PSI - Issue 84

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

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scenarios considered in the previous study are therefore adopted. The numerical model represents the thermo-physical behaviour of a lightweight gypsum-based sprayed plaster and was calibrated through comparison between experimental and numerical heating curves. Experimental data were obtained from cone calorimeter tests on bare and protected steel plates, while numerical simulations were carried out using SAFIR under equivalent boundary conditions. Model calibration was achieved by adjusting the main heat transfer parameters, including thermal conductivity, specific heat, dry density, and moisture content, see Table 1. The calibrated model was then applied to the steel–concrete composite bridge, allowing realistic simulation of protected configurations with different coating thicknesses (10, 14, 20, and 30 mm).

Table 1. Input physical and thermal properties of protective material in the numerical model.

c [J/kgK]

 dry [kg/m

3 ]

w [kg/m 3 ]

 start [°C]

 end [°C]

h c [W/m

2 K]

 [-] 0.65

1000

423

210

100

105

25

3.2. Preliminary Life cycle costs results The initial cost of the bridge includes the baseline construction cost and the additional cost of the passive fire protection , with = + . For the typological SCC bridge, the preliminary results are shown in Table 2. Table 2. Initial costs of bridge for the analysed configurations. Configuration C C * [k€] C P [k€] C I =Cc*+C P [k€] unprotected 223.44 - 223.44 protected with SFRM 10 mm 223.44 3.56 227.00 protected with SFRM 14 mm 223.44 3.56 227.00 protected with SFRM 20 mm 223.44 7.12 230.56 protected with SFRM 30 mm 223.44 10.68 234.12 Maintenance costs , accounting for both structural elements and fire protection over a 100-year service life with a 3% discount rate, are calculated as 2% of the initial cost per year. Direct losses are estimated using fragility curves and the replacement costs of critical structural components, with repair costs defined according to performance levels (100% for severe damage and 50% for moderate damage). Indirect losses, reflecting socio-economic impacts due to service disruption, are evaluated using local-scale parameters. 4. Preliminary results Thermal analyses were performed on all structural components using the SAFIR software, considering a total simulation time of 36 hours, in order to allow the structure to cool down to ambient conditions after fire extinction, making it possible to investigate thermal effects both during and after the fire event, including the assessment of post fire operability in terms of residual deformations. The comparison between unprotected and protected bridge configurations reveals marked differences in temperature evolution and overall thermal behaviour of the structural elements. The results clearly demonstrate the ability of passive fire protection systems to delay and reduce heat transfer to the steel components. In the absence of protection, steel members experience a rapid temperature increase during the early stages of fire exposure. Conversely, the presence of passive protection leads to a substantial reduction in thermal demand on the steel elements, as illustrated in Fig. 1. Numerical simulations carried out for different protection thicknesses (10, 14, 20, and 30 mm) show a clear decrease in steel temperatures with increasing insulation thickness, confirming the effectiveness of the protective layer in mitigating fire-induced thermal actions.