A reliability-based measure of robustness for concrete structures subjected to corrosion

This work is a contribution to the definition and assessment of structural robustness. Special emphasis is given to reliability of reinforced concrete structures under corrosion of longitudinal reinforcement. On this communication several authors’ proposals in order to define and measure structural robustness are analyzed and discussed. The probabilistic based robustness index is defined, considering the reliability index decreasing for all possible damage levels. Damage is considered as the corrosion level of the longitudinal reinforcement in terms of rebar weight loss. Damage produces changes in both cross-sectional area of rebar and bond strength. The proposed methodology is illustrated by means of an application example. In order to consider the impact of reinforcement corrosion on failure probability growth, an advanced methodology based on the strong discontinuities approach and an isotropic continuum damage model for concrete is adopted. The methodology consist on a two-step analysis: on the first step an analysis of the cross section is performed in order to capture phenomena such as expansion of the reinforcement due to the corrosion products accumulation and damage and cracking in the reinforcement surrounding concrete; on the second step a 2D deteriorated structural model is built with the results obtained on the first step of the analysis. The referred methodology combined with a Monte Carlo simulation is then used to compute the failure probability and the reliability index of the structure for different corrosion levels. Finally, structural robustness is assessed using the proposed probabilistic index. reached about its definition and the framework to assess it. In fact there are also some robustness related concepts, such as vulnerability, redundancy and ductility, among others, that are frequently misunderstood. In the last two decades several authors appeared with different robustness approaches (Frangopol and Curley 1987, Lind 1995, Goshn and Moses 1998, Biondini and Restelli 2008, Baker et al. 2008, Starossek and Haberland 2008, Cavaco et al. 2010). Among the proposals, some are deterministic based and other are probabilistic based. Another point of interest is the fact that some authors support the idea that robustness is an intrinsic structural property depending on the structural ability to maintain an adequate performance level after damage occurrence. The works of Frangopol and Curley (1987), Lind (1995), Biondini and Restelli (2008), Starossek and Haberland (2008) and Cavaco et al. (2010) follow this perspective. On the other hand, other authors (Goshn and Moses 1998 and Baker et al. 2008) prefer to consider robustness as a property of the structure and its environment. In this case robustness is related with the magnitude of the damage trigger event and the consequences extent. At the same time this robustness perspective is much broader since to compute the consequences of structural failure it is necessary to have in consideration all the social and economic environment aspects. Therefore, in this case robustness supersedes the structural engineer domain. In Figure 1 the different proposals for the robustness concept and the framework to assess it are presented and organized accordingly to the perspective assumed by the respective author.