The properties of reinforcing steel must comply with the fundamental assumptions underlying structural codes of practice on which verifications of structural behaviour are based. This is of predominant importance not only for design but also for assessment, where demand of deformation capacity of Reinforced Concrete (RC) is often considered implicitly. Yet, the actual deformation capacity directly depends on the mechanical properties and condition of reinforcing steel. Experimental results indicate that corrosion significantly reduces ductility, yield strength and ultimate tensile strength of reinforcement. It is however unclear which extent of corrosion may actually lead to a decrease of ultimate strain of the reinforcing steel below the minimum requirements following from the deformation capacity demands and how to consider such situations in the assessment of structures. The majority of information about the effects of corrosion on the mechanical properties of reinforcing steel is obtained from modern, ductile steel that has been corroded under an accelerated process, rather than under a more realistic long-term exposure. Moreover, experimental studies are fragmentary in scope and therefore often do not consistently consider important aspects such as the type of reinforcement steel and the morphology of the corrosion defect. Consequently, regression models developed to capture the effect of corrosion on reduction of the material properties of reinforcing steel, which are based on the empirical results, are usually characterised by large uncertainties. Given the lack of systematic consideration of the factors governing the reduction of the mechanical properties, such models tend to oversimplify the phenomena and are only to a limited extent suitable for the assessment of the structural safety of corroded structures. In this paper, governing factors for the reduction of mechanical properties of reinforcing steel due to pitting corrosion are investigated by an analytical model, accounting for the morphology of the corrosion defect and essential steel properties. Validation of the model shows good agreement with detailed FEA and experimental data.

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When non-linear finite element analyses are used in design of new or assessment of existing concrete structures, one should account for the modelling uncertainty before conclusions are drawn based on the results. The present article describes the basis for how this topic is treated in the draft of fib Model Code 2020. There are two components of the modelling uncertainty: (i) within-model, and (ii) between-model. The within-model uncertainty was estimated from a range of series of benchmark analyses gathered from the literature. Each series was assumed analyzed in a consistent manner, termed as the solution strategy. The main result for the within-model component, is a set of prior parameters for Bayesian updating. In an application setting, the prior parameters should be updated after validating the selected solution strategy with a suite of relevant benchmark analyses, before using the mean and coefficient of variation in the Global Factor Method or calculating the modelling uncertainty factor (Formula presented.) to be used in the Partial Factors Method. Finally, results from blind-prediction competitions were studied. With the present data, it cannot be concluded that a-priori knowledge of the experimental outcome reduces the uncertainty in the prediction. Hence, there is no need for compensating for this effect by a separate partial factor.

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The assessment of service-proven quay walls subject to corrosion-induced degradation is inherently a time-dependent reliability problem. Two major challenges are the modelling of corrosion and taking into account the decrease of epistemic uncertainty throughout the quay wall's service life. The main objective of this study is to examine the probability of failure, despite successful past performance, when the quay wall is subject to corrosion and randomly imposed variable loads. The development of the annual failure rate is modelled using crude Monte Carlo and by performing a first-order system reliability analysis. The annual failure rates found for service-proven quay walls vary over time. For those with successful service histories and subject to low corrosion rates, the highest reliability indices are observed in the first year of the service life, whereas with higher corrosion rates the final year prevails. In general, it seems more practical to evaluate reliability on an annual basis rather than over longer time periods, since the latter will introduce an iterative procedure to determine the wall's remaining lifetime. The key findings of this study can be crucial for the lifetime extension of existing quay walls, and presumably also for other service-proven geotechnical structures subject to corrosion.

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General frameworks for reliability differentiation have evolved over time and are mainly developed for buildings. However, recommendations for the safety of existing quay walls are lacking. In this study, target reliability indices for assessing existing quay walls were derived by economic optimisation and by evaluating the requirements concerning human safety. In quay-wall design, some dominant stochastic design variables are largely time-independent, such as soil and material properties. The influence of time-independent variables on the evolution of the probability of failure was taken into consideration, since this affects the present value of future failure costs and the associated target reliability indices. The target reliability indices obtained for existing quay walls depend on the consequences of failure and the remaining lifetime. If the failure modes of a quay wall are governed by time-independent design parameters and the quay wall has already survived the early service period, the residual probability of failure is lower for an existing quay wall compared to a new structure. Hence, this should be considered in the determination of target reliability indices. The method to evaluate quay-wall reliability over time can also be used to assess other civil and geotechnical structures.@en

General frameworks for reliability differentiation have evolved over time and are mainly developed for new buildings. However, recommendations for existing quay walls are lacking. In this study target reliability indices for assessing existing quay walls were derived by economic optimisation and by evaluating the Life Quality Index criterion (LQI). In quay wall design, some dominant stochastic design variables are largely time-independent, such as soil and material properties. The influence of time-independent variables on the development of the probability of failure was taken into consideration in this study, because this affects the present value of future failure costs and the associated target reliability indices. The reliability indices obtained in accordance with the LQI acceptance criterion were a little lower than the target reliability indices derived by economic optimization. The target reliability indices obtained for existing quay walls depend on the consequences of failure and the remaining service life. If failure modes of a quay wall are largely time-invariant and already survived the first period of the service life, the residual probability of failure is lower for an existing quay wall compared to a new quay wall. Hence, this should be considered in the determination of target reliability indices. The method of approach to assess the development of reliability over time can also be used for evaluating target reliability indices of other civil and geotechnical structures.

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