A Simplified Approach To Assess Progressive Collapse Resistance Of Steel Framecomposite Floor Structures

Since the collapse of the World Trade Centre towers in 2001,a flurry of research studies on the structural progressive collapse performance has been stirred up within domestic and international project circle.The progressive collapse issue involves deeply into the whole architectural structure.It shall take geometric nonlinearity and material nonlinearity into account,as well as the dynamic effect due to the sudden failure of a local structural member,which make this event extremely complicated.Up to now,experimental investigation and numerical simulation are the two main research techniques.As for three-dimensional structures,experimental investigation is often enslaved to laboratory condition and research budget,whereas it's inefficiency or even beyond computation for numerical simulation due to enormous elements and a large number of interactions during overall structures.Besides,different modeling approaches will result in variant simulated results.In brief,these two methods go against direct application for civil engineers.Therefore,it's urgently needed to come up with a simplified approach to assess progressive collapse resistance of overall structures.Based on the research achievement from experimental investigation of steel frame-composite floor structures subjected to interior column loss,this paper comes up with a simplified approach for direct application for civil engineers.The main contents in this paper are summarized as follows:(1)Confirming load-transferring mechanisms at different loading stages through the discussion of structural destruction process under progressive collapse condition,which provides sound theoretical basis for the establishment of assessment approach.(2)The load-carrying capability of a structure at small deformation stage equals to the combination of the bearing capacity of slab from yield line theory and the flexural capacity of composite frames.Besides,this paper provides a simplified algorithm to calculate catenary action in beams and tensile membrane action in slabs that subjected to large deformations.(3)Proposing two simplified formulas to calculate vertical deformation values of composite frame structure at small and large deformation stages,respectively.(4)Based on the static load-displacement curve predicted by assessment approach,this paper takes the energy balance method that proposed by Izzuddin to calculate the dynamic load-carrying capability.(5)Verifying the accuracy of the proposed assessment by comparing calculated values with existing experimental and simulated results of three-demensional structures,and it is followed by two demonstrations which can be referred by civil engineers or researchers.Innovations:(1)For the first time,this paper proposes a simplified but accurate formula to calculate composite frame structures with semi-rigid connections,which can take elastic-plastic effects into account.(2)Providing a simplified algorithm to calculate catenary action in beams and tensile membrane action in slabs that subjected to large deformations for the first time.(3)For the first time,this paper proposes a simplified assessment approach to account the dynamic progressive collapse resistance of steel frame-composite floor overall structures,which can be referred by engineers.