Most of the numerical research and experiments on composite slabs with a steel deck have been
developed to study the effect of fire during the heating phase. This manuscript aims to describe the thermal
behaviour of composite slabs when submitted to different fire scenarios, considering the heating and
cooling phase. Three-dimensional numerical models, based on finite elements, are
developed to analyse the temperatures inside the composite slab and, consequently, to estimate the fire
resistance, considering the insulation criteria (I). The numerical methods developed are validated with
experimental results available in the literature. In addition, this paper presents a parametric study of the effects
on fire resistance caused by the thickness of the concrete part of the slab as well as the natural fire scenario. The results show that, depending on the fire scenario, the fire resistance criterion can be reached
during the cooling phase, especially for the thickest composite slabs. Based on the results, new coefficients are
proposed for the original simplified model, proposed by the standard. The developed numerical models allow us to realistically simulate the thermal effects caused by a natural fire in a composite slab and the new proposal enables us to estimate the fire resistance time of composite slabs with a steel deck, even if it occurs in the cooling phase.
