Simulação numérica do comportamento ao fogo de estruturas mistas (lajes)

Abstract

This study investigates the thermal behaviour of composite steel and concrete slabs with profile steel deck under standard fire conditions corresponding to a fire from the bottom. This composite solution consists of a concrete topping cast on the top of a steel deck. The concrete is typically reinforced with a steel mesh and may also contain individual rebars. The deck also acts as reinforcement and may be exposed to accidental fire conditions from the bottom. This composite solution is widely used in all types of buildings and requires fire resistance in accordance to regulations and standards. Composite slabs need to meet firesafety requirements according to building codes. The fire assessment of this type of elements is normally done using standard fire tests. Two samples were tested and should take into account the criterion for stability (R), Integrity (E) and insulation (I). The fire rating for (R) and (E) is not in the scope of this investigation. The fire rating for insulation (I) is evaluated by three different methods (numerical simulation, simple calculation and experimental tests). Numerical simulation was performed using Matlab partial differential equation toolbox and by the software ANSYS, for the thermal effects of standard fire exposure. The fire rating is calculated for 196 different geometric configurations, therefore, 394 simulations were performed in order to evaluate the effect of the thickness of the concrete layer and the thickness of steel deck. The fire resistance (I) increases with the thickness of the concrete, according to the results obtained with both methods. The numerical results are also compared with the simplified method proposed in the Annex D of Eurocode 4 and the Brazilian standard NBR 14323:2013, which appears to be unsafe.