Seismic Performance Analysis Of Buckling Restrained Braces And Special Center Braced Frames With Cast Steel Connector

In the design of high-rise steel frame structures,the Moment-Resisting Frames structure(MRFs)has smaller lateral stiffness and larger lateral displacement under the lateral load,so it is difficult to meet the seismic requirements.The.Concentrically Braced Frames structures(CBFs)have great lateral stiffness under elastic working condition,and it has good seismic performance under small earthquake action.However,under the action of large earthquakes,the brace is easy to buckling and destabilize,so that the rigidity and energy consumption capacity are drastically reduced.The Special Concentrically Braced Frames structures(SCBF)is introduced into the structural design as a good seismic performance structure.Compared with the common Concentrically Braced Frames,the design of the brace and connection have changed greatly.The brace unit is composed of the hollow section brace and the joint plate,which not only has large stiffness but also is more economical.However,the results of the research on the SCBFs show that the current design method hinders the full play of the brace.The main manifestations are as follows:(1)the weld seam of the welded joint plate is torn;(2)local buckling and post buckling problems appears in the hollow section braces which need reinforcement after earthquake.(3)The gusset plate undergoes out-of-plane buckling,yielding,and even tearing.The inelastic deformation performance of SCBFs is controlled by the buckling,postbuckling and yielding of the bracing members and connectors.Therefore,in order to ensure the large non-elastic deformation of the brace under large earthquakes without brittle failure and low-cycle fatigue failure,this paper proposes a bracing member to be designed as an bucklingrestrained brace with ductile cast connectors.On the one hand,the inelastic deformation of the structure is concentrated on the energy dissipation section of the cast steel.It can improve the seismic performance of the structure,alleviate the stress concentration of the node area,improve the reliability of the joint and the low cycle fatigue life of the structure,and Cast connectors can also be used as a replacement element to repair the structure after the earthquake,reduce the cost of repair,and make the structure restore the seismic performance quickly.On the other hand,the buckling restrained brace of double steel tube is used to replace the ordinary hollow section brace,to improve the energy dissipation capacity of the brace and to solve the buckling problem of the support,and to form a special central support steel frame system with ductile cast connectors.Through the above changes,the purpose of improving the structural performance and improving the seismic performance of the structure is achieved.At the same time,the introduction of cast steel not only reduces the inspection time and repair cost of the structure after the earthquake,but also provides a new idea for the application of the assembly node,which has important theoretical significance and broad prospects for engineering application.In order to study the mechanical properties of buckling-restrained brace and steel frames with cast connectors,finite element analysis and experimental studies were used to study the mechanical properties of the bracing members.The framework uses finite element analysis method to study its mechanical performance,and the conclusions are as follows:Firstly,Through finite element analysis,it can be seen that under unidirectional and cyclic loads,deformation of the specimen is mainly concentrated in the energy-consuming section of the cast connector,achieving the goal of concentrating the non-elastic deformation of the brace member on the cast connector.Secondly,Through experiments,it is found that the bracing members with bolt connection type and welded type cast connectors have good energy dissipation performance.The width to thickness ratio of stiffeners and energy dissipation plate,the axial force ratio and the length of energy dissipation section are important parameters affecting the seismic performance of the specimen.Thirdly,The finite element analysis of the failure mode of the specimen is in good agreement with the experiment results,which verifies that using the finite element to simulate the experiment has certain reliability.Fourthly,Through the finite element simulation of the Special Concentrically Braced Frames with cast connectors,the hysteretic curve of the structure is fusiform,indicating that it has good seismic performance.