Experimental Study On Hysteretic Behavior Of Circle Tubular Steel Members Under Variable Axial Loads And Cyclic Lateral Displacement

Circular hollow section steel tubes are widely used in large-span spatial structures.Under strong earthquakes,the inner force responses boundary in large-span spatial structure components are complex,generally existing axial force,shear force and bending moment with varying force and large amplitude.Therefore,many different degrees of damage and fracture failures of CHS components was frequently reported.But in seismic events,indicate that there is still a lack systematic study of hysteresis behavior under complicated stress state for CHS components currently,based on such a background,this paper focuses on the experimental study on the hysteretic behavior of CHS members under different loading modes.In addition,the finite element analysis is also performed to validate the effectiveness of numerical simulation method.The main work is as follows:(1)The smooth and notched strip specimens extracted from 20#hot rolled seamless CHS members were designed and processed,and the both uniaxial tension tests and ultra-low cyclic loading tests were carried out.The parameters of micromechanical models VGM under monotonic loadings and the parameters of micromechanical fracture model CVGM under ultra-low cycle loading were calibrated.The fracture predictions of notched specimens under cyclic loadings matched well with experiment results.(2)The experimental studies on the hysteretic behavior of eight full-scale CHS specimens under variable axial loads and cyclic lateral displacements had been carried out.The effects of the axial force loading and lateral displacement loadings varying synchronized,with difference phase as well as with frequency difference on the hysteretic behavior of CHS specimens were analyzed from the experimental phenomena,hysteretic curves,skeleton curves,energy dissipation capacity,ductility and fracture life.(3)Finite element models of specimens considering both weld and heat-affected zone were established with FEM software ABAQUS.And the sensitivity analyses were performed to determine the mesh size and initial geometric imperfections of models.Based on CVGM micromechanical model,continuum finite element analyses were carried out to generalize experimental findings.The results show that the numerical simulation method adopted in the study can accurately reflect the nonlinear hysteretic properties of CHS members.Within the scope of this study,the CVGM model can predict ultra-low cycle fatigue fracture of the tensile specimens accurately.However for those specimens subjected to the combination loadings of compressive axial force and bending moment,commonly used CVGM method fail to assess the ductility of specimens reasonably.