Vertical Progressive Collapse Analysis Of Steel Frame Structures With Viscous Dampers

The process of progressive collapse of the building structure involves complex nonlinear mechanical behavior,such as large deformation,large rotation and elastoplastic,so the analysis program should be able to change the stiffness matrix and geometry of the structure instantaneously.The existing finite element method has some limitations in the analysis of crack and collapse behavior of structures.Vector Form Intrinsic Finite Element(VFIFE)is a new numerical calculation method based on Vector Mechanics and numerical calculation,it shows unique advantages in solving complex problems,such as large deformation,large rotation,collapse and so on.The nature of the progressive collapse of structure is a dynamic response.Damping can absorb energy and reduce the amplitude.The viscous dampers were used in the progressive collapse analysis of steel frame structures based on the idea of energy dissipation,and the progressive collapse resistance and failure mechanism of energy dissipation structures were deeply studied.The elastoplastic model with initial deformation condition for dynamic progressive collapse analysis was constructed,the Transient Unloading Method(TUM)with integration of static and dynamic analysis before and after component removed was proposed based on VFIFE.In this paper,the progressive collapse dynamic behavior of steel frame structure was studied in three aspects,which are the influence factors of structural progressive collapse,the progressive collapse performance analysis of energy dissipation structures and the numerical simulation of fracture collapse.The main research contents are as follows:(1)By comparing the calculation difficulties of finite element method,discrete element method and discontinuous deformation analysis in structural fracture collapse analysis,the advantages and characteristics of VFIFE in dealing with complex behavior such as structural fracture collapse were introduced.The basic theory of the VFIFE was described in detail,and the effect of the damper was simulated by applying the external force between the two particles.The numerical example was used to verify the accuracy of the dynamic analysis of the plane steel frame structure and the viscous damping element program.(2)The dynamic nonlinear analysis of plane steel frame structure was carried out by TUM.The index of the vertical displacement and the rotation displacement magnification factors were proposed.The effect of the failure position of the bottom column,the failure time of the component and the yield strength of the material on the dynamic response of the residual structure were studied,and the corresponding suggestions were given for the different factors to provide reference for improving the vertical progressive collapse performance and engineering design of the structure.(3)The performance requirements of the viscous dampers in the structure resistance to progressive collapse was studied.Through the variation of the internal force before and after removing the column,The dynamic effect area and internal force transfer mode caused by unbalanced load on the top part of the residual structure with dampers were studied,and the influence of the arrangement of the dampers on the change of the yield strength of the material was discussed.(4)The fracture criterion and mode of the beam elements were established based on VFIFE,and the structural fracture program was written by MATLAB.The fracture collapse behavior of setting and not setting viscous dampers on the steel frame structure under the two loading models of the bottom column failure and the horizontal seismic action was numerically simulated.The process of structural fracture collapse was predicted and tracked,and the failure process of progressive collapse was studied.The role of viscous dampers in the fracture collapse of structure were compared and analyzed.