Research On Biaxial Loading Of Welded Hollow Spherical Joint Based On Q460 High Strength Steel

There are more and more high-strength steel large-span space structure projects,in which high-strength steel members are intertwined,the joints are dense and the stress state is complex.At present,there is no relevant research on the welded joints of high-strength space structure,especially the design proposal considering the multi-direction stress performance of high-strength welded joints.Therefore,this paper chooses welded hollow spherical joints which are widely used in large-span space structures as the research object.Based on the steel micro-damage fracture prediction model,the mechanical properties and damage mechanism of Q460 high-strength steel welded hollow spherical joints under biaxial loading are systematically studied in order to provide scientific basis for the further development of large-span space structures.The practical work is as follows:(1)Six full-scale models of Q460 high strength steel welded hollow spherical joints were tested under biaxial loading.The mechanical properties of welded hollow spherical joints were compared and analyzed from the aspects of test phenomena,failure mechanism,load-displacement curve,ductility coefficient,fracture load and displacement,ultimate bearing capacity,etc.The test results show that the ultimate bearing capacity of the main pipe under tension is higher than that of the main pipe under compression,and the two-way compression is the most disadvantageous condition.The direction of branch force has little effect on ductility coefficient of welded hollow spherical joints under tension condition,but has significant effect on ductility coefficient of welded hollow spherical joints under compression condition.The ductility coefficient of the main and branch pipe forces under different working conditions is larger than that under the same working conditions,and the ductility coefficient of the specimen increases obviously with the increase of the pressure value of the main and branch pipe.(2)Finite element refinement models considering welding seam,heat-affected zone and the negative tolerance of steel plate were established by FEM software ABAQUS,and the influence of mesh size on the calculation results was discussed.Based on the SWDM microscopic fracture prediction theory,the fracture load and displacement of the specimen were checked.The test results show that the bearing capacity of the main pipe under biaxial compression is the smallest,which is the most disadvantageous condition.The two-way tension load-carrying capacity of the main pipe under tension is relatively small,which is the most disadvantageous condition.The direction of branch force(tension or compression)has little effect on ductility 'coefficient of welded hollow spherical joints under tension,but has significant effect on ductility coefficient of welded hollow spherical joints under compression.With the increase of branch pressure,the ductility coefficient of the specimen increases obviously.(3)A large number of numerical examples are given to analyze the influencing factors of the bidirectional mechanical properties of welded hollow spherical joints.The effects of the parameters such as outer diameter of hollow spherical joints,wall thickness of hollow spherical joints,outer diameter of steel pipes,thickness t of steel pipes,angle between main and branch pipes,and axial force ratio of main and branch pipes on the mechanical properties of welded hollow spherical joints under bidirection.The results of parameter analysis show that the ultimate bearing capacity of joints decreases with the increase of outer diameter of hollow sphere and axial force ratio of main branch pipe,increases linearly with the increase of wall thickness of hollow sphere,and increases with the increase of outer diameter of steel tube,thickness of steel tube and angle of main branch pipe.The bearing capacity design formulas of joints under biaxial loads are presented.(4)The failure mechanism of welded hollow spherical joints under bidirectional loading is determined:the main pipe is elastic-plastic buckling failure under compression,and the main pipe is strength failure under tension.