Membrane actions of RC slabs in mitigating progressive collapse of building structures

Potential for progressive collapse of RC buildings can be studied using sudden column loss scenarios. The loss of either a penultimate-internal (PI) column or a penultimate-external (PE) column is among the most critical scenarios since it leaves the associated beam-and-slab substructures laterally unrestrained. At large deformations, the membrane behaviour of the affected slabs, consisting of a peripheral compressive ring of concrete supporting tensile membrane action in the central region, represents an important line of defence against progressive collapse. In this paper, an advanced finite element model (FEM), which has been validated by available test data, is used to investigate the membrane behaviour in laterally unrestrained slabs associated with PI column loss in the presence of interior double-span beams, rotational restraints along the perimeter edges, and the slab top reinforcement. It has been shown that in the central region, greater tensile membrane forces are mobilised due to the participation of beam reinforcement and slab top reinforcement. In the outer region, the compressive ring of concrete is also strengthened by slab hogging moment. Hence, the overall load-carrying capacity of the affected structures can be enhanced significantly to sustain the gravity applied loads which are severely amplified by both double-span effect and dynamic effect.