Investigations of tensile membrane action in beam-slab systems under progressive collapse subject to different loading configurations and boundary conditions

•Beam-slab structures behaved differently under point loads and distributed loads.•Tensile membrane action was affected by rotational restraint.•Penultimate-column removal was more critical than corner-column removal.•Tensile membrane action was partially developed in corner-column scenario. Although catenary action in beams and tensile membrane action in slabs are generally believed as high-level analyses to mitigate progressive collapse in a reinforced concrete building, previous research studies did not clearly differentiate the contributions of the two mechanisms in combined three-dimensional beam-slab systems. Besides, most of the recent experimental studies on column removal scenarios focused on point load application as it is more difficult to apply the more realistic uniform distributed loads in the laboratory. In this paper, numerical analyses were first employed to investigate the combined effects of beams and slabs under both point load (idealised) and uniform distributed load (more realistic) conditions. The results show that differences between these two loading methods not only affect overall structural capacities, but also influence vertical deflections and failure modes. It is also observed that tensile membrane action in slabs was less sensitive to boundary conditions compared to catenary action in beams. Moreover, catenary action in beams which showed limited development in beam-slab structures can be conservatively neglected. Besides, under uniform distributed loading condition, scenarios with different locations of column removal were numerically investigated, showing that the loss of a penultimate column, rather than a corner column, could be the most critical case, contrary to conventional wisdom. In fact, in a corner-column removal scenario, tensile membrane action can still be partially mobilised owing to the presence of two stiff discontinuous edge beams. This phenomenon was well observed in a beam-slab test conducted in this study.