PSI - Issue 78

Antonio Cibelli et al. / Procedia Structural Integrity 78 (2026) 1221–1228

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The plaster showed significant sensitivity to the incident heat flux, attributable both to variability in the application process and to microcracking caused by thermal deformations. As shown in Figure 2, the numerical model accurately reproduces the experimental behaviour for different section factors. In the SAFIR ® simulations, the following physical and thermal properties were adopted for the protective material: a specific heat capacity of 1000 J/kgK, a dry density of 423 kg/m³, and a water content of 210 kg/m³. Dehydration was considered to occur between 100 °C and 105 °C, while surface heat transfer was modelled with a convective coefficient of 25 W/m²K and an emissivity of 0.65. 4. Results and discussion 4.1. Thermal analyses Thermal analyses were conducted on the representative substructure for a fire duration of 60 minutes. Figure 3 shows the temperature trend at the base section of the column in scenario 16, comparing the unprotected configuration with the one protected by sprayed plaster. The results highlight the effectiveness of passive protection in limiting the heating of the steel section: while the exposed steel rapidly reaches temperatures above 700 °C, in the protected con figuration temperatures mostly remain below 3 00 °C. It can be observed how the plaster helps preserving the mechan ical integrity of the column, reducing the risk of structural failure and limiting the degradation to stiffness loss only, by keeping the temperature within acceptable ranges.

(a) unprotected column

(b) column protected with sprayed plaster Fig. 3. Thermal output related to fire scenario 16 (S-16) for bare and protected configurations.

4.2. Thermo-mechanical analyses Thermo-mechanical analyses allowed quantifying the effects induced by natural fire scenarios on steel elements, in terms of displacements and internal forces. Figure 4 compares the maximum displacement at the top of the column between the unprotected configuration and the one protected with sprayed plaster, in Scenario 16. The results highlight the crucial role of passive protection in significantly reducing deformations. Although the plaster does not completely prevent the heating of the profile from a thermal standpoint, it proves more effective in limiting the maximum dis placement compared to the unprotected configuration, thus confirming its contribution to improving the structural response in case of fire.