Membrane actions in RC beam-slab structures subjected to a penultimate-external column loss

Abstract

Progressive collapse is a commonly used term describing a disproportionate total damage with respect to the original cause. This condition happens whereby one of key structural elements is severely damaged, followed by subsequent failures of adjoining members, leading to extensive partial or total collapse of a building. The potential of progressive collapse can be investigated by using column loss scenarios in which bending moment along the beams and slabs bridging over the removed column may boost up to eight times due to doubling-of-span effect as well as amplification of gravity loads by a dynamic factor up to two. In such a case, those structural elements are overloaded beyond their capacity and are on the verge of failures unless they can find alternative load paths to sustain the amplified gravity loads. The loss of a penultimate column is found to be the most critical scenario since the associated beam-slab structures are left with a horizontally unrestrained boundary condition. At large deformations, fortunately, the beam-slab structures are able to form membrane actions consisting primarily of a peripheral compressive ring that is able to support catenary action in the slab central region, thus enhancing the overall load-carrying capacity and mitigating progressive collapse.