PSI - Issue 78

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

1227

Fig. 4. Maximum displacement exhibited under fire scenario 16 (S-16) at the column’s head cross-section in all analysed configurations.

4.3. Fragility curves Fragility curves were derived from the results of thermo-mechanical analyses conducted for each of the 36 fire scenarios. The analyses were performed for three configurations: (i) unprotected structure, (ii) structure protected with 1 cm of sprayed plaster, and (iii) structure protected with 2 cm of sprayed plaster. For each scenario, critical values of the Demand-to-Capacity Ratio (DCR) associated with performance levels PL-III, PL-IV, and PL-V were identified. These values were used to perform a linear regression on the logarithms, in order to establish a relationship between the DCR and the fire intensity measures. Both intensity measures proved effective in accurately representing the structural response to fire. The results, shown in Figure 5, highlight a significantly higher vulnerability for the unpro tected structure. The application of passive protection using sprayed plaster substantially reduces fragility, with pro gressive improvement as the thickness increases. In particular, the configuration with 2 cm of plaster demonstrates the best performance, showing a lower probability of exceeding the performance levels as the fire intensity increases.

Fig. 5. Fragility curves of the typological steel building against natural fire in bare and protected configurations.

4.4. Cost-benefit analysis The cost-benefit analysis was conducted considering a 50-year time horizon and a 3% discount rate. The results, shown in Figure 6, indicate that for low to medium fire intensity levels, the adoption of passive protection with sprayed