Assessment of Existing Concrete Structures

In many countries the originally devised design life of a substantial part of the existing buildings and infrastructure has been reached or will be reached soon. These structures need to be assessed. Most often, existing structures are verified using simplified procedures based on the partial factor method which is commonly applied in design of new structures. Such assessments are often conservative and may lead to expensive renovation or unnecessary replacements of structures.

Recently, the engineering practice and the research community started to acknowledge that an assessment of existing structures is fundamentally different from designing new structures. For existing structures, it pays off to consider more advanced load and capacity models, as well as the overall structural behaviour, and to align the reliability assessment of concrete structures with all the information we have.

The result of the underlying reliability considerations is a different set of load factors for assessment, as well as a philosophy of increasing levels of approximation for assessment. More advanced models are then referred to as models with higher levels of approximation. In this elective you will learn about these types of models and associated considerations.

On the one hand we have more information about an existing concrete structure than we have for a structure which is still in the design process. E.g., the structure has shown a certain capacity over its lifetime, we have more knowledge about the loading, or we have knowledge about the actual concrete strength properties. Monitoring data and results from proof test might further contribute to the knowledge of a structure. We also must deal with higher uncertainty. E.g., corrosion levels might be unknown, and the structural behaviour of structural vintage details might be hard to quantify. A proper assessment should take all this information into account.

This elective will address the following topics:

• evolution of design codes and practices,

• assessment at various levels of approximation, and the link to reliability-based safety philosophies,

• modelling of the structures with vintage detailing (nonconforming design),

• determination material properties and the deterioration condition of structures,

• methodologies to deal with involved uncertainties,

• field testing, and in particular bridge load testing,

• assessment studies under multiple hazards, such as seismic action,

• structural impact of deteriorating mechanisms,

• global structural behaviour for assessment: transverse distribution, unintended composite action, contribution of non-structural components, …

• decision-making strategies

The course material of the elective will be applicable to both concrete buildings and concrete infrastructures. Most applications will be shown for concrete bridges. Since the assessment of existing concrete structures is an active research field and since codes for existing concrete structures are far from mature, this course will be updated from year to year to follow the most recent state of the research and practice.

MUDE: The first lectures of this elective will focus on the topic of safety philosophy of existing concrete structures. The influence of various sources of uncertainty, with regard to the state of information and the degradation and deterioration, will also be discussed throughout this elective.

Ethics: A discussion on the choices of the target reliability for concrete structures at different stages, namely, design, assessment, renovation is given. It will be made clear that such choice is not based on numbers but also on the ethics considerations. The topic of decision-making strategies for the assessment of existing structures will include the ethical considerations involved with this process.

Design skills: This elective will lean on general design skills of structural engineering students, which can then be applied for the analysis of existing concrete structures.