| In the cold-formed steel structure,the common light-gauge steel system is a decentralized bearing system,with inflexible architectural space,flexible components and small connection stiffness,which is generally not used in multi-storey and tall buildings.In this article,the coldformed steel moment frame structure adopting new combined cross-section member and connection construction can meet the requirements of low-rise and multi-storey steel structures up to 6 floors,and has the advantages of flexible architectural space,high connection stiffness,simple installation and manufacturing.In this cold-formed steel moment frame structure with new combined cross-sections,the structural form and mechanical performance of the beam-column connections are critical to the overall structural performance.Therefore,four kinds of beam-column connections are proposed in this paper.The beam-column connections have good mechanical and seismic performance,the connection stiffness is large,and the components can be replaced,which can meet the different requirements of low-rise and multi-storey cold-formed steel moment frame for the bearing capacity and stiffness of connections.The four beam-column connections can achieve full bolt construction,no welding,and convenient installation,which can improve the sustainable development level of fabricated steel structure.In this paper,firstly,the research progress of cold-formed steel connections are summarized,and four kinds of new fabricated beam-column connections suitable for low-rise and multi-storey cold-formed steel moment frame structures are proposed,then the single cantilever beam cyclic tests of the connections are formulated,and the four kinds of beamcolumn connections are experimented.Secondly,the experiment results are processed to obtain and analyze the mechanical performance index and characteristics of the connections.Thirdly,four precise finite element models of connections are established,and the stress distribution and characteristics of each connection are discussed in depth.Then,combined with the experimental and numerical simulation results,the parametric analysis was carried out to study the influence of the parameters on the mechanical performance of the connections.Finally,four kinds of connections are classified,and the initial stiffness formulas of semi-rigid connections are derived by the component method,and its reasonableness and accuracy is verified by parametric numerical simulation results,in order to provide the theoretical basis for future engineering application.Through the above research and analysis,the main conclusions are as follows:(1)The failure modes of the four beam-column connections are similar.The results show that the plate’s curve and crack appear on the beam flange and web at the edge of the connection area.At the same time,the bolt hole on the beam has extrusion deformation.(2)The hysteresis loop shape of “end-plate type” connection JD1 is plump,and the connection area is always in the elastic stage.The other three kinds of connections show different degrees of slip characteristics and pinch phenomenon.The “channel steel connected type” connection JD2 has some loose slip,but the connection area is always in the elastic stage.There is some plastic development in the connection area of the “cross through-plate type”connection JD3 and “cross through-plate diagonal brace type” connection JD4.(3)The four kinds of beam-column connections have ductile failure and good seismic performance,which can effectively delay the local buckling and plastic development of the beam.And the ultimate bearing capacity is higher than the beam cross-section plastic moment,which proves the four connections can meet the requirements of "strong connection ".(4)When the end rotation of beam is equal to 0.02 rad which is the limit value of the elastoplastic interstory drift specified in the “Code for Seismic Design of Buildings”(GB 50011-2010),the bearing capacity of JD2,JD3 and JD4 is still in a linearly rising stage,and although JD1 is in the descending stage,its bearing capacity is still above 80% of the ultimate bearing capacity.According to the American “Seismic Provisions for Structural Steel Buildings”(AISC341-16),JD1 meets the requirement of Intermediate Moment Frames(IMF),JD2,JD3 and JD4 meet the requirement of Special Moment Frames(SMF).The initial stiffness of JD4 is the largest,followed by JD3 and JD1,and the lowest is JD2.(5)The precise finite element model established in this paper fully restores the actual loading of bolts pretension,the contact between parts,load and boundary conditions,etc.It can be found that the precise model can simulate the force condition of the connections well.which is reasonable and accurate.(6)For the “end-plate type” connection JD1 and “channel steel connected type” connection JD2,the thickness of connector has a great influence on the initial stiffness and the development of connector’s plastic deformation;the vertical spacing of bolts on column has an obvious impact on the initial stiffness;the ultimate bearing capacity is restricted to the beam.(7)For the “cross through-plate type” connection JD3,the thickness of through-plate,the height of through-plate,the size of beam section and the spacing of bolts on the beam web have obvious influence on the initial stiffness;in this connection,the ultimate bearing capacity is restricted to the beam.(8)According to the classification standard of Eurocode3,the connections are classified through the initial stiffness.In the unbraced frame system,JD1 and JD2 are semi-rigid connections,JD3 and JD4 are rigid connections.(9)The initial stiffness formulas of semi-rigid connections JD1 and JD2 are derived by using component method,and compared with parametric numerical simulation,the results prove that the formulas can predict the initial stiffness of connections well,which have the universality to some extent. |
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