Hysteresis Performance Test And Finite Element Analysis Of X-shaped Circular Steel Tube Intersection Node

In recent years,steel tubular joints have been widely used in various practical projects,such as airport terminals and gymnasiums,due to their good mechanical properties and simple and beautiful shape.The joint is often the first area where these steel tube structures break.The performance of the joint is related to the safety of the whole structure.Therefore,it is necessary to conduct in-depth research on the performance of the joint.Through the joint efforts of scholars at home and abroad,the research on the static performance of tubular joints has become mature and perfect.Relatively speaking,the research on the hysteretic performance of joints is still relatively small.In addition,the impact of fracture behavior on the hysteretic performance of joints is rarely considered in previous studies,leading to inaccurate evaluation of the seismic performance of joints,Only by reasonably predicting the crack initiation and propagation process of joints can the seismic performance of joints be more detailed and comprehensive evaluated.In this paper,the X-type circular steel tubular joint is taken as the research object,and two joint specimens with different welding forms are designed to carry out axial quasi-static tests.The crack initiation and crack propagation process of the joint are observed and recorded.After processing the test data,the hysteretic performance of the joint is investigated from the aspects of ductility,energy dissipation,stiffness degradation,etc.Subsequently,the test joints are finely modeled,and the VUSDFLD subroutine compiled according to the ductility criterion CVGM is embedded in ABAQUS.The finite element simulation of the test joints is carried out,and the simulation results and test results are compared to verify the applicability and accuracy of the subroutine used.The research results of this paper are as follows:(1)The failure mode of the two joints is the same,which is manifested as the main pipe wall tearing failure under tension and compression cyclic load.The crack initiation and development process of the two joints are similar.First,there are small cracks on the main pipe wall at the saddle point on the right side of the front of the joint,and then there are small cracks on the main pipe wall at the saddle point on the left side of the back.Then the cracks gradually develop from the crack initiation point along the intersection line to the crown point.The early crack development is mainly based on the length change,and the later crack length development is slow,mainly based on the increase of the crack width.(2)The hysteretic curve of CX-1 joint presents an inverse S-shape with obvious "pinch" phenomenon and poor seismic performance.The hysteretic curve of CX-3 joint presents an arch shape with slight "pinch" phenomenon and good seismic performance.The ultimate tensile bearing capacity of the joint is greater than the ultimate compressive bearing capacity.Before reaching the ultimate load,the increase of each level of load in the forward loading of the two nodes is greater than that in the reverse loading.When the ultimate load is reached,the bearing capacity of CX-1joint decreases sharply,while that of CX-3 joint decreases slowly.The ductility coefficient of the two joints is greater than 3,and the ductility is good.The ductility coefficient in tension is greater than that in compression.The cracks of both joints have been fully developed,but the crack development speed of CX-1 joint is faster than that of CX-3 joint,and its deformation capacity is inferior to the latter.The energy dissipation coefficient of CX-1 joint is close to 1 at the later stage of crack development,and the energy dissipation capacity is poor.The energy dissipation coefficient of CX-3 joint is greater than 1 at the time of crack initiation,and then gradually increases with the crack expansion,and the energy dissipation capacity is good.The stiffness degradation of CX-1 joint is fast,and that of CX-3 joint is slow.(3)The simulated hysteretic curve is in good agreement with the test,and the crack initiation and propagation process is basically consistent with the test phenomenon,which shows that the subroutine used in this paper can better predict the crack initiation and propagation process of the joint.