Parameters affecting tensile membrane action of reinforced concrete floors subjected to elevated temperatures

Abstract

This paper numerically investigates the mechanism and influencing factors of the tensile membrane action (TMA) developed in reinforced concrete slabs at large displacements and elevated temperatures. Explicit dynamic analyses are performed using LS-DYNA. The numerical model is first validated against ambient and fire tests on simply supported slabs. It shows that the slab responses are not sensitive to the mesh size. It is found that the 30min of heating in a standard fire can be scaled down to 1 s of computing time. Parametric studies are followed to demonstrate the influence of load ratio, boundary condition, slab thickness, reinforcement layout and aspect ratio on the occurrence and development of TMA. Five failure modes of slabs, initiated by the rupture of reinforcement, are found depending on the boundary condition, reinforcement layout and aspect ratio. As the aspect ratio increases, the location of the reinforcement rupture moves from the slab center to the intersections of longitudinal and diagonal yield lines, and further extends to the corners. For the presence of horizontal restraint at perimeter, the rupture of reinforcement occurs at the longer edges of slabs. Slabs with more reinforcement placed along the long span may fail by the rupture of reinforcement along the short span at the center of the slab. The reinforcement along the short span plays a key role in the load-bearing capacity of rectangular slabs. It is found that reinforced concrete slabs may have a fire resistance of 2 h at least due to the enhancement of TMA. The critical reinforcement temperature of 600 °C is necessary to ensure the efficiency of TMA. The deflection limit of span/20 reasonably predict the failure of slabs although a slab can resist loads at a deflection up to span/12 without collapse by means of TMA. It is recommended to increase the reinforcement ratio to enhance the effect of TMA.