Topology optimisation and additive manufacturing of structural nodes of gridshell structures

Gridshells, also called lattice shells or reticulated shells, are lightweight spatial structures. Their organic shape, column-free space, free-form surface and maximised transparency have provided limitless design freedom for architects and structural engineers. The design and manufacturing of structural connections (nodes) have been the bottle neck in the design and construction of gridshells, which is due to their complicated geometries and the three-dimensional loading conditions applying on these nodes. The invention of additive manufacturing (AM) provides the possibility of optimising the nodes by using topology optimisation (TO) algorithms. Instead of rationalising the geometry of the nodes to provide simplified connections for conventional production system, custom-designed connections can be achieved with lower weight and higher accuracy using combination of TO and AM. As a consequence, the optimised nodes help reduce the structure size and foundation requirements which leads to saving in the material cost. Furthermore, other features also make the newly designed nodes promising, such as the aesthetical features, high stiffness, high precision and less labour. In this study, Bi-directional Evolutionary Structural Optimisation (BESO) techniques are used to minimise the weight and the printing time required for each node. Firstly, the effect of general load cases on the optimised topology of structural node is studied by comparing the optimised results for the nodes under different individual load cases and combined load cases. Furthermore, the effect of the size of the design-domain on the final weight and topology of a node designed by BESO is examined by using different initial sizes. In addition, various smoothing methods for the final geometry are explored and compared with each other. The challenges of using AM in manufacturing nodes are also investigated through 3D printing individual optimised nodes and the optimised nodes for a case study of a prototype gridshell structure. Besides, comparisons made between optimised nodes and conventional nodes show the efficiency of the optimised nodes. An innovative experimental setup for quasi-static test of nodes under dominant design loads is also proposed in this study. Two nodes are designed and manufactured using BESO and AM to test by a test rig designed based on the proposed setup. In addition, a 3D finite element analysis is conducted, and the numerical model is validated against the test results