Collapse Studies Of Semi-rigid Steel Frame With Buckling Restrained Braces

The structure with semi-rigid connection is superior in ductility and energy dissipation capacity,and has good seismic performance.However,the structural system with semi-rigid joints has lower lateral rigidity and larger lateral displacement.Therefore,researchers put forward the method of adding braces to the semi-rigid frame structure to optimize the structural system.Buckling restrained braces（BRB）possesses almost the same mechanical performance in tension and compression,and obvious advantages compared with ordinary braces.When applied to semi-rigid structure,the BRBs’ existence can give full play to the advantages of semi-rigid joints and improve the lateral rigidity of the structural system.However,ordinary braces are widely involved in the current research,and the research on collapse of buckling restrained brace semi-rigid structures is relatively few.Therefore,the collapse resistance of BRB semi-rigid steel structure is studied in this thesis.Vector form internal finite element（VFIVE）discretizes the continuous structure into the basic "computing carrier"-the particle,which retains its original properties and states,and the deformation of the structure is described by the classical force and motion relationship Newton’s second law.The VFIVE shows obvious advantages in dealing with the strong nonlinear problems such as large deformation and collapse.In view of this,based on this method,the collapse resistance of the structure is studied in this thesis,the main research contents are as follows:（1）The theory and calculation method of vector finite element are described in detail.Meanwhile,the simulation method of semi-rigid joints and buckling restrained braces based on vector finite element theory is described,and the corresponding VFIVE analysis model is built.By comparing the calculation results of the program,programmed with MATLAB,and the existing analysis software,the correctness of the program is verified.（2）The response of the remaining structure under vertical load is analyzed by using the instantaneous unloading method;the influence of the location of the failure column and the rigidity of the BRBs on the dynamic response of the residual structure is studied;by changing the rotational rigidity of semi-rigid joints,the influence of joint rigidity on the remaining structure is studied.Research shows: the change of the rotational rigidity of the semi-rigid connection will affect the performance of the BRBs.The existence of buckling restrained braces can significantly improve the ability of internal force redistribution and vertical progressive collapse resistance of semi-rigid steel frames.（3）The dynamic time-history analysis of the structures with a group of different support rigidity is carried out by using a group of seismic records.The influence of the change of support rigidity on the response of the structure under horizontal earthquake is explained by using the maximum inter-story drift ratio of the structure,the hysteretic state of the support,and the time history of the vertex displacement,etc.,and the selection range of rigidity,making the BRBs better performance,is given.The incremental dynamic analysis of the structure model is carried out by selecting the support stiffness suitable for the calculation example in this thesis.By comparing the evaluation indexes,it is proved that the BRB semi-rigid structure shows good seismic collapse resistance.（4）Based on the simplified fracture mode and criterion established by vector finite element theory,the vertical progressive collapse and horizontal earthquake collapse process of semirigid steel frames with and without buckling restrained braces are simulated.The analysis results show that the dynamic response of semi-rigid steel frames with BRB is reduced and the structure possesses high collapse resistance.