Study On Cyclic Behaviour Of A Novel Steel Beam To Prefabricated Square CFST Column Connections

Concrete-filled steel tubular(CFST)column have been popularly used in high-rise buildings with outstanding seismic performance.In recent years,the prefabricated buildings have been developed rapidly in China.Many studies have been conducted for the steel beam to the prefabricated CFST column connections.The welded connections are widely used in the joint of the steel beam to CFST column.However,the connection quality is unstable by on-site welding and it also cannot meet the requirements of assembly efficiently.Blind bolted connections make the assembly connection between the steel beam and the CFST column come true.However,with poor stiffness and flexural bearing capacity,the steel beam to CFST column with blind bolted connection cannot satisfied the requirement of standards.However,the stiffness and strength of the blind bolted connections can be efficiently enhanced by the higher anchoring length and the lower width-thickness ratio.On the other hand,the anchoring length is restrained with the dimension of cross-section,and it is uneconomic for the lower width-thickness ratio resulting the thicker tube wall.Therefore,a novel anchor plate anchored sleeve bolt is presented to solve the poor performance of the blind bolted connection.The mechanical behaviors of the anchor plate anchored sleeve bolted connections are investigated by experimental research,finite element simulation and theoretical analysis.The main works can be summarized as follows:(1)Twenty-three anchor plate anchored sleeve bolts within concrete and CFST column were conducted with pullout tests.The anchorage performance of the connector was analyzed by test parameters of the anchor plate dimensions,anchoring length,steel tube restraint,edge distance,and group effect.Based on the failure mode and the strain analysis,the anchoring mechanism of the anchor plate anchored connector was studied.The calculation method of the stiffness and bearing capacity of the connection,and a simplified model of force-displacement curve are proposed.The results show that the stiffness is influenced by the anchor plate dimensions and edge distance,and the group effect is not obvious.The anchoring mode of concrete is influenced obviously by the edge distance,when the edge distance less than anchoring length,the concrete strut mode was form between the tube edge and anchor plate,and the theoretical and experimental results are in good agreement.(2)Six cyclic loading tests of the steel beam to prefabricated CFST column with anchor plate anchored sleeve bolted connections were carried out.Connection details,end plate thickness,axial load level,and beam-column linear stiffness ratio were tested to investigate the mechanical properties of the novel connection.The failure mode and load-deformation curves were obtained from the test.Based on the test results,the mechanical properties of the connections,such as stiffness and bearing capacity,ductility and rotational capacity,stiffness and strength degradations,and energy dissipation capacity were studied.It is concluded that the connection is the rigid connection in non-sway frame and with good ductility and energy dissipation capacity.The stiffness and strength degradations,and energy dissipation capacity were decreased with lower beam to column linear ratio.The plastic deformation of the steel beam was affected by the thickness of the end plate,the steel beam cannot form the plastic hinge with the thinner end plate.It reduced the energy dissipation capacity of the connection.(3)The finite element(FE)analysis models of the steel beam to prefabricated CFST column with anchor plate anchored sleeve bolted connections are studied by ABAQUS.The behaviors of the connections during the test are analyzed by the verified FE model.The parameters of end plate,axial load level,concrete strength,and the anchoring parameters were investigated.It is concluded that the stiffness and strength of the connection are improved effectively with thicker endplate and endplate stiffener,the effect of the axial load level and the concrete strength can be ignored,when the they are greater than 0.2 and C50,respectively.Increasing the anchoring length and anchor plate thickness also improved the stiffness and strength of the connections.(4)The calculation methods of the initial rotational stiffness and the flexural bearing capacity of the steel beam to prefabricated CFST column connections with anchor plate anchored sleeve bolted are proposed by the theoretical studied.A simplified tri-linear model of the moment-rotation curve is also proposed and verified with the test results.Based on the experimental and theoretical results,it suggested that the connection stiffness coefficient of 1.7.Moreover,the design flexural bearing capacity of 1.5M_p is recommended to calculate the endplate thickness.Moreover,it is recommended to use steel beam of S1 section,concrete strength higher than C50,and the gas shielded welding.To provide reference for further research and application.