Eduardo S. Cavaco

Robustness of corroded reinforced concrete structures – a structural performance approach

The aim of this work is to provide new contributions in order to define more accurately the structural robustness concept, particularly when applied to corroded reinforced concrete (RC) structures. To fulfil such a task, several robustness indicators are analysed and discussed with special emphasis on structural-performance-based measures. A new robustness definition and a framework are then proposed for its analysis, based on the structural performance lost after damage occurrence. The competence of the proposed methodology is then tested comparing the robustness of two RC foot bridges under corrosion. The damage considered is the longitudinal reinforcement corrosion level, and load carrying capacity is the structural performance evaluated. In order to analyse corrosion effects, a finite element (FE) based on a two-step analysis is adopted. In the first step, a cross-section analysis is performed to capture phenomenons such as expansion of the reinforcement due to the corrosion products accumulation; damage and cracking in the reinforcement surrounding concrete; steel–concrete bond strength degradation; effective reinforcement area reduction. The results obtained are then used to build a 2D structural model, in order to assess the maximum load carrying capacity of the corroded structure. For each foot bridge, robustness is assessed using the proposed methodology.

On the robustness to corrosion in the life cycle assessment of an existing reinforced concrete bridge

Abstract Management of existing structures has traditionally been based on condition assessment, based on visual inspections, disregarding the susceptibility of different structural types to aging and deterioration. Robustness, as a measure of the effects of unpredictable damage to structural safety can be a complementary information to the results of inspection. Although robustness has mostly been used to evaluate the consequences of extreme events, a similar framework can be used to investigate the result of aging, allowing a better understanding of the potential effects of deterioration and allowing a better allocation of available maintenance funding. In this work, a probabilistic structural robustness indicator is used to quantify the susceptibility of structures to corrosion. The methodology is exemplified through a case study comprising an existing reinforced concrete bridge deck, heavily damaged due to reinforcement corrosion, and finally demolished due to safety concerns. Robustness measures the bridge deck safety tolerance to reinforcement corrosion. The principal effects of corrosion, including loss of area and bond between concrete and steel are modelled using a non-linear finite-element model, coupled with a Response Surface Method to compute the bridge reliability as a function of the corrosion level, and finally used to assess robustness. Results show that the redundancy of the bridge allows significant redistribution of loads between elements with different corrosion levels. As a result, the bridge presents significant robustness and tolerance to reinforcement corrosion.

Life-cycle system performance of bridges: a robustness-based approach

Corrosion in reinforced concrete and steel structures is among the most damaging phenomena to structural safety and therefore one of the most demanding when facing the life-cycle analysis of such structures. However, the onset and progression of corrosion is highly uncertain. Because damage due to corrosion appears due to environmental aggressive agents which progress on time, it is of interest to develop suitable life-cycle measures of structural robustness with respect to a progressive deterioration of the structural system performance. In this paper, a robustness-based approach as presented in Cavaco et al. (2013) is used to quantify the effect of corrosion on safety and life-cycle maintenance. The level of corrosion is considered as an uncertain parameter. In this way, a probabilistic measure of the robustness, seen as the tolerance to damage, can provide a comprehensive description of the life-cycle system performance. Therefore, a robustness definition and the calculation of the corresponding robustness index are proposed in the paper and further applied to one reinforced concrete and one steel existing bridge to show the practical application and results when applied to real bridges. It is shown how the obtained robustness index for the bridges can be directly co-related to their life-cycle performance and also used to define the optimum intervention strategies.