PSI - Issue 84

948 Fabio Mazza et al. / Procedia Structural Integrity 84 (2026) 944–951 The common cause of fire is the ignition of highly flammable fuels due to vehicle-bridge and multiple-vehicle collisions, represented by the corresponding simple (SVi, i=1,7) and complex (SVijhk, i,j,h,k ∈ {1, . .6} ) heat release rate (HRR) curves reported, respectively, in Figs. 4a and 4b (Chen et al., 2005; Lecocq et al. 2012; Wright et al., 2013). In all the examined scenarios, the most critical position of the vehicles is considered for thermal analysis of the bridge (Fig. 3b): i.e. location A, at the center of the bridge, both longitudinally and transversely for the composite deck; location B, adjacent to the RC pier and transversely centred, for the HDRBs. The natural time-temperature fire curves are numerically simulated using the two-fire zone model adopted in the C-Fast software (Peacock et al., 2008), at A (Fig. 5a) and B (Fig. 5b) fire locations in the central span. In detail, the thermocouples are located at the bottom edge of the PC beam (Fig. 3a), assuming as input data dimensions of the fire compartment (i.e. 25m×13m×7.7m), with free lateral ventilation and two closed faces (i.e. ceiling and floor), and experimental HRR curve.

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Fig. 4. Heat release rate (HRR) curves.

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Fig. 5. Time-temperature curves.

4. Numerical results Sixty-two fire scenarios are assumed, on the assumption that all vehicles involved in the crash ignite simultaneously and linear combination of the simple HRR curves is considered. Once the natural time-temperature curve of the fire compartment is determined, it becomes possible to evaluate the temperature distribution in the most stressed structural elements by means of the SAFIR software (Gernay and Franssen, 2017). Specifically, triangular linear heat transfer elements are used in the thermal analysis of PC-RC beams, supposing that the temperature does not change along the longitudinal axis and considering a duration of the thermal analysis equal to 21600 s. Thermal conductivity and specific heat of prestressing steel and concrete vary with fire temperature according to Eurocode 2 (EC2, 2004), while other mechanical properties are assumed constant during thermal analysis: i.e. coefficient of convection on heated