Design and fabrication of innovative shell structures using topology optimisation and advanced manufacturing techniques
Creators: name: Ma, Jiaming
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400505
subject: Construction materials

description: Shell structures are used extensively in various industries and commonly exist in nature. Designing shell structures using conventional engineering techniques often leads to limited structural forms, low structural performance and high levels of material waste. In this thesis, several topology optimisation methods are developed to systematically investigate efficient shell structure layouts in nature and to design innovative and high-performance shell structures for engineering and architectural applications. Advanced manufacturing techniques are employed and effectively combined with the new design methods to produce intricate physical prototypes that serve as proof of concept.

This thesis is comprised of four interrelated research lines. The first research line emerges through the development of a transdisciplinary computational method that is used to optimise 3D free-form shell structures. Biomechanical mechanisms are integrated into the topology optimisation process, which considers both structural stiffness and nutrient transport. The optimisation mechanisms of leaf veins are then investigated through a combination of experimental measurements and numerical simulations. Following the above approaches, the topological details of computationally optimised leaves and three types of representative plant leaves are examined. Through comparisons between the numerical and experimental results, it is found that improving the efficiency of nutrient transport plays a critical role in the morphogenesis of leaf veins. Contrary to popular beliefs found in the literature, this study shows that structural performance is not a key factor in determining venation patterns. The topology optimisation method developed in this research line can be used directly to assess the computational morphogenesis of other shell structures in nature.

The second research line explores the creation of novel furniture by leveraging state-of-the-art techniques in topology optimisation and advanced manufacturing. A new workflow that augments the design and fabrication of highly efficient structures is proposed. Several novel pieces of furniture, including flat-pack designs, are produced using the new workflow and serve as proof of concept. The design and fabrication processes used to produce the novel furniture are simple, efficient and relatively low cost. Both additive and subtractive manufacturing techniques are used to create the prototypes. 

The third research line develops a constraint-mapping approach to the topology optimisation of ribbed slabs and shells. Using this approach with brick elements, the continuity of the ribs can be guaranteed for a classic slab model under distributed forces. The new approach can produce ribbed slabs with lower compliance than that achieved by a thickness control method using shell elements. The approach is successfully integrated into the solid isotropic material with penalisation (SIMP) method, the SIMP-based robust topology optimisation method and the bi-directional evolutionary structural optimisation method, respectively. A numerical example of a curved shell is provided to demonstrate the effectiveness of the approach. 

The final research line explores the redesign and reconstruction of a classical ribbed floor system using the proposed topology optimisation method and advanced hybrid manufacturing techniques. Compared to the famous historical design by Pier Luigi Nervi, which uses the isostatic line method, the ribbed slab generated by the new method offers a noticeably higher structural stiffness with the same amount of material. An innovative formwork created using robotic 3D printing and CNC machining is developed for construction. The formwork can be used to cast large-scale ribbed floor unit and is reusable and recyclable. The new ribbed slab and a column are cast using the proposed formwork and assembled as a proof of concept. This research line, from design to construction, provides a systematic means of producing ribbed floors in the digital era. 

Overall, this thesis contributes to the understanding of plant leaves as efficient shell structures in nature and offers new design and fabrication methods for creating innovative shell structures in engineering application. Main contributions of this thesis are outlined below. First, it reveals the critical role of nutrient transport in the morphogenesis of leaf veins through topology optimisation and experimental measurements, raising a different argument to that found in the literature. Second, it creates a new workflow and several pieces of novel furniture to demonstrate how topology optimisation and advanced manufacturing can be effectively combined to facilitate the design and production of innovative structures. Third, it improves on the topology optimisation of ribbed slabs and shells. Finally, it redesigns and reconstructs a classical ribbed floor system to demonstrate the power and potential of new digital design and fabrication techniques.