Applied decision-making in civil engineering

Civil engineering facilities constitute a crucial backbone of any society and represent a considerable part of its asset. These facilities allow us to undertake activities, such as the production and transport of energy, they provide space for living or business activities or they allow for the transportation of persons and goods by private and public transportation. Civil engineering is concerned with the optimal management of civil engineering facilities. This not only comprises the design and construction of such facilities. They also have to be operated, maintained, inspected and, if necessary, repaired and/ or decommissioned. Given a specific budget, civil engineers aim to maximize the utility of these facilities. Finally, this involves engineering decision-making throughout the life cycle of such facilities. To start with, decision theory is reviewed regarding its applicability in civil engineering. For engineering decision-making, Bayesian decision theory combined with methods of structural reliability provides a consistent and applicable basis for the optimal management of civil engineering facilities. Besides probabilities, consequences need to be assessed for decision-making. A framework for their consistent consideration is introduced. It also accounts for socioeconomic consequences which often are referred to as indirect or follow-up consequences. As an example, consequences due to business interruption are reviewed. It is found that the consideration of follow-up consequences can be crucial for the identification of the optimal decision. Several approaches aim to optimize the utility of civil engineering facilities. The most general approach maximizes the expected life cycle benefit. It is shown that the minimization of the expected life cycle costs is equivalent to this approach, if the expected revenue is independent of the decision/ design variable. Moreover, it is shown that within the life cycle modeling it is possible to consider whether failed structures are reconstructed or not. Also the effect of deterioration processes can be taken into account. This includes both, the effect of the deterioration process on inspection results and secondly on the residual structural resistance. Acceptability of decision alternatives can be assessed on the basis of the life quality index (LQI). The LQI is a compound social indicator from which acceptance criteria in terms of life saving costs can be derived. The latter can be introduced into the above mentioned optimization problem. In the present work the LQI is reviewed on the basis of microeconomics consumption theory. On that basis, a simple framework is introduced, which allows to interpret a correlation that is observed between the life expectancy and the gross domestic product per capita, as the result of rational decision-making with regard to risk to life. Finally, it is shown that the described decision framework provides a basis for the calibration of modern structural design codes. Moreover, principal studies show the applicability of decision theory in civil engineering, e.g. the optimal design of different types of structures.