Study On Seismic Behavior And Finite Element Analysis Of Blind Bolted Connections Between Square Hollow Structural Section Column And H-beam

Square concrete-filled steel tubular column(CFST)have high ductility,compressive and flexural capacity,and have been widely used in practical projects.Owing to the characteristics of the closed section of tubular column,the connections between the square CFST column and an H-shaped steel beam are mostly welded.However,the square tubular column and the beam welding connection are more likely to undergo brittle fracture at the beam-end weld,and the welding quality is still the key controlling factor in the performance of welding connection.But it is difficult to guarantee the quality of this,because of various uncontrollable factors on the site.To solve this problem,researchers have proposed endplate connections using bolts,which avoided the spot welding of connections.However,due to the closed-section characteristics of the square hollow structural section column,it is difficult to achieve a high-strength bolt application,and the method of installing a hand hole on the column wall requires on-site repair welding,which affects the performance of the panel zone.To solve the difficult problem of installing high-strength bolts with closed section columns,a blind bolt,with one-side locking capability,was proposed and applied.In this paper,the seismic behavior and static performance of endplate connections to concrete filled tubular columns using STUCK-BOM are studied by experimental research and finite element analysis.Prior to the tests on the CFST connections,the monotonic tensile tests of six groups of blind bolts are carried out.The failure modes and causes of monotonic tensile specimens are studied.The bearing capacity,global tensile stiffness and slip stiffness of specimens were analyzed.The variation rules of tensile stiffness under different failure modes are revealed.The composition of tensile stiffness of blind bolts is summarized,and the raising principle of concrete and eccentric arrangement of blind bolts on the tensile stiffness of the test specimens were obtained.The test results show that filled concrete and eccentric arrangement of blind bolts have no effect on the ultimate bearing capacity of the specimens;filled concrete and eccentric arrangement of blind bolts can significantly improve the global tensile and slip stiffness of the specimens.After the concrete is destroyed,it will completely withdraw from the work and cannot continue to provide tensile stiffness for the specimens.The mechanism of increasing tensile stiffness of filled concrete specimens is mainly to restrict the expansion trend of branch of unilateral bolt sleeve and increase the stress area of steel tube's tension flange.The mechanism of increasing tensile stiffness of eccentric specimens is to make full use of the stiffness of steel tube's side wall.In this study,the seismic behavior of blind bolted,extended endplate connections,using STUCK-BOM connections to square CFST columns,was investigated.Three 1/2-scale connections were tested under quasi-static cyclic loading,and the failure model,stiffness,ductility,rotation capacity,stiffness degradation and energy dissipation of the connections were evaluated in relation to varying material and geometric parameters.Compared with previous research results,the difference in seismic behavior between CFST connections and Hollow structural section(HSS)connections was investigated.By varying the thickness of the endplate and the type of blind bolt,the effects of different connection structures on the seismic behavior of the connections were analyzed.The test results showed that the filled-concrete can effectively anchor the blind bolt and restrain its pull-out trend;blind bolts are prone to elongate deformation,or slip,under external loads,resulting in a clear pinch phenomenon in the moment–rotation curves of the connections.The initial rotational stiffness of CFST connections was about 50% higher than that of HSS connection.The equivalent damping coefficient,dissipated energy capability,and ductility of CFST connections were higher than those of HSS connections.The ultimate rotation angles of CFST connection were 0.038-0.06 rad,which meets the requirements of the seismic design code for buildings.The ultimate rotation angles of the square CFST connections were 3.98-4.31 times the rotation angle limit of the flange-welded connection,under the same condition,this means the rotation stiffness of the connections is small.ABAQUS finite element software is used to model the connections between beam and square CFST column with blind bolt,and the static performance of the connections is analyzed.The finite element model can accurately simulate the initial rotational stiffness of the connection.Meanwhile,reasonable simplification method and meshing method are used to greatly improve the calculation efficiency of the finite element model.The results show that the finite element model can reproduce the actual failure mode of the connection and can be applied to the follow-up study of the connection.The simulation results are close to the test results,which verifies the accuracy of the finite element model.