| Concrete-filled steel tube(CFST)frame structure is widely used in construction engineering due to its advantages such as low template demand,high bearing capacity,fast construction efficiency and steel saving.Column base joint and beam-column joint are the key parts affecting the seismic behavior of CFST frame structure,while the stress of T-shaped column base joint and beam-column joint of multi-cavity CFST is more complex,so it is necessary to study them in depth.Based on the traditional horizontal socket beam-column joint and concrete-filled steel tube column base joint,this article aims to improve the on-site construction efficiency of beam column nodes and reduce the amount of steel used in column base joint.A new vertical socket beam-column joint and a column base joint with rolled steel plate replacing part of steel tube are developed respectively.The seismic behavior of vertical socket beam-column joint and T-shaped steel tube + rolled steel plate column bases joint is studied by combining low-cycle reversed loading test with ABAQUS finite element numerical simulation,which provides reference basis for engineering application.The main work and conclusions of the paper are as follows:(1)A new vertical socket beam-column joint with cantilever beam overlapping the bracket from up to down is proposed.The reliability of vertical socket beam-column joint is verified by low-cycle reversed loading test with conventional horizontal socket beam-column joint as a control specimen.After the fracture of the steel beam weld in the new beam column joint,no through section was formed and it still has plastic deformation capacity;Fracture of weld on steel beam flange is one of the main factors influencing failure mode of specimens.Through comparative analysis of test data,it is found that the ductility coefficients of the HSC and the VSC are 1.22 and 2.07 respectively,and the maximum equivalent viscous damping coefficients during loading are 0.188 and 0.250 respectively.The vertical socket beam-column joint has better plastic deformation capacity and energy consumption capacity,and has better bearing capacity after fracture of steel beam weld.(2)A scheme for refined numerical simulation of concrete-filled steel tube column-steel beam joint considering welding residual stress is established.To accurately simulate the influence of welding residual stress on the joint force,the temperature field of the moving heat source calculation model is applied and the model residual stress field is calculated by using the temperature field date.The residual stress is calculated by the uncoupled thermalmechanical analysis method and the residual stress is applied in the welding affected area in the form of internal stress in the beam-column joint quasi-static model.The hysteresis curve and stress nephogram are compared with the test results,the failure phenomena,strength and stiffness degradation process during the simulation loading process are in agreement with the test,and the simulation results are in good agreement with the test results,verifying the soundness of refined numerical simulation scheme.(3)Through finite element extended analysis,the influence of the U-shaped bracket thickness and bolt quantity on seismic performance of vertical socket beam-column joint under low-cycle reversed load is further explored,and the quasi-static analysis of vertical socket beam-column joint in ABAQUS under several conditions is completed.The results show that the thickness of bracket is not the main factor affecting the seismic behavior of vertical socket beam-column joint.With the decrease of the thickness of bracket,the stress of bracket in the model gradually increases.When the thickness of bracket is 4 mm,the stress near bolt holes reaches the yield strength.After the steel beam flange weld fracture,the lateral bearing capacity of the vertical socket beam-column joint decreases with the decrease of the bolt number.When the number of single row bolts is 2,the bracket stress reaches the yield strength in a large area.(4)A steel tube + rolled steel plate concrete column base joint with rolled steel plate instead of steel tube in part of cavity is proposed.The reliability of the steel tube + rolled steel plate concrete column base joint is verified by low-cycle reversed loading test with the conventional steel tube concrete column base joint as the control specimen,and its failure mode and hysteretic behavior are basically the same as that of the traditional column base joint.Finite element model of column base joint is established by ABAQUS.The accuracy of finite element model is verified by comparing the hysteresis curve and stress nephogram with the test results.Through comparative analysis of finite element models of the two specimens,it is found that the steel plate stress in the flange rolled steel plate cavity is small and the concrete stress is large during the loading process of the new type of column base joint,which indicates that the restraint ability of the rolled steel plate to concrete is weak.Combined with the stress of the web rolled steel plate and the concrete in the steel tube cavity at the web end is smaller than that in the traditional column base joint.It shows that the concrete in the rolled steel plate cavity blocks the force transfer between part of steel tube and the rolled steel plate,which slow down the concrete crushing at web end. |
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