X-Form 3.0 | Constructing topologically optimized spatial structure using innovative mortise-and-tenon joints

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BACKGROUND Topology optimisation has emerged as a powerful method for generating structurally efficient architectural forms, particularly through algorithms such as Bi-directional Evolutionary Structural Optimisation (BESO). However, its application in architecture remains largely confined to digital design environments or additive manufacturing processes, with significant challenges in translating optimised geometries into buildable systems due to fabrication constraints, transportation limitations, and construction complexity. In parallel, traditional timber construction systems—such as mortise-and-tenon joinery—offer highly efficient, reversible, and materially intelligent assembly logic, yet are rarely integrated with contemporary computational design workflows. This project addresses this gap by developing a hybrid design-to-construction framework that bridges topology optimisation, traditional timber tectonics, and digitally enabled fabrication.

CONTRIBUTION X-Form 3.0 is a design-led research project developed for the IASS 2023 Design Competition and Expo (Integration of Design and Fabrication), and exhibited at RMIT Design Hub. As project lead, Dr Nic Bao co-developed the research with Xin Yan, Congcong Ren, and Prof. Yi Min ‘Mike’ Xie, establishing an integrated computational and fabrication workflow that links topology optimisation, material system design, and on-site assembly. The project introduces a multi-volume constraint BESO (MV-BESO) method to generate slender, tree-like structural systems aligned with load paths, while embedding fabrication constraints derived from carpentry logics. The optimised structure is discretised into modular timber components for subtractive manufacturing, and assembled using a series of traditional mortise-and-tenon joints, including plugging, connecting, and steering joints. A hybrid construction workflow is developed, combining robotic milling, CNC fabrication, and augmented reality (AR)-assisted assembly, enabling efficient prefabrication, transportation, and on-site construction. The system demonstrates high material efficiency, structural performance, and constructability. The project establishes a novel integration of computational optimisation, traditional tectonic intelligence, and digital construction technologies.

SIGNIFICANCE The project was awarded Third Prize in the IASS 2023 Design Competition on Innovative Lightweight Structures, and selected for exhibition in the IASS 2023 Design Competition and Expo: Integration of Design and Fabrication, organised by the IASS Working Group 21 (Advanced Manufacturing and Materials), and held at RMIT Design Hub. The competition and exhibition brought together leading architects, engineers, designers, and researchers from around the world to showcase cutting-edge lightweight structural systems. The project was evaluated by an international jury including Sigrid Adriaenssens, Ruy Pauletti, Arno Pronk, and John Orr, demonstrating high-level peer recognition within the global structural and computational design community. The research contributes to advancing performance-driven design, digital fabrication, and sustainable timber construction by establishing a viable pathway for translating topology optimisation into buildable architectural systems. By integrating traditional joinery with computational design and AR-assisted construction, the project proposes a scalable methodology for lightweight, modular, and resource-efficient structures. The work was further disseminated through presentation at the 63rd Anniversary Symposium of the International Association for Shell and Spatial Structures (IASS 2023) at Melbourne Convention & Exhibition Centre , strengthening its academic impact and positioning it at the intersection of research, design innovation, and construction practice. This project bridges digital design, material systems, and construction processes, positioning architecture as an interface between computational intelligence and fabrication-aware tectonics.