| The roof of Tianjin Yujiapu transport hub is single-layer reticulated shell structure, which has 144m north-south span, 81m east-west span and 25m vector height, and this structure is the largest span single-layer reticulated shell in China at present. The shell simulates shape and texture of conch, and its welded-box members distribute along spatial spirals. And this project has its own characteristics: shapes and dimensions of grids are different from each other; every joint has a different structure;each member bears complexly axial force, two-way shear forces, two-way moments.Cruciform diaphragm welded joint was used in this project ans it's the first time that this kind of joint is applied as connection system of a large-span single-layer reticulated shell structure. Cruciform diaphragm welded joint perfectly solved the technical difficulty "one joint one shape",and became another unique feature of this project.Aiming at this single-layer reticulated shell, its mechanical property is studied,and constraint condition and supporting scheme are investigated. Then structural stability of this shell is analysed, and effects of load distributions and constraint conditions on stability are investigated.Cruciform diaphragm welded joint has simple structure, but its application is very few. And there is no systematic analysis on bearing capacity and rigidity of this joint. Therefore, aiming at cruciform diaphragm welded joint, planar or spatial joints,symmetrical or asymmetrical joints are modeled in Ansys program, and failure mechanisms under axial force, out-of-plane bending moment, in-plane bending moment and torsion were studied respectively.Aiming at cruciform diaphragm welded joint, parametric FEM analysis is completed. Effect of various parameters on bearing capacity of joint was studied, such as section dimension of members, angle between members, thickness of joint plate and load type. According to the FEM results, calculation formulas of is bearing capacity of joint under axial force, out-of-plane bending moment, in-plane bending moment and complex loads were derived respectively.Typical joints including one cruciform diaphragm welded joint and two other complex joints were selected from this shell structure. And experimental studies under complex loads were conducted to obtain mechanical properties of typical joints.In order to ensure the feasibility and operability of the experiment, loads with 6 components are simplified and converted to 2 eccentric forces. And the load processing method is proved to be reasonable. The Ansys program was used to simulate the joint experiment. Different working states of the specimen joint were considered, respectively, and simulating procedure was gradually close to the actual test state. Experiment errors were also analysis.The effect of joint rigidity on stability behavior of the whole shell structure was investigated based on a simplified numerical method "double-element method". It was concluded that the joint rigidity has great influence on the buckling critical load, but not the buckling mode. In order to investigate influence of joint stiffness located in different parts of the structure, sensitivity analysis was conducted. It was concluded that influence of different parts on buckling load was different from with each other.Based on multi-scale modeling, natural vibration characteristics and dynamic responses were studied. Several typical joints were modeled with solid element. The results of the multi-scale model and raditional beam model were compared. It was concluded that solid joints can change stiffness distribution of the overall structure,and then change its dynamic characteristics. Solid joints have a low level of stress under frequent earthquake. |
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