Structural design is a search for the best trade-off between multiple architecture, engineering, and construction objectives, not only mechanical efficiency or construction rationality. Producing hybrid designs from single-objective optimal designs to explore multi-objective trade-offs is common in the design of structural forms, constrained to a single parametric design space. However, producing topological hybrids offers a more complex challenge, as a combinatorial problem that is not encoded as a finite set of real numbers but as an unbonded series of grammar rules. This paper presents a strategy for the generation of hybrid designs of quad-mesh pattern topologies for surface structures. Based on a quad-mesh grammar, an algebra is introduced to measure the distance between designs, find their similar features, and enumerate designs with different degrees of topological similarity. Structural design applications are shown to highlight the use of topologically hybrid designs as a surrogate for obtaining multi-objective trade-offs.

Several structural systems rely on a specific hierarchy between their constitutive elements, which results in topological constraints on the feasible patterns that can describe them. Folded, corrugated, or creased surface structures require this bipartition, also called two-colouring, between independent wavy and smooth directions. Finding a valid pattern for complex design problems is not straightforward and identifying relevant ones is important as creasing can either strengthen or weaken a structure. This paper presents a way of tackling such a design problem, by focusing on the roof of the Great Courtyard of the British Museum, revisiting this structure with a creased shell to increase its bending stiffness in the key directions. The methodology includes two-colour topology finding of corrugated patterns, parametric structural analysis, and simple structural optimisation through data analysis for topological combination, which opens new research avenues for performance-informed topological exploration.

This paper presents a formwork system consisting of a bending-active gridshell that simultaneously serves as falsework and integrated reinforcement for realising a ribbed funicular concrete skeleton shell. Encased by a knitted textile shuttering, the formwork system was demonstrated through KnitNervi, an architectural-scale, funnel-shaped demonstrator measuring 9 m in diameter and 3.3 m in height. The gridshell is materialised from straight steel rebar actively bent into curvilinear, double-layered rebar cages. Regular stirrups and pairs of inclined stirrups forming triangulated shear connectors provide the necessary shape control and stiffness for the load-bearing falsework. The rebar cages define the shape of the concrete ribs by supporting a knitted closed sectional mould and stay in place to structurally reinforce the resulting ribs. The focus of this paper lies on the falsework and reinforcement system with its interrelated design drivers. The geometric design includes the funicular form finding of the target shell with Thrust Network Analysis and the incremental form finding of the bending-active gridshell with its informed assembly sequence towards the funicular target with Finite Element Analysis. The engineering of the falsework demonstrates its sufficient load-bearing capacity and deflection control to support the weight of the wet concrete at an architectural scale. Sensitivity studies reveal the effectiveness of activating the double layer through the shear-connecting stirrups, the relevance of the internal connection design, and the geometric integrity during a potential stepwise casting sequence. The construction of the demonstrator verified the shape control and fabrication design. In only 36 h, the bespoke falsework gridshell was efficiently assembled from its kit-of-parts of standard rebar elements with adequate precision, logistics, time, and material resources. It was relatively lightweight, compact for transport, and employed low-tech construction techniques common to the rebar industry. Its structural geometry and informed bending-active logic enabled its efficient construction without digital fabrication or wasteful, costly moulds, which typically present the bottleneck for custom concrete structures. The resulting funicular concrete skeleton shell saves structural mass, hence embodied carbon, compared to unarticulated bending-dominant typologies. The overarching motivation of the research is to outline a strategy that could mitigate the environmental impact of the construction sector, applicable to a broad range of technological contexts.

Facing the challenges of our environmental crisis, the AEC sector must significantly lower its carbon footprint and use of first-use resources. A specific target is the reduction of the amount of concrete used. Funicular structures that base their strength on their structurally-informed geometry allow for material efficiency. However, a bottleneck for their construction lies in their costly and wasteful formworks and complex reinforcement placement. This research presents an alternative flexible formwork system consisting of a bending-active gridshell falsework and fabric shuttering for ribbed funicular concrete shells. The falsework becomes structurally integrated as reinforcement and is designed as two connected layers offering shape control and sufficient stiffness to support the wet-concrete load. The paper focuses on the development of a design-to-fabrication workflow and a graph-based data structure for gridshell falsework and reinforcement in the computational framework COMPAS. The implementation utilises, customises and creates packages for the form finding of the ribbed shell with TNA and the gridshell with FEA. The research is based on a demonstrator realised in the context of the Technoscape exhibition at the Maxxi Museum in Rome, Italy. The computational workflow was used to design this system and translate it for materialisation. The demonstrator serves as proof-of-concept for the novel material-efficient construction system. Its key to efficiency lies in the structurally-informed geometry for both the formwork and the resulting ribbed concrete shell.