| The space grid structure is a structural form widely used in construction engineering in recent years,with reasonable force and outstanding shape.With the rapid development of domestic construction industrialization,traditional joints can not fully meet the requirements of industrial assembly,and the assembled single-layer grid structure with assembled joints becomes a major trend.The main contents and conclusions are as follows:Applying the assembled double-ring joint developed by our research group,a single-layer grid structure of 14m×14m assembled double-ring joint and free-form surface is designed.The surface shape of the structure is optimized by the free-form surface shape optimization method considering the influence of initial geometric defects.The joint system is optimized according to the mechanical properties of the assembled double-ring joint and the meshing of the structure.According to the similarity theory,the test model is obtained by 1/4scale of the original structure.The mechanical properties of the scale model are analyzed and compared with the original structure.The results show that the mechanical indicators of the test model satisfies the similar relationship with the corresponding physical parameters of the original structure,and the test model can objectively and truly reflect the mechanical properties of the original structure.The whole 3D model is established by Rhino to determine the spatial positioning of the structure,and to solve the two difficult problems of rod positioning and adjustment mechanism,and the three-dimensional modeling process of assembled single-layer grid structure is given.Considering the characteristics of assembled single-layer grid structure,the model installation scheme of trial firstly and assembly secondly is adopted.The"hammer excitation+vibration pick-up"scheme is used to test the damping characteristics,and the half power bandwidth method is used to calculate the structural damping ratio.The results show that there is no significant difference in the corresponding damping ratio of the same vibration mode,and the higher the order of the structural vibration mode is,the smaller the corresponding damping ratio is;the distribution of the natural frequencies of each order of the structure is dense,and the contribution of higher modes to the structural response is greater;the first mode of vibration of the structure is the whole Z-direction vibration,while the other modes are the local vibration.The natural frequencies of structures measured by damping characteristic test,and the damping ratio of the first natural frequency is about 0.545%.The static test uses full-span uniform load to track the load-displacement curve of assembled single-layer grid structures.The instability mode is that the structure is depressed at two diagonal corners,and then the bolt breaks at one diagonal corners,with the structure collapsing there and transitioning to the other diagonal until the entire structure collapses.The ultimate bearing capacity of the structure is 9.15kN/m~2,and the maximum vertical displacement is about 1/282 of the span when the structure is unstable.The finite element model of single-layer grid structure with assembled double-ring is established by space beam element-virtual spring element method,in which the simplified joint stiffness of double-ring joint is introduced,and the finite element analysis software ANSYS is used to analyze the structure.The results show that the mode of structural instability is local instability.The ultimate bearing capacity and initial stiffness of the structure are about 66%of that of the rigid-jointed structure.Comparing the numerical simulation results with the experimental results,the mechanical properties of the finite element simulation are in good agreement with the experimental values,which verifies the effectiveness of the numerical method. |
