Composite slabs with steel deck combine the load-bearing resistance of the steel deck and
rebar with the compressive resistance of the concrete (components). Unprotected composite slabs
may be exposed to natural fire conditions from below, and steel reduces its load-bearing capacity
during the heating stage. In short fire events, with limited deformations, the composite slabs can
recover the load-bearing capacity during the cooling stage. This research presents the validation of
the numerical model and the development of a parametric study, to evaluate the load-bearing
capacity during the fire event. This method includes a time step procedure, based on the average
temperature calculation for each component, including the reduction coefficients applied to the
design strength of each material. A new proposal is also presented to evaluate the residual loadbearing
capacity. In some circumstances, the residual load-bearing can be reduced by more than 20%.
The results showed that the highest variation in the load-bearing resistance of composite slabs occurs
when the steel temperatures are between 20 and 600 ℃, after this temperature, the steel has already
lost most of its mechanical strength. Moreover, it was observed that different heating rates and
different cooling rates influence the rate of the reduction and recovery of the load-bearing capacity. It
was also noticed that the lowest load-bearing capacity of the composite slabs was reached after the
end of the heating phase, showing that the stability of the element during the heating phase does not
guarantee fire safety during the cooling phase.
