Progressive Collapse Studies Of Semi-rigid Connected Steel Frames Based On VFIFE Method

In the analysis of steel structure,the connection between beam and column is usually considered as ideal articulation or rigid connection.Although this ideal assumption simplifies the complexity of the structure,the connection between beam and column can neither be completely rigid nor ideal articulation in practical engineering,but is a semi-rigid connection whose mechanical performance is between the two.The adoption of ideal rigid connection or articulation model will result in it.There are great differences between theory and practice.At present,scholars have fully studied the mechanical behavior of semi-rigid joints,but there are few studies on the continuous collapse of steel frame structures considering semi-rigid joints.Therefore,the anti-continuous collapse performance of semi-rigid connection steel frame structure is studied in this paper.Vector form intrinsic finite element(VFIFE)is a new analytical method.It describes the shape of structure by the properties of particles,and uses Newton's second law as the particle motion criterion.It has unique advantages in solving complex problems such as large deformation,collapse and fracture.Based on the vector finite element theory and the instantaneous unloading method,this paper establishes a structural model considering the initial deformation.It mainly studies the continuous collapse failure behavior of plane steel frame structures from three aspects: the identification of key components,the dynamic non-linear analysis of semi-rigid joints and the numerical simulation of component fracture.The main research contents are as follows:(1)The advantages of vector finite element method in dealing with complex structural behaviors such as collision,collapse and fracture are introduced.The basic theory and analysis flow of vector finite element method are elaborated in detail.Based on this theory,semi-rigid connection elements are established.The correctness of the program is verified by comparing with the results of previous literatures;(2)In view of the need to determine the location of the dismantled component when the dismantled component method is used to analyze the continuous collapse of structures,this paper combines the advantages of the vector finite element method which can deduct the rigid displacement to calculate the pure deformation displacement,and analyses the structures with different spans,loads and layers,and obtains the key component positions of the corresponding structures.(3)The influence of semi-rigid connections on collapse resistance of steel frame structures is studied.By analyzing the variation of displacement and internal force of the residual structure before and after column removal,the influence of joint stiffness on the internal force redistribution of the residual structure under unbalanced load is studied.(4)According to the fracture criterion and mode of plane beam element,the fracture program of semi-rigid joint element is compiled with MATLAB software.The collapse process of semi-rigid joint steel frame structures under vertical uniform load and horizontal seismic load is tracked,and the influence of joint stiffness on collapse and failure of steel frame structures is analyzed.