| Steel structure has the advantages of good seismic performance,easy to assemble and light weight with high strength,but the previous earthquake shows that the welded beam-to-column connection of steel frame are prone to brittle fracture due to welding structure and welding defects,etc.At the same time,the energy dissipation mechanism of plastic hinge at the end of frame beam in earthquake also causes that the whole structure is difficult to repair after earthquake,resulting in serious economic losses.How to improve the tenacity of the structure to prevent the buildings from collapsing and achieve the fast restoration of the structures after the earthquake has become the forefront and hot spot of the research of earthquake prevention and mitigation at home and abroad.It is very important to develop a new type of steel structure system with low damage,easy to assemble and easy to repair,which can improve the ability of collapse resistance and quick recovery.In view of the shortcomings of the existing ductile steel beam-to-column connection,this paper proposes a kind of ductile steel beam-to-column connection based on the suspension,which includes the cantilever beam and the middle beam.They are connected by the suspended part of the beam’s upper flange and the buckling restrained plate of the beam’s lower flange,which forms the truss system to transfer the moment and shear of the connection.The connection uses the suspension part as the rotation center to rotate,which cause the connection’s opening and closing deformation.The deformation leads to BRP’s tensile and compressive plastic deformation which concentrated energy consumption,achieving the purpose of damage control and replacement after earthquake.In this paper,the mechanical model,seismic performance,functional recoverability and seismic performance of the connection are systematically studied.The main research contents and conclusions are as follows:(1)In the second chapter,the construction and work principle of the new type of ductile beam-to-column conection are introduced in detail.According to the preset working mechanism,the formulas of the new type of connection,such as the elastic lateral stiffness,the relationship between bending moment and rotation angle,the relationship between the interlayer lateral displacement and BRP deformation,are proposed preliminarily.Based on the damage control,the seismic design method of the new type of connection is proposed preliminarily,which provides the theory for the comprehensive analysis of the mechanical properties of the connection.(2)In the third chapter,the seismic test research including nine new type of beam-tocolumn connections is carried out,considering the influence of the parameters such as the setting of floor slab or not,different suspension connection structures(suspension bolting,suspension welding,suspension inverted welding).At the same time,the BRP of three new type connections with floor slab is replaced after the loading is completed,which is investigated the function recoverability after the earthquake,and the traditional beam-to-column connections are compared.The test result shows that the new type of connection can transfer the seismic energy to BRP which dissipates it centrally,so that the end of beam can keep elasticity under 4% displacement angle,and effectively avoid the flange buckling and fracture of the traditional welded connection;the suspension part can be used as the fixed rotation center of the connection to produce the opening and closing deformation at the lower flange of the beam,and reliably transfer the moment and shear of the connection;the suspension bolting and suspension welding construction is more advantageous to reduce the floor restraint effect,improve the bending capacity and the symmetry of the hysteretic performance of the connections.The seismic performance of the repaired new connection with floor slab is basically the same as that of the first load,which proves its good functional recoverability after earthquake.(3)In the fourth chapter,the finite element parameter analysis of the mechanical properties of the new beam-to-column connection is carried out,taking the beam height,joint location and BRP energy dissipation length as the variable parameters,and the finite element results are compared with the theoretical calculation results of mechanical theory.The analysis results show that: it is arranged at the reverse bending moment point of the beam under the vertical load which minimize the influence on the seismic performance of the suspended connection;Under different parameters,the new connection can achieve the preset goal of controlling damage,the hysteretic curve is full and stable,the theoretical calculation results of the performance parameters in the lateral stiffness,yield moment and rotational elastic stiffness of the connection are in good agreement with the finite element results,which proves the generality and effectiveness of the design method.(4)In the fifth chapter,the seismic performance of multi-story steel frame structure with new beam-to-column connection is studied.The structural modal analysis gravity analysis,static pushover analysis and dynamic time history analysis are carried out for three-story and nine-story space steel frame structure respectively.The yield order and deformation mode are analyzed,and compared with the elastic-plastic dynamic time history analysis of traditional steel frame structure with the same number of floors.The analysis results show that: the frame with the suspended beam-to-column connection can achieve the yield at the nodes of each floor,disperse the energy consumption of the structure,which is conducive to reduce the appearance of the weak layer of the structure;reduce the development degree of the plastic hinge at the column base and other parts,delay its appearance time;the acceleration response of the frame with suspended connection is smaller,the distribution is more uniform,and the seismic performance of the steel frame is significantly improved. |
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