Analysis Of Progressive Collapse Resistance Of Steel Frame And Construction Of Equivalent Model

The so-called progressive collapse is the result of local structure damage or partial substructure damage because of the accident,and triggered a chain reaction that causes damage to other parts of the structure,resulting in a wide range of structural collapse phenomenon.Due to the progressive collapse analysis relates to elastoplastic,large deformation and nonlinear factors and are often associated with the time.Thus,the precise progressive collapse analysis and design of the structures is confronted with many difficulties,how to correctly,reasonable anti progressive collapse analysis and design become an important issue to be solved by structural engineers.In this situation,the steel frame structure as the research object,by builded the three level structural models of progressive collapse analysis,frame structure,frame substructure and single-layer substructure,to explore the simplified method and the equivalent mechanism,mainly for the following research work:(1)On the basis of the good ductility of steel and the general internal force conditions of the bending members and the pull bending members,the theoretical model of resistance development curve and the load displacement model of the restrained steel beam are put forward,after the failure column were removed.Under the action of vertical load,the restrained beam has undergone a process of development from the beam mechanism to catenary mechanism,the beam end resistance that is divided into elastic beam mechanism stage,elastoplastic beam mechanism stage,catenary mechanism development stage.The factors of the formation and development of the beam mechanism,catenary mechanism are analyzed,including material intensity,beam span to depth ratio,the size of beam section and boundary conditions.(2)By Pushdown elastic plastic static analysis method,the resistant characteristics of each layer beam of a 10 story plane steel structure under vertical load was analyzed,whose bottom middle column was failure.At this time,each floor beam relies not only on single beam mechanism(catenary mechanism and beam mechanism)to provide resistance,but also forms a similar “deep beam” combination mechanism to resist external loads.Resistance provided by “deep beam” combination mechanism accounted for most of the total resistance and usually only the bottom of the beam by beam mechanism into the catenary mechanism.(3)Based on component constraint stiffness analysis,the study of the steel frame structure is proposed,which can equivalent the frame structure to frame substructure and single-layer substructure by the spring boundary for analysis.By using the finite element software ABAQUS,the elastic dynamic analysis shows that the simplified model has good reliability in the elastic stage.(4)By using the elastic dynamic analysis method and pushdown elastic plasticity static analysis method discusses the reasonableness of single-layer substructure equivalent model of the structure which is different from constrained beam.The results show that peripheral component of single-layer substructure considered in the actual structure analysis and design is very necessary.