PSI - Issue 64

Donatella de Silva et al. / Procedia Structural Integrity 64 (2024) 1806–1814 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Figure 9. Fragility curves for performance level III and performance level IV: a) maximum displacement; b) residual displacement

Figure 10. Fragility curves for performance level III and performance level IV: a) maximum displacement; b) residual displacement

To enhance the fire resistance of composite steel-concrete bridges, several strategies can be recommended. Applying fire-resistant materials, such as intumescent or spray-on fire-resistive materials to steel elements can significantly improve fire performance, as these materials with their low thermal conductivity, provide an insulating layer. Increasing the concrete cover over steel reinforcements is another effective method, as it enhances thermal resistance. 7. Conclusions This study contributes to increasing knowledge for the design or verification of bridges under fire conditions. The principal conclusions that emerge from this study are: • in the absence of code, the analysis of fire conditions is fundamental for transportation infrastructures; • the choice of vehicle or combination of vehicles involved in the fire is crucial for the magnitude of the effects produced on the structures; • the composite bridge, with steel beams directly exposed to the fire, was found to be more vulnerable than the prestressed reinforced concrete bridge; • the determined fragility curves can be used both in the design phase and in the verification phase of existing structures, and potentially for designing improvement interventions. To improve the fire resistance of these bridges, some passive protection strategies can be adopted and evaluated with the same methodology proposed in this work, to measure the structural fire vulnerability reduction. Furthermore, among the future developments of this work, the effect of these protections could be quantified, also by adopting a cost-benefit analysis. In conclusion, the proposed methodology constitutes an operational tool for engineers to assess the fire resistance of this type of structures. Indeed, after the selection of fire scenarios in terms of fire load and HRR curve, the designer can understand the vulnerability of the analyzed bridge by entering in the fire fragility curves. Acknowledgements