Progressive collapse of multi-storey buildings due to sudden column loss—Part II: Application

Abstract

The companion paper presents the principles of a new design-oriented methodology for progressive collapse assessment of multi-storey buildings. The proposed procedure, which can be implemented at various levels of structural idealisation, determines ductility demand and supply in assessing the potential for progressive collapse initiated by instantaneous loss of a vertical support member. This paper demonstrates the applicability of the proposed approach by means of a case study, which considers sudden removal of a ground floor column in a typical steel-framed composite building. In line with current progressive collapse guidelines for buildings with a relatively simple and repetitive layout, the two principal scenarios investigated include removal of a peripheral column and a corner column. The study shows that such structures can be prone to progressive collapse, especially due to failure of the internal secondary beam support joints to safely transfer the gravity loads to the surrounding undamaged members if a flexible fin plate joint detail is employed. The provision of additional reinforcement in the slab over the hogging moment regions can generally have a beneficial effect on both the dynamic load carrying and deformation capacities. The response can be further improved if axial restraint provided by the adjacent structure can be relied upon. The study also highlights the inability of bare-steel beams to survive column removal despite satisfaction of the code prescribed structural integrity provisions. This demonstrates that tying force requirements alone cannot always guarantee structural robustness without explicit consideration of ductility demand/supply in the support joints of the affected members, as determined by their nonlinear dynamic response. Keywords IntroductionA new relatively simple yet sufficiently accurate methodology is presented in the companion paper [1] , which aims at appraising the efficacy of multi-storey buildings to resist progressive collapse triggered by sudden local column failure, as a consequence of an extreme loading event. The potential for progressive collapse is assessed in three independent stages based on the ductility demand and supply in the critical regions of the affected structural members. A significant advantage of the developed procedure is that it can explicitly account for the dynamic effects associated with the instantaneous column removal through a simplified energy equivalence approach, thus avoiding the need for nonlinear dynamic analysis. With respect to its applicability, the proposed method accommodates both simplified and detailed models of the nonlinear static response. Moreover, it can be implemented at various levels of structural idealisation, depending on the required level of sophistication, the feasibility of model reduction and the availability of analytical tools [1] . These levels correspond to either the full structure, excluding the damaged column, or critical sub-structures in which ductility demands are concentrated.The componen...

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

“…The magnitude of these demands, which are 8 generally significantly higher than those associated with a sudden column loss scenario [7,12,13] , is attributed to the significant amount of kinetic energy acquired by the upper floor immediately prior to impact. Depending on the particular characteristics of the impact event, the theoretical calculation discussed in the previous section has shown that the percentage of the imparted energy can vary from approximately 40% to nearly 100% of the initial energy for fully plastic and fully rigid impact scenarios, respectively.…”

“…Depending on the required level of sophistication and the availability of analytical tools, the static floor response can be established using either detailed or simplified modelling techniques, the relative benefits of which are discussed elsewhere [5][6][7]13] .…”

“…Hence, structural robustness is directly related to the ability of the structure to redistribute the loads and remain stable following this extreme event. The limit state that is considered in association with this design scenario is failure of the floor(s) above the removed column [5][6][7] . Nonetheless, no matter how unlikely this seems in view of the significant kinetic energy acquired by one or more falling floors following failure, it is still possible under specific circumstances for the lower part of the structure to arrest impact and prevent progressive collapse.…”

“…With particular reference to steel-framed buildings with partial-strength joints, the floor limit state is associated with failure of a single joint, which is assumed to occur when the ductility demand exceeds the ductility capacity in one or more of the joint components [6,7] .…”

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.…”