Critical issues in safety assessment of existing reinforced concrete bridges by means of nonlinear analysis

In the last decade, the Italian bridge heritage, mostly made of ordinary or pre-stressed Reinforced Concrete (RC) elements, has increasingly shown signs of ageing, testified by the recent collapses as consequences of concurrent lack of maintenance, degradation of materials, increase in vehicular traffic and exceptional actions (e.g. due to landslides and floods). The recent Italian “Guidelines for classification and risk management of existing bridges” confirm the large interest at policy-making level for accurately assessing ordinary and ultimate performance of existing bridges, through a multi-level approach. As for the numerical simulations, to date within the literature Non-Linear Analysis (NLA) methods have been proposed in the literature only for designing new RC bridges. Among the others, EuroCode 2 (EC2) proposes a specific method for simulating the structural performance of new RC bridges, based on a specific safety-format (SF), where the mean values are the representative strengths for materials. In this paper, the application of the EC2 method, proposed for new RC bridges, is critically reviewed in order to examine its applicability for to existing RC bridges. The choice use of the representative strengths is discussed, in relation to the current knowledge level achieved before the structural assessment. Estimation of modelling uncertainty is proposed as a means to define some acceptance criteria for the specific numerical solution strategy to be used, following the most recent international research outputs. Finally, the relationship between the predictions provided by nonlinear analysis and those obtained by linear methodologies at involving different levels of the modelling detail is comparatively investigated with reference to a specific case study.