Collapse Studies Of Steel Frame With Buckling Restrained Braces On Vector Form Intrinsic Finite Element Method

Traditional building structures increase the structural rigidity by increasing the crosssectional area of members.Although this method improves the progressive collapse resistance and earthquake collapse performance of the structure,it increases the construction cost of the structure and reduces the cost performance of the structure.As a load-bearing energy dissipation member,buckling restrained braces(BRB)has the advantages of easy installation,easy replacement,and excellent shock absorption effect,widely used in construction projects.At present,domestic and foreign scholars have more mature researches on the technology of BRB,but there are less researches on the progressive collapse and seismic collapse resistance of the frame structure with BRB.Vector form intrinsic finite element(VFIFE)is currently used to deal with large structural deformation problems.The discrete particles can be used to describe the motion behavior of the structure through its motion equation.There is no need to integrate the structural stiffness matrix during the calculation process.In view of the unique advantages of VFIFE,based on the vectored finite element theory,this thesis studies the vertical progressive collapse of the structure through the instantaneous unloading method,and uses the incremental dynamic analysis method to study the lateral seismic collapse of the structure Process simulation.The main research contents are as follows:(1)Introduce the basic concepts and analysis methods of the vectored finite element method,establish a steel frame model of the BRB unit and additional BRB based on vector form intrinsic finite element theory,and propose corresponding analysis methods;The nonlinear response of the steel frame structure with BRB is compared with the simulation results of VFIFE and SAP2000 to verify the correctness of the program.(2)Establish a six-story,four-span steel frame model,and use the equivalent instantaneous unloading method considering the initial deformation to analyze the vertical continuous collapse of the bottom member of the structure,and study the effect of the failure position of the bottom column,the position of the BRB,and the stiffness of the BRB on the dynamic response of the remaining structure under the vertical uniform load.And according to the vertical progressive collapse resistance of the structure and the economics of use,analyze the appropriate lateral stiffness ratio for the BRB frame structure.(3)Based on the incremental dynamic analysis method,the dynamic nonlinear analysis of the suitable lateral stiffness ratio frame is performed to analyze the effect of the BRB on the seismic collapse resistance of the structure,and analyze the fragility of the BRB steel frame under different damage states;(4)Establish the fracture criterion and fracture mode of beam element,column element and BRB element.Based on the VFIFE,simulate the process of fracture and collapse of the structure when the two bottom columns fail and are subjected to horizontal seismic loads,whether the steel frame with the BRB is arranged.And analyze the effect of the BRB on the fracture and collapse of the frame structure.