Study On Progressive Collapse Of Concrete-filled Square Steel Tube Columns And Composite Beams Frames

Concrete filled square steel tubular column-composite beams(CFSTCB)frame,a typical steel-concrete composite structure,has the advantages of high bearing capacity,good seismic performance,good ductility,and easy to construction,which is widely used in high-rise buildings in recent years.Although research on seismic behavior and fire resistance of high-rise buildings is a hot issue in engineering field,the progressive collapse resistance of high-rise buildings is less studied,and the research on progressive collapse resistance of CFSTCB frame is even less.By combining the research methods of theoretical analysis,experimental investigation,and numerical simulation,through examining the mechanical characteristics,resistance mechanism under progressive collapse case,and failure mode of the frames,this dissertation made intensive studies on behavior of CFSTCB frame against progressive collapse and arrived at the following conclusions:Based on single degree of freedom(SDOF)system,this dissertation investigated dynamic property of frames under progressive collapse case,discussed the relationship between initial damage time of components and dynamic loading,inspected potential and deformation energy in critical state of structural collapse,and obtained the minimum energy requirement of structural progressive collapse resistance.Collapse stages of frame progressive collapse were defined according to the development of plastic hinges along beam and sectional stress.Meanwhile,this research presented the energy and strain determination criteria on progressive collapse of frames.In order to understand the contribution and mechanism of the concrete floor in resisting the progressive collapse of the structures,analysis models for CFSTCB frame and concrete filled square steel tubular column-steel beams(CFSTSB)frame under the collapse condition were established,Stage,failure mode,stress mechanism and analysis of resistance mechanism.This dissertation inspected collapse stages,failure modes,force mechanisms,and resistance mechanisms of the frames,examined influences factors against progressive collapse of frames such as the constraint effects of concrete filled square steel tubular columns,the extensions of plastic zone in steel beam sections,bond-slip effects between steel beam and concrete wing in composite beams,and development of concrete wing cracks,and finally deduced the formulae for the resistance-deformation calculation of CFSTCB and CFSTSB frames under progressive collapse conditions.Based on the static loading tests of CFSTCB and CFSTSB frames with displacement control loading method,this research investigated the collapse stages,force transmission mechanisms,resistance mechanisms and failure modes of frames under collapsed conditions,calibrated the collapse resistance formulae proposed by the theoretical analysis.The results showed that the connections with sufficient bearing capacity and rotation capability guaranteed the resistance mechanisms against progressive collapse of frames and improved frames resistance against progressive collapse,and the concrete wing plate played a certain role in the progressive collapse process,whose contribution against progressive collapse should not be ignored in actual constructionsBased on the finite element software OpenSees and SAP2000,the concentrated plastic hinge model,the fiber element model,and the simplified multi-scale model combining the macro beam element and the micro connection element were used to analyze the progressive collapse resistance of plane frames and space frames,in which the failure criteria proposed by the theoretical analysis were adopted,The results showed that the simplified multi-scale model was in consistence with the test results.With the features of easy to model,high operating efficiency,and relatively high accuracy,this simplified multi-scale model can be used to analyze the structural behavior against progressive collapseBy combining theoretical analysis、experimental study and numerical simulation,this dissertation made a systematic research on progressive collapse resistance of CFSTCB frames,discussed internal forces,failure mechanism and the main resistance mechanism of the structure under collapsed conditions,defined structural collapse stages based on the development of plasticity and strain of the cross section of the beam,proposed the structural collapse criteria,deduced calculation formulae for the resistance-defonnation of CFSTCB and CFSTSB frames,and developed a simplified multi-scale model incorporating the macroscopic beam element and the microscopic connnection element.