Research On Low-cycle Fatigue Performance Of X-shaped Intersecting Circular Steel Pipe Joints Under Strong Earthquakes

The circular steel pipe intersecting joints are commonly used in the truss grid structure.Under strong earthquakes,the tubular joints of the circular steel tube bear large reciprocating loads,which may cause low cycle fatigue damage and cause the collapse of the structure.The study of the low cycle fatigue performance and evaluation criteria of tubular tubular joints under reciprocating load is of great significance to correctly grasp the seismic performance of the structure.In this paper,the ABAQUS finite element analysis software is used to predict the fracture of X type intersecting joints under monotonic tensile loading,and the low cycle fatigue performance of X type intersecting joints under reciprocating loading is analyzed.The main contents and conclusions are as follows:(1)The nonlinear finite element analysis of three X unstiffened CHS joints under monotonic tensile loading is carried out.The calculated data are extracted,and the fracture loads of VGM and SMCS fracture criteria are obtained under the monotonic tensile loading,and the load and the ultimate value of the bearing capacity calculated in the steel structure design code are compared and analyzed.(2)The finite element model is established for the design value of the bearing capacity and the X type intersecting node of three circular steel tubes with the same steel quantity.The nonlinear analysis is carried out.The equivalent plastic strain,effective plastic strain,Mises stress and Pressure stress are extracted,and the CVGM and DSPS fracture criteria based on the micro mechanism are obtained.The low cycle fatigue fracture location and low cycle fatigue life of intersecting joints under strong cyclic loading are determined.The results show that the low cycle fatigue life of X type intersecting joints increases with the decrease of the diameter of the branch of the branch,but the limit load of the fracture is reduced.(3)The hysteretic curve of the three node finite element model under the action of strong earthquake and complex load is extracted.When the beta is smaller,the hysteresis curve is more full,and the ductility and energy dissipation coefficient of each model are calculated.The effects of hysteretic properties,ductility and energy dissipation on the low cycle fatigue performance of joints are compared and analyzed.The results show that the diameter of the branch pipe has a significant influence on the ductility factor of the node,and has a certain influence on the energy dissipation coefficient.The ductility and energy dissipation coefficient decrease with the increase of the beta.The conclusions of this paper have a certain reference value for the analysis and evaluation of the low cycle fatigue performance of the tubular X type intersecting joints under the strong earthquake reciprocating load.