Progressive collapse of multi-storey buildings due to sudden column loss — Part I: Simplified assessment framework

Abstract

This paper proposes a novel simplified framework for progressive collapse assessment of multi-storey buildings, considering sudden column loss as a design scenario. The proposed framework offers a practical means for assessing structural robustness at various levels of structural idealisation, and importantly it takes the debate on the factors influencing robustness away from the generalities towards the quantifiable. A major feature of the new approach is its ability to accommodate simplified as well as detailed models of the nonlinear structural response, with the additional benefit of allowing incremental assessment over successive levels of structural idealisation. Three main stages are utilised in the proposed assessment framework, including the determination of the nonlinear static response, dynamic assessment using a novel simplified approach, and ductility assessment. The conceptual clarity of the proposed framework sheds considerable light on the adequacy of commonly advocated measures and indicators of structural robustness, culminating in the proposal of a single rational measure of robustness that is applicable to building structures subject to sudden column loss. The companion paper details the application of the new approach to progressive collapse assessment of real steel-framed composite multi-storey buildings, making in the process important conclusions on the inherent robustness of such structures and the adequacy of current design provisions.

Progressive collapse analysis of steel structures under fire conditions

“…Izzuddin et al [26,27] investigated the progressive collapse of multi-storey composite buildings modelled by a two-dimensional model. Liew [28] built a mix-element model to study three dimensional steel frames subject to blast load and fire attack.…”

Progressive collapse of multi-storey buildings due to failed floor impact

“…(14) may be used to determine the level of the suddenly applied gravity loading P' n that results in a particular maximum dynamic displacement u' d,n of the impacted floor system. Besides, similar to the case of structural systems subject to sudden column loss scenarios [5,6,13] , the overall maximum nonlinear impact response of the floor system under consideration may be expressed in terms of a P'-u' d curve, which, as illustrated in Fig. 3c, can be created by plotting the suddenly applied gravity loading P' n at each load level n versus the corresponding maximum dynamic displacement u' d,n .…”

“…3c, can be created by plotting the suddenly applied gravity loading P' n at each load level n versus the corresponding maximum dynamic displacement u' d,n . To distinguish this response from the pseudo-static response defined with reference to instantaneous column removal [5,6,13] , the term modified pseudo-static response is used in the current context, since it also accounts for the additional energy introduced into the system due to impact. Thus, based on the magnitude of the gravity loads sustained by the upper floor before failure, taken as a proportion of the initial lower floor loads P o , the maximum dynamic deformation of the impacted floor system can be obtained directly from the modified pseudo-static response.…”

Enhanced external progressive collapse mitigation scheme for RC structures

“…However, the model can become sophisticated and time consuming when the whole building is considered. Alternatively, assessment procedures involved in sudden column loss design scenarios use the nonlinear static response of the impacted floor along with an energy balance approach to estimate the maximum dynamic deformation demands without the need for detailed nonlinear dynamic analysis (Izzuddin et al, 2007a(Izzuddin et al, , 2007bVlassis et al, 2007). Focusing on steel-framed buildings with partial-strength joints, the overall ability of the floor system to arrest the impact of the above floor, and thus to prevent progressive collapse, is determined through a comparison between the ductility demands induced by the impact and the ductility capacities of the joints within the affected floor.…”