PSI - Issue 44

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Gianfranco De Matteis et al. / Structural Integrity Procedia 00 (2022) 000–000

682 © 2022 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license ( https://creativecommons.org/licenses/by-nc-nd/4.0 ) Peer-review under responsibility of the scientific committee of the XIX ANIDIS Conference, Seismic Engineering in Italy Keywords: Material testing; Benchmark; Collapse probability; Numerical modelling Gianfranco De Matteis et al. / Procedia Structural Integrity 44 (2023) 681–688

1. Introduction Bridges are critical parts of railway and road networks worldwide. Most of them are nowadays made of reinforced concrete and were built in the second part of the last century. After almost one century of use, many bridges show signs of ageing due to external actions, aggressive environment, degradation of materials and anthropic activities. For this reason, a significant amount of research in civil engineering is now concerned with the diagnosis, assessment, monitoring and retrofitting of existing reinforced concrete bridges (D'Amato & De Matteis, 2022). To date, several methods are available in the literature for evaluating the performance of bridges against traffic and seismic loads, with different refinement levels. For instance, in the recent Italian “Guidelines for classification and risk management of existing bridges” (MIT, 2020) a multi-level approach is adopted, consisting of a census, a visual inspection for ranking a global defect level and, if required, also numerical simulations for the safety assessment. As far as numerical models are concerned, EuroCode 2 (EN 1992-2, 2006) proposes a specific method for evaluating the structural performance of new RC bridges by means of Nonlinear Analysis (NLA). The method is based on a specific Safety-Format (SF), which in general may be identified by the following characteristics: • the values of geometric and material properties to be used for NLA, affecting both structural strength and relative failure mode (Cervenka, 2008); • when to stop the NLA incremental process; • how to derive the “ultimate failure load” that can be carried by the structure within the safety margins required by the semi-probabilistic method. According to the EC2 method, the mechanical behaviour of the structure is simulated by a numerical model in which nonlinear stress-strain relationships are defined starting from the mean values of material strengths. The loads are applied following an incremental path until global failure is reached, and the safety check is carried out on the overall structure through the use of a Global Resistance Format (GRF) (fib, 2012). This implies the verification of one of the following inequalities: � + � ≤ � � � + � ≤ � ⋅ � = � ′ � � + � ≤ � � (1a) (1b) (1c) where γ Rd = 1.06 is the partial factor for model uncertainty for resistance, γ Sd = 1.15 is the partial factor for model uncertainty for action, γ O = 1.20 is the overall safety factor, and γ O’ = γ Rd · γ O = 1.27. In Eq. (1), q ud represents the ultimate loading obtained by NLA. It should be remarked that the previous inequalities permit to check the safety (also indicated as global resistance) at a global level instead of at each section, as in the case of linear structural verifications. Of course, this approach is capable of accounting for all the nonlinearity sources of a structure, requiring, on the other hand, more efforts and time in performing the analyses with respect to a linear model. Moreover, in the last years huge efforts in research have been exploited and several improvements to the SFs for NLA of RC structures have been performed to overcome the limits of EC2 approach (Castaldo, et al., 2019; Tur, et al., 2020). Starting from these premises, in this paper the use of NLA and SF proposed by the EC2 is extended to existing RC bridges, highlighting the main critical issues to be addressed for its application. At first, the main aspects regarding the adopted SF format are introduced and commented. Then, an application to a case study is presented, comparing results of NLA with those derived from linear analyses characterised by different levels of modelling accuracy. The use of NLA for the structural assessment of existing bridges is not explicitly accounted for by the code. This paper hence investigates the use of NLA in the safety assessment of existing bridges, highlighting critical conceptual and practical aspects which need to be solved in the application.