Tensile membrane action of RC slabs and steel-concrete composite slabs at elevated temperatures

Slabs can take full advantage of tensile membrane action (TMA) in fire conditions to improve the ultimate bearing capacity. This paper proposed a novel analytical method to determine the ultimate bearing capacity of both reinforced concrete slabs and composite slabs at elevated temperatures, considering the influence of TMA. In this analytical model, a well-defined equation for the elliptical boundary of the TMA region is reasonably determined, and the enhancement of TMA is derived from a series of force and moment equilibria. The analytical method shows a good agreement with the test results. The analytical analysis reveals that while increasing temperature has little effect on the geometry of the membrane action region, it significantly influences the enhancement of ultimate load due to the temperature-induced stress redistribution in the slab. In addition, the membrane action predicted by the analytical method aligns well with that predicted by the numerical method. The development of TMA progresses from the boundary of ellipse to centre, according to the stress distribution predicted by numerical analysis. Finally, with the aid of test results and numerical results, span/10 and span/8 are suggested as the failure criteria for reinforced concrete slabs and steel-concrete composite slabs in fire conditions, respectively.