PSI - Issue 84

Donatella de Silva et al. / Procedia Structural Integrity 84 (2026) 1353–1360

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substances have raised the probability of fire events occurring on bridge infrastructures. idents involving fuel tankers may trigger hydrocarbon fires (Battelle, 2004), which develop extremely rapidly and are associated with very high thermal loads. Such events can produce critical temperature levels within a short time, leading to severe deterioration of structural elements and, in some cases, to rapid structural failure (Naser 2015).Steel and composite steel–concrete bridges are particularly sensitive to fire effects due to the thermal properties of steel members (Saxena, 1992, Neuenschwander, 2017, Chen, 2006). The rapid heat transfer through slender sections causes a fast temperature rise, resulting in a reduction of mechanical properties and load-bearing capacity. Nevertheless, fire is still often treated as a secondary hazard in bridge engineering. This lack of attention contrasts with the evidence showing that fire-related incidents have been responsible for a significant number of bridge failures (Garlock, 2012, Lee, 2013), revealing a gap in current design approaches and regulatory provisions.The evaluation of life cycle cost assessment has bene highly discussed for buildings, for example under seismic events (Miano, 2019). The research is ongoing for bridges, especially under different hazards. The impact of bridge fires is not limited to direct repair or replacement costs. Traffic disruptions, detours, and the redistribution of flows onto alternative routes generate substantial indirect costs, including increased travel times, higher fuel consumption, and congestion effects (Naser 2015). These socio-economic consequences can persist long after the fire event and, in many cases, exceed the costs associated with structural damage alone. Historical fire-induced bridge failures have shown how prolonged service interruptions may produce significant regional or national economic impacts, emphasizing the importance of accounting for economic performance alongside structural safety (Aydin, 2012, J. Zhuang, 2017). In this context, improving fire resilience through passive fire protection systems represents a strategic measure not only for enhancing structural performance under extreme thermal conditions, but also for mitigating long-term economic losses. Although the implementation of passive protection involves additional initial investment (Zhuang, 2017, Van Coile, 2023), its effectiveness must be evaluated in terms of overall cost efficiency, considering both direct and indirect consequences over the bridge life cycle. Cost–benefit analysis provides a rational framework in which costs associated with the installation, maintenance, and potential replacement of protection systems are balanced against the expected benefits derived from risk reduction. These benefits can be quantified by linking the economic consequences of fire-induced damage and failure to the probabilities obtained from fire fragility curves, which express the likelihood of exceeding specific damage states as a function of fire intensity. By integrating cost evaluation with probabilistic vulnerability assessment, the economic convenience of alternative passive fire protection strategies can be consistently compared within a performance-based fire safety design perspective. 2. Methodology for bridge fragility cost-benefit assessment The study adopts a structured methodology aimed at supporting fire safety decision-making through the combined evaluation of structural vulnerability and economic performance. The proposed framework integrates a probabilistic fire fragility assessment with a life-cycle cost analysis, enabling a consistent comparison of alternative fire passive protection strategies. The methodology is organized into five main steps. First, representative bridge typologies are defined, and their fire performance is described through predefined performance levels associated with relevant response indicators. The second step involves the characterization of fire actions by identifying realistic fire scenarios and selecting suitable fire intensity measures. In the third step, fire fragility curves are derived using cloud-based analyses based on nonlinear thermos-mechanical simulations, in which demand-capacity ratios are statistically correlated with the selected intensity measures to estimate the probability of exceeding specified performance thresholds. The fourth step consists of a life-cycle cost analysis that accounts for construction and maintenance costs, as well as expected direct and indirect losses associated with fire damage, considering both protected and unprotected configurations. Finally, the outcomes of the probabilistic and economic assessments are integrated to identify the most efficient fire protection solution in terms of structural performance, life-cycle cost, and acceptable fire risk. The definition of performance levels for bridges under fire conditions is still not explicitly addressed by current design codes, as both Eurocode EN 1991-1-2 and the Italian Technical Fire Prevention Code are primarily focused on buildings. This represents a significant limitation, since bridges exhibit distinct structural behavior and post-fire serviceability requirements compared to building structures. To address this gap, the performance-based framework proposed by de Silva et al. 2025 is adopted. Structural performance is quantified through key performance indicators, namely the maximum vertical displacement during the heating phase (SC1) and the residual displacement after cooling