PSI - Issue 78

Ataklti Gebrehiwet Gebrekidan et al. / Procedia Structural Integrity 78 (2026) 1665–1672

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1. Introduction Bridges are essential elements of transportation infrastructure; their performance under various hazards, such as earthquakes or floods, is crucial because their failure can lead to business disruptions, loss of social reputation, difficulties in rescue operations, and fatalities (Rathore and Garg, 2022). With this in mind, the seismic assessment and, if needed, retrofitting cannot be overlooked, particularly in earthquake-prone regions. Many bridges, especially those built post-WWII and before the introduction of modern seismic codes, may require upgrading (Skokandić et al., 2022). Nowadays, various interventions are available to improve the seismic performance of bridges (Stefanidou, 2023). However, when multiple retrofit options that meet code requirements are feasible, selecting the optimal strategy should be based on a multi-criteria evaluation that accounts for economic, social, technical, and environmental factors, rather than considering only direct cost comparisons (Caterino et al., 2008; Stefanidou, 2023). Various methods have been proposed or used in literature to select an optimal retrofit solution with respect to seismic actions. Some studies focused on resilience-based approaches for assessing and mitigating seismic risk of bridge structures. For example, Cimellaro (2013) introduced the concept of resilience-based design (RBD). Alternatively, Sousa and Monteiro (2018) proposed a benefit-cost ratio analysis, determined by dividing the change in expected annual loss by the total cost of the retrofit. It is however acknowledged that broader multi-criteria approaches are useful to determine the optimal solution among several alternatives, i.e. the one characterised by the highest degree of advantage with respect to all the criteria representing the decision problem (Caterino et al., 2008; Villalba et al., 2024). Such approaches can make use of a combination of structural seismic response characteristics, economic variables, social or other indicators to determine the preferable alternative from a finite set of retrofitting alternatives. Among the available MCDM-based approaches, the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) has been widely applied in seismic retrofitting selection because of its ability to handle diverse judgment criteria and provide clear results by selecting the best alternative based on the shortest distance to an ideal solution (see, e.g., Caterino et al. (2008) for the case of buildings). In turn, the Analytic Hierarchy Process (AHP) is commonly used to weight criteria through pairwise comparisons (Villalba et al., 2024). For this study, the TOPSIS approach was selected, based on its successful application in numerous previous studies evaluating retrofit alternatives based on economic, social, and environmental criteria (Caterino et al., 2008; Clemett et al., 2022). Furthermore, nowadays, environmental impacts (EIs) emerge as a crucial aspect in retrofitting decision making hence, they should be considered when making decisions that are aligned with sustainable development principles. To this end, there are various studies in literature that made use of MCDM approaches and considered environmental aspects for the identification of optimal retrofit solutions for building (Caruso et al., 2021; Clemett et al., 2022; Couto et al., 2024). Nevertheless, the role of environmental impacts in bridge seismic retrofitting selection has only been marginally investigated (Billah and Alam, 2014; Briseghella et al., 2022) with respect to buildings. Consequently, this study focuses on a multi-parameter evaluation of seismic retrofitting strategies for a three-span RC bridge at different seismic hazard levels, highlighting the role of environmental impacts, to increase sustainability. 2. Case study bridge 2.1. As-built structure and proposed retrofitting alternatives The considered case-study bridge (Figure 1) was built during the 1990s. Its as-built configuration features a steel concrete composite deck with a symmetric Gerber-type design over reinforced concrete piers, also known as the Kentucky scheme. The two piers consist of five columns each, with a diameter of 0.80 m and a height of about 6.5 m. The reinforcement consists of 12 longitudinal rebars with a diameter of 24 mm and circular hoops with a diameter of 12 mm, spaced at 150 mm. The steel reinforcement has a yield strength of 326 MPa, and the concrete compressive strength is 23 MPa. Two locations are considered to evaluate the impact of different seismic hazard levels on the case study bridge. One corresponds to the original site of the bridge, Tortona, located in northern Italy, of low seismic hazard . The other, L’Aquila , in central Italy, is characterised by high seismic hazard.