On the interaction between span length and opening ratio of RC frames under natural fires

Three reinforced concrete (RC) structures of the same height (3000 mm) but with different span lengths (4500, 6000 and 7500 mm) were subjected to nine different natural fire curves when different opening ratios (0·02–0·20) were applied. All the cases aimed to meet a 60 min fire resistance rating (FRR) based on the standard ISO 834 fire curve. Structural fire analyses showed that there was no collapse during the heating phase, confirming that all the cases were able to meet the required FRR. However, the results also showed that the possibility of structural failure during the decay phase increased with increases in span length and opening ratio. Furthermore, the results showed that structures with larger span lengths were more susceptible to collapse during the cooling phase than structures with shorter span lengths. The results of this study can be used as guidance to determine the FRR of structures with different opening ratios, thus providing more information about structural performance prior to a fire event.