Research On Seismic Behavior Of Semi-rigid Joints Of Knee Brance Reinforced Steel Frames

In this thesis,a new type of composite joints used in semi-rigid connection steel frame structure is proposed,that is,the corner braces strengthen the end plate connection semi-rigid joints.By adding small buckling restrained energy dissipation corner braces near the beam and column connection joints,the purpose of seismic energy dissipation is realized.The energy dissipation corner brace components are small and can meet the needs of various building functions.Although the traditional semi-rigid connection joints are installed flexibly and have certain seismic energy dissipation capacity,compared with the rigid connection joints,the semi-rigid joints will have large deformation under large earthquakes,and the failure forms are mainly end plate breaking or bolt hole pulling off,which is brittle failure,which is unfavorable to the seismic performance of the structure.Therefore,the energy-dissipation brace can be added on the basis of semi-rigid joints.The energy-dissipation brace is composed of the energy-dissipation core plate of the brace,the external buckling restrained sleeve and the unbonded rubber elastic cushion between the sleeve and the core plate.The layout of the energy-dissipation brace not only solves the problem of low lateral stiffness of the original steel frame structure,but also solves the problem of inflexible spatial layout of the traditional buckling restrained brace.It can not only improve the bearing capacity and lateral stiffness of the structure under small earthquakes,but also play a role in energy dissipation under moderate and large earthquakes.It has good practicability.In general,the semi-rigid joint with corner brace strengthened end-plate connection has good seismic energy dissipation capacity,and has the advantages of convenient installation,flexible arrangement,convenient repair and easy replacement of energy dissipation corner brace after earthquake damage,which has a good prospect in future engineering design and application.Scholars at home and abroad have carried out some research on semi-rigid joints and energy dissipation corner braces.Firstly,this thesis explores the strengthening effect of energy dissipation corner braces on the mechanical indexes of semi-rigid joints connected with extended end plate by ABAQUS finite element software.At the same time,it also explores the bearing capacity,energy dissipation capacity and failure mechanism of composite joints under the combined action of semi-rigid joints with different end plate thickness and energy dissipation corner braces with different core plate section sizes.Finally,the simulation parameter analysis is carried out to explore the relationship between the overall stiffness of semi-rigid joints strengthened by corner braces and the stiffness of corner braces and semi-rigid joints,and the concept of optimal stiffness ratio is introduced.The optimal combination form of semi-rigid joints and energy dissipation braces can be obtained by finite element simulation,and then the optimal stiffness ratio of energy dissipation braces and semi-rigid joints is obtained.Finally,the optimal stiffness ratio of each group is obtained by regression analysis.The calculation formulas of the optimal stiffness ratio K with regard to the cross-sectional area of the core plate of the brace A_s and the thickness of the end plate of the semi-rigid joint b as independent variables are obtained,and the relevant calculation methods are proposed.Through the finite element analysis results,it can be seen that the mechanical performance of the corner brace reinforced semi-rigid joint is better than that of the traditional pure semi-rigid joint,and the failure mode is more reasonable.The addition of energy dissipation corner brace can significantly improve the stiffness and bearing capacity of the joint under strong earthquake,and can protect the main structure and give full play to the role of the structure’s fuse.It provides a theoretical basis and design guidance for the comprehensive application of energy dissipation corner braces and semi-rigid joints in practical engineering,and lays a foundation for further research on the follow-up corner braces and semi-rigid joints.