Analysis Of The Seismic Performance Of The Existing Steel Frame Structure Strengthened By Buckling-Restrained Knee Brace

Buckling-Restrained Knee Brace as a small buckling restrained brace is installed near the beam and column connection node.A new type of energy dissipation shock absorption structure system is formed after reinforcement in order to achieve the purpose of seismic reinforcement.The Buckling-Restrained Knee Brace components in this new reinforced structure system are small in volume and flexible in layout.It is convenient to reinforce,transform and install.It does not affect the building layout,and meets the needs of various building functions.At the same time,the Buckling-Restrained Knee Brace components not only solve the problem of low lateral stiffness of the original steel frame structure,but also solve the problem of uneven stiffness and inflexible spatial arrangement of the frame structure strengthened by buckling restrained brace.This paper uses YJK Building Software and MIDAS Gen structural finite element analysis software to reinforce and reconstruct the six story steel frame office building which was built 10 years ago in a certain area of Shenyang due to the change of use function and specification requirements.Buckling-Restrained Knee Brace and buckling restrained brace are used to reinforce the building structure and the mechanical properties of the whole structure after two kinds of reinforcement are compared and analyzed to provide theoretical basis for its realization in the actual project.This paper mainly studies the following problems and obtains some research results.The equivalent section area of the energy dissipating member is calculated by the equivalent section method.The simulation analysis of corner brace arrangement is carried out in YJK.On the premise that the maximum inter story displacement angle of the strengthened structure is less than the code limit,obtaining the optimal layout scheme of Buckling-Restrained Knee Brace for strengthening the existing building structure.The Buckling-Restrained Knee Brace members are simulated by MIDAS lag system,using construction stage analysis to simulate the existing load and self weight of corner brace in the process of structural reinforcement.This is reinforcement under load.The results show that the main body of the structure remains in the stage of elastic working range in the process of strengthening under load.Through the static elastic-plastic analysis,the layer displacement and layer displacement angle of the reinforced structure at the performance point are obtained.The results show that the storey shear force is smaller than that of the buckling restrained brace system,which shows that the internal force of the structure is smaller under the horizontal load and the rigidity of the structure is moderate.By comparing the structural capacity spectrum curve and plastic hinge state,it is concluded that the structural system with two strengthening methods has good mechanical performance.Through the dynamic time history analysis,under the frequent earthquake,the buckling restrained braced members start to consume energy when they reach the yield,but the Buckling-Restrained Knee Brace members remain elastic,which only provides certain lateral stiffness for the structure.Under the action of seismic fortification,the Buckling-Restrained Knee Brace begins to reach the yield energy consumption.Under the action of rare earthquake,the essence of Buckling-Restrained Knee Brace strengthening structure system is eccentrically braced steel frame system.The joint area of Buckling-Restrained Knee Brace and beam is subjected to the shear force produced by the seismic action,which makes it reach the yield before the beam column joint,and the energy dissipation is carried out under the inelastic deformation state.With the continuous earthquake action,it is first transformed into the plastic hinge in the joint area of corner brace and beam,cooperative energy consumption of corner brace and plastic hinge.Under the action of earthquake,the plastic hinge of beam column joint is moved out and the beam column joint is effectively protected,forming the “triple seismic fortification stage”.That is,“small earthquake support,medium earthquake energy consumption,large earthquake coordination”.It can meet the higher-order performance-based seismic target of “moderate earthquake is not bad,large earthquake can be repaired”.