DESIGN OPTIMIZATION METHOD OF RIGID NODES IN SINGLE-LAYER GRIDSHELLS

The nodes in single-layer gridshells transmit axial forces and moments along two axes simultaneously. Therefore, the nodes in single-layer gridshells, which bear a complex combination of forces and moments, should have reasonable configurations and excellent mechanical performances as rigid connections. Moreover, because of the difficulty of assembling of the gridshell high above the ground and the complexity of the gridshell's configuration, the connections between nodes and members should be reliable, convenient and applicable to any situation. This paper proposes a design optimization method of rigid nodes in single-layer gridshells. The end piece of the node is firstly configured so that a bar can be connected to the node easily. Subsequently, topology optimization is carried out upon the node core to explore highly-efficient configurations. In the optimization model, the rotational stiffness of the node is represented by a set of self-equilibrium moments which are irrelevant to loads, and thus the optimal nodes can transmit moments from any direction. Applying the force directly upon the design domain will cause some problems, such as the stress singularity and limitations for the topology optimization to explore other potential configurations. To solve this key problem, an inertia action, which is generated by applying an acceleration field, is applied to be equivalent to the concentrated force. With this equivalence, reliable and stable optimal results are obtained which are insensitive to the boundary conditions. Finally, a real-life node is designed and optimized as an example. The analysis of the connection of the optimal node to tube members and the analysis of mechanical performances of the optimal nodes are conducted. And the optimal node is compared with the traditional node. The analyses and comparison verify the proposed design optimization method, which combines the design of connection and topology optimization.