to perform an assessment of concrete structures for the categories mentioned above. These examples have contributed to the formulations of the recommendations proposed for fib MC 2020.

Discussions have been underway in fib (Fédération Internationale du Béton) about advancing the fib Model Code for concrete structures. These include the fib international workshop in The Hague (June 2015), the fib MC2020 Core Group meeting in Madrid (December 2015), and a series of follow-up worldwide consultations on the fib ambition regarding the new developments in structural codes, including the special session on Model Code in the fib Symposium in Maastricht (June 2017). This paper discusses the main aspects of the development of fib MC2020, which is envisaged as a single-merged general code fully integrating the provisions for the design of new concrete structures with matters relating to existing concrete structure. It needs to deal effectively with both the design of structures and all the activities associated with the through-life management of existing concrete structures, including matters such as their in-service assessment and interventions upon them. To that end, MC2020 will take sustainability as a fundamental requirement, based upon a holistic treatment of societal needs and impacts, life-cycle cost and environmental impacts. This paper discusses the main aspects of the development of fib MC2020. As part of this, the envisaged contribution of fib T10.1: Model Code 2020 is reviewed. However, recognizing the overall ambition of the fib MC2020 project, it is clear that all fib commissions, along with other bodies able to make contributions on relevant topics, will need to work together to assemble the breadth of knowledge and expertise which will be required for the fib MC2020 project.