| Bolt-ball joints are widely used in lattice and double-layer reticulated shells and are typical semi-rigid joints.In the traditional design and analysis,often ignore the node bending stiffness and the assumptions for the hinge node,in fact,the node is between just answer and articulated semi-rigid nodes,this assumption will result in actual structure internal force and skew the results of numerical calculation,nodes as net is one of the important components,its mechanical performance will affect the overall mechanical performance of a reticulated shell,it is necessary to study the mechanical properties of bolt ball node.In this paper,the real stiffness of bolted ball joints and its single layer cylindrical reticulated shells are studied,and the stability of bolted ball joints reticulated shells is compared with that of rigidly connected and hinged reticulated shells.The main work and conclusions are as follows:（1）by using the finite element software ANSYS and ABAQUS bolt ball node refinement model is set up,and get its bending rigidity,axial rigidity,axial compressive stiffness,bending stiffness and bending stiffness,Fan Feng etc by experimental results validate the rationality of the numerical simulation,and discuss the bolt ball node related parameters（bolt diameter,size,tail cone pretightening wall thickness and the thickness of the sleeve）and the influence of different tensile,bending stress ratio on its stiffness.The results show that the axial compression stiffness of bolt-ball joint increases with the increase of sleeve thickness and bolt diameter.The axial tension stiffness increases with the increase of bolt diameter and the thickness of cone head bottom plate.The critical preload of the bolt-ball joint is100 k N,and its flexural stiffness increases with the increase of bolt diameter.When the bolted ball joint is subjected to bending action,the ultimate bending moment decreases with the increase of bending stress ratio.Under the same stress ratio of tension bending and compression bending,the ultimate bending moment of bolt ball joint is higher than that of compression bending,and the initial stiffness does not change significantly.（2）the use of bolt ball node static performance parametric analysis and combined with the result of the node itself characteristic,based on three parameter power function model,consider the bolt pre-tightening force ball node size and thickness of the sleeve to the influence of the stiffness and prestressing force determined by regression analysis and the sleeve for bolt ball node initial stiffness and ultimate bending moment coefficient,the influence of bolt ball node bending moment-corner prediction formula.It has been proved that this equation can effectively predict the bending moment-angle curve of bolt-ball joint.（3）Low cyclic reciprocating load was applied to the numerical model of bolt-ball joints,and the hysteretic performance of the joints was analyzed through ductility coefficient,equivalent viscous damping coefficient,hysteretic curve and skeleton curve.The results show that the hysteresis curves of the bolt-ball joints are full spindle-shaped,the skeleton curves are typical "S" type,and the ductility coefficient and equivalent viscous damping coefficient are large,which indicates that the joints have good ductility,mechanical performance and energy dissipation performance.In the hysteresis curve,the ultimate bending moment of bolt-ball joint increases with the increase of bolt diameter,the ultimate bending moment of bolt-ball joint increases slightly with the increase of sleeve thickness,and the change of cone head bottom plate thickness has no significant effect on the ultimate turning Angle,energy dissipation capacity and ductility of the bolt-ball joint.（4）Considering the bending stiffness,axial stiffness and joint stiffness under the joint action of bending moment and axial force,a numerical model is established for bolt-ball joint single-layer cylindrical reticulated shell and its static stability is studied.The influence of span and span ratio of reticulated shell on the stability of bolted ball joint reticulated shell is discussed,and the stability bearing capacity of bolted ball joint reticulated shell,rigid connection and articulated reticulated shell is compared.The results show that the instability mode of the rigidly connected single-layer cylindrical reticulated shell is the depression of the top,and the initial stiffness and stability bearing capacity decrease with the increase of the span of the rigidly connected reticulated shell.In the semi-rigid reticulated shell with bending stiffness,the failure of the structure is characterized by jumping instability,and the top central rod is deformed along both sides of the span facing downward,and the instability presents a symmetrical distribution.There is no second critical point in the load-displacement curves of the semi-rigid connected reticulated shell considering axial stiffness and the reticulated shell considering bending and axial stiffness.When the reticulated shell is unstable,the top of the reticulated shell is depressed and deformed as a whole.When the hinged reticulated shell is unstable,its top center node has torsional deformation,and the whole reticulated shell presents torsional failure.Under different parameters of reticulated shells,the stability bearing capacity of rigidly reticulated shells is much greater than that of articulated and semi-rigidly reticulated shells.Among them,the initial stiffness and stability bearing capacity of articulated reticulated shells are the lowest,so it is not recommended to apply articulated joints to single layer cylindrical reticulated shells in practical engineering. |
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