| Composite concrete filled steel tubular(CFRP)structure is a new type of heavy-duty column with inner steel tube,section steel or CFRP placed in ordinary concrete filled steel tubular columns.It has a series of advantages and broad application prospects,such as convenient construction,high bearing capacity and remarkable economic benefits.At present,the research of composite concrete-filled steel tubular structures mainly focuses on welded joints,but the occurrence of the Osaka-Kobe earthquake in Japan shows that the residual stress produced by welding has a great impact on the material properties of steel,which is very harmful to the seismic performance of the structure.The unilateral bolted joint of concrete filled steel tubular(CFST)is a new type of joint with good plasticity,toughness and seismic performance.This paper intends to study the unilateral bolted joints of composite concrete filled steel tubular(CFST).Based on the digital speckle correlation method(DSCM),the composite concrete filled steel tube(CFST)joints were tested,and the shear-shear angle(V-Y)hysteretic curve and skeleton curve in the core region were obtained.The shear resistance of the joints was studied,and the restoring force model of V-T curve was established according to the hysteretic law of shear deformation in the core region.The stress mechanism of the joints is studied by using the finite element software ABAQUS,which combines numerical simulation with experiment.Finally,the hysteretic behavior and shear deformation of the joints are studied by taking the axial compression ratio,yield strength of steel beams and steel tubes,pre-tension of high-strength bolts and strength of core concrete as parameters.The results show that:(1)The horizontal shear-shear deformation(V-Y)hysteresis curves and skeleton curves in the core region obtained by DSCM technology all show good energy dissipation ability.The maximum shear angle of the joint core is within 0.005rad.Compared with other types of joints,the shear deformation of single-side bolted joints of CFST is smaller.The initial shear stiffness and ultimate bearing capacity of T-joints can be significantly improved by stiffening,which meets the structural design requirements of "strong joints and weak members".(2)The load-displacement hysteretic curves obtained by ABAQUS finite element simulation are in good agreement with the test results,and all the simulated hysteretic curves are full and without pinching,and the skeleton curves are inverted S-shaped,which has good energy dissipation capacity.From the numerical simulation of stress distribution,it can be seen that the node can effectively transfer the load from the column end to the beam end.The maximum Mises stress is at the junction of T-shaped web and flange and at the high-strength bolt hole wall.In addition,the equivalent viscous damping coefficient he=0.368?0.437 of the specimens is much larger than the energy dissipation capacity of traditional reinforced concrete joints,which meets the requirements of seismic design of structures.(3)Core concrete strength and pre-tension of high-strength bolts have little effect on the initial stiffness of joints;with the increase of yield strength of steel beams,the shear deformation and ultimate bearing capacity of the model also increase,but the initial stiffness remains unchanged;within a certain range,with the increase of axial compression ratio,the initial stiffness and ultimate bearing capacity of joints will also increase,but the excessive axial compression ratio will be limited.The shear deformation decreases due to the trend of planar dislocation.When the Axial compressionratio is 0.7,the ultimate bearing capacity of the joint decreases,and the failure mode of the frame is that the column foot forms plastic hinge before the beam end. |
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