A state-of-the-art review on tensile membrane action in reinforced concrete floors exposed to fire

Significant work has been done on the enhancement of load-bearing capacity of reinforced concrete slabs through tensile membrane action (TMA) under fire conditions, since its first identification in Cardington fire tests conducted in the 1990s. This paper presents a state-of-the-art review on the corresponding experimental studies, numerical analyses, simple calculation approaches and current design methods. Experimental results demonstrate that an average enhancement up to 2.7 times the yield line capacity can be achieved, and the measured maximum deflection of slabs can reach a degree of span/10 without collapse. However, large-scale fire tests are still required to confirm the failure mode of a full-depth cracking across the short span observed in small-scale fire tests. Previous numerical analyses show that the occurrence and development of TMA significantly depend on the boundary condition, temperature distribution, reinforcement layout, bond strength and aspect ratio. Simple calculation methods can be classified into two groups: equilibrium-based and energy-based methods. They differ from the consideration of the horizontal restraint, critical reinforcement strain, bond strength, deflected shape. A comparison of predicted and measured failure deflections indicates that the ultimate strain of reinforcement should be used to allow a larger maximum deflection. A trilinear thermal gradient model is recommended, instead of existing linear and bilinear models, to additionally represent the nonlinear temperature distribution in the lower fire-exposed portion of slabs. It is suggested that the dependency of failure modes on the boundary condition, reinforcement layout, strain concentration effect and local temperature rise of reinforcement at cracks should be paid more concern.