Recent development of powder-bed additive manufacturing promises to enable the production of architectural structures that combine high resolution and articulation with economies of scale. These capabilities can potentially be used for functionally graded metamaterials as part of the building envelope and structure, paving the way for new functionalities and performances. However, designing such multifunctional structures requires new design and modelling strategies to control, understand, and generate complex geometries and their transcalar interdependencies. The work presented here demonstrates a modeling framework that can unite multiple generative and organizational algorithms to create a unified, 3D printable building element that integrates a range of functional requirements. Our methods are based on an understanding of stigmergic principles for self-organization and developed to allow for a wide range of application scenarios and design intents. The framework is structured around a composite modeling environment based on a combination of volumetric modeling and particle-spring systems, and is developed to negotiate the large scalar range necessary for such applications. We present here a prototype demonstrator designed using this framework: Meristem Wall, a functionally integrated building envelope fabricated through a combination of powder bed 3D printing and CNC knitting.@en

Construction industry needs large volumes of materials and has a large carbon footprint. And although wind energy is renewable, the blades are hard to recycle leading to material waste. Our goal is to form a virtuous loop between these sectors by reusing wind turbine blades as construction elements. However, designing and building new structures from parts of existing ones raises novel design challenges in terms of geometry, structural properties and performance, processing and assembly. [...]@en

Digital fabrication technologies, such as 3D concrete printing, are currently making their way into the construction industry. The primary focus in this field is often on the depositing processes, such as extrusion 3D concrete printing, where material is typically applied in horizontal planar layers. This area has seen substantial progress in recent years. However, numerous research and development projects are specifically targeting the additive manufacturing of unreinforced raw concrete components. When implementing these technologies in practice, it has become clear that additional processes, such as fully automated process-parallel reinforcement integration, application of cover layers and formative and subtractive post-processing of the components, are essential for successful application. In addition, by varying the orientation, characteristics and arrangement of the layers, new shapes and functions can be realised. Examples include angled layer orientation for producing vaulted geometries without support structures, as well as non-planar layer formation for complex component geometries or assembly joints. Moreover, alternative innovative manufacturing processes, such as KnitCrete, Smart Dynamic Casting or Injection 3D Printing, reveal new potential for the application of digital manufacturing technologies in the construction industry. This article aims to demonstrate the possibilities offered by digital fabrication with concrete beyond the stacking of horizontal planar layers, and how these technologies can complement and expand a future digital fabrication strategy in the construction industry.

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The research project presented here aims to develop a design-informed manufacturing process for complex concrete shell structures in additive manufacturing and thus overcome limitations of traditional construction methods such as formwork- and labor intensity. To achieve this, an effort was made to merge the two technologies of CNC knitted stay-in-place formwork, known as KnitCrete, and robotically applied shotcrete, known as Shotcrete 3D Printing (SC3DP), and thereby reduce their respective limitations. The proposed workflow unites both digital fabrication methods into a seamless process that additionally integrates computational form finding, robotically applied fiber reinforcement, CNC post processing and geometric quality verification to ensure precision and efficiency. As part of a cross-university, research-based teaching format, this concept was implemented in the construction of a full-scale pedestrian bridge, which served as a demonstrator to evaluate the capabilities and limitations of the process. While overcoming some challenges during the process, the successful prove of concept shows a significant leap in digital fabrication of complex concrete geometry, reducing reliance on labor-intensive methods. The results shown in this paper make this fabrication approach a promising starting point for further developments in additive manufacturing in the construction sector.

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We are delighted to present you the special issue on Intelligent Construction and Automation as part of the Architecture, Structures and Construction journal. This issue covers a diverse range of topics related to the design, conception, and realisation of architectural structures and components, showcasing some of the latest developments in the broad field of Construction and Automation. The 10 papers collected over the past year focus on additive manufacturing (AM), robotic fabrication and assembly, computational design, and large-scale printing technologies. Process automation and 3D printing have been used to explore material and functional behaviour, design paradigms for AM, fabrication processes, and lightweight composite systems. Although Construction and Automation goes beyond 3D printing, these publications clearly demonstrate that additive manufacturing techniques currently hold a prominent place in the field. Moreover, with Artificial Intelligence (AI) gaining interest in the AEC industry, we expect it to appear prominently in future special issues of the Architecture, Structures and Construction journal.@en

Thin-walled textile-reinforced concrete beams have recently emerged as a promising approach for material-efficient design. However, the increased complexity of the formwork is a major challenge in implementing such elements for broader use in the construction industry. This study presents a novel type of stay-in-place flexible formworks with integrated textile reinforcement. The use of weft-knitted textiles allows the integration of continuous high-strength rovings as shear reinforcement and the introduction of spatial features within the fabric to guide bending-active rods to shape the complex cross-section geometry. The manufacturing procedure and the structural performance were investigated in an experimental campaign consisting of four concrete beams with I-profile cross sections tested in three-point bending, where aramid rovings were used for the shear and conventional deformed steel bars for the flexural reinforcement. The transverse reinforcement ratio proved to be essential in increasing the shear strength. Thereby, the use of digital image correlation measurements of the surface deformations allowed the direct assessment of the strains and, thus, the mechanical activation of the textile reinforcement. The full tensile capacity of all the aramid rovings crossing the governing crack could not be exploited due to the brittle material behavior, resulting in a progressive failure once the first roving reached its tensile strength. Compatibility-based stress fields were used to predict the load-deformation and failure behavior of the tested beams, which resulted in an excellent agreement of the ultimate loads and failure modes obtained from the model with the observations and results from the experiments.

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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.

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The higher complexity of adaptive façades with respect to conventional static façades hinders their applicability to the built environment. To address this, passive solutions aim at lowering the number of components while preserving the benefits of these systems. In this paper the design of a two-component passive dynamic sunshade that combines Shape Memory Alloys (SMAs) and knitted textile is presented. The novelty resides in the way the textile acts as an active member of the system, counteracting the SMA when in its martensitic (inactive) stage. The properties of the textile and design of the systems repeating movement are determined through mechanical testing. With nodal thermal modelling the main drivers of the SMA spring temperature have been studied. Results show that it is possible to achieve a promising range of movement with the proposed system, but both the textile and the spring could be more optimized to achieve a larger stroke. Results of the thermal analysis highlight that there is a need to concentrate the solar radiation on the spring for it to be independent from the outdoor temperature and work solely with solar radiation. Overall, the presented research expands the knowledge on the design of low-components-based passive sunshades and showcases an example of how textile can become an active member of the mechanical system.@en

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.

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This paper describes the structural design, digital fabrication and construction of KnitCandela, a free-form, concrete waffle shell with KnitCrete, a falsework-less formwork approach using a custom prefabricated knitted textile as multi-functional, structural shuttering layer and a form-found cable net as the main load-bearing formwork. The digitally designed and fabricated textile provided integrated features for inserting and guiding elements such as cables and inflatables that helped shape the sophisticated mould. With a total weight of only 55 kg, the 50 m² formwork was easy and compact to transport. On site, the formwork was tensioned into a timber and steel rig, the pockets were inflated, and then coated with a thin layer of custom-developed, fast-setting cement paste. This paste served as a first stiffening layer for the textile, minimising the formwork's deformations during further concrete application. Fibre-reinforced concrete was manually applied onto the formwork to realise a 3 cm-thick shell with 4 cm-deep rib stiffeners. The novel approach, for the first time applied at architectural scale in this project, enables the building of bespoke, doubly-curved geometries in concrete, with a fast construction time and minimal waste, while also reducing the cost and labour of manufacturing complex parts.

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This paper presents the design, engineering and digital fabrication strategies for a circular pedestrian bridge to be built as part of “De Groene Boog” development of the A16 highway north of Rotterdam, The Netherlands. The bridge is designed as a lightweight funicular unreinforced concrete gridshell with openings based on the principle of a three-hinged arch extrapolated to 3D geometry. In its realisation, it demonstrates a model of circular construction using recent material developments (such as recycled concrete) and an efficient flexible formwork system using knitted textiles. The presented design and fabrication process is developed collaboratively by the Block Research Group at ETH Zurich and De Groene Boog. The structure is commissioned by the Dutch Ministry of Infrastructure and Water Management (Rijkswaterstaat).@en

Conventional construction of doubly-curved concrete structures is a time-, labour- and cost-intensive process. Flexible formworks have already been identified as a possible solution to produce such structures more efficiently. The KnitCrete technology developed at ETH Zurich uses 3D weft-knitted fabrics as stay-in-place formwork, which deliver multiple advantages over woven textiles due to their wider range of feasible geometries and possibility to include features and local material properties. The textile is initially coated with a fast-setting high-strength cement paste. The stiffened membrane is stable enough to serve as formwork for the final concrete layer. This paper discusses potential reinforcing strategies to guarantee structural safety and serviceability in KnitCrete structures. Possible approaches range from the use of the textile as a stay-in-place formwork as well as final reinforcement (by utilising high-strength fibrous materials such as aramid, glass or carbon fibre) to the implementation of geometric features, such as channels within the textile to guide conventional reinforcement or post-tensioning tendons. The feasibility and efficiency of the proposed reinforcement strategies have to be experimentally verified, for which a systematic methodology is proposed. Preliminary analyses of the experimental campaign show the beneficial effect of the knitted reinforcement on the cracking behaviour of the textile-concrete composite material. Additional research is needed to exploit the potential of possible hybrid solutions using short steel fibres, post-tensioning or linear steel or glass fibre reinforcement.@en

A novel formwork system is presented as a material saving, labour reducing and cost-effective solution for the casting of bespoke doubly curved concrete geometries. The approach uses a custom knit technical textile as a lightweight stay-in-place formwork with integrated solutions for the insertion of additional elements, and is fabricated as a nearly seamless fabric. Using weft knitting as the textile formation technique minimises the need for cutting patterns, sewing, welding or gluing, when compared to conventional weaving and gives the possibility to integrate channels, openings, have varying widths and directional material properties, thus broadening the geometric design space. The system has been tested through a small-scale concrete footbridge prototype, built using a pre-stressed hybrid knitted textile and a bending-active structure that acted as a waste-free, stay-in-place, self-supporting formwork. Through the gradual buildup of strength in thin layers of concrete, formwork deformations during casting were minimised. This allowed for low tensioning levels of the fabric and the possibility to use higher pressure (e.g. during shotcreting) in applying the subsequent concrete without intermediate support from below. The computational design and fabrication of the knitted textile formwork included integrated channels for the insertion of bending-active rods, tensioning ribbons and features for controlling the concrete casting. The analysis and process of increasing the stiffness of the lightweight and flexible formwork is presented. The hybrid approach results in an ultra-lightweight formwork that is easily transportable and significantly reduces the need for falsework support and scaffolding, which has many advantages on the construction site.

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Knitting offers the possibility of creating 3D geometries, including non-developable surfaces, within a single piece of fabric without the necessity of tailoring or stitching. To create a CNC-knitted fabric, a knitting pattern is needed in the form of 2D line-by-line instructions. Currently, these knitting patterns are designed directly in 2D based on developed surfaces, primitives or rationalised schemes for non-developable geometries. Creating such patterns is time-consuming and very difficult for geometries not based on known primitives. This paper presents an approach for the automated generation of knitting patterns for a given 3D geometry. Starting from a 3D mesh, the user defines a knitting direction and the desired loop parameters corresponding to a given machine. The mesh geometry is contoured and subsequently sampled using the defined loop height. Based on the sampling of the contours the corresponding courses are generated and the so-called short-rows are included. The courses are then sampled with the defined loop width for creating the final topology. This is turned into a 2D knitting pattern in the form of squares representing loops course by course. The paper shows two examples of the approach applied to non-developable surfaces: a quarter sphere and a four-valent node.@en

This paper presents initial results of research focused on developing a novel type of formwork for concrete based on pre-stressed fabric formwork principles. It aims at creating geometries that are fabricated in one piece by knitting technical fibers, which could ultimately be used as reinforcement for concrete. This approach would result in a spatial textile that minimises the need for patterning, sewing, welding or gluing compared to a conventional approach to fabric formwork and textile reinforcement based on woven fabrics. It makes it possible to create directional material properties aligned to the internal force flow. This paper presents an overview of the proposed prefabrication technique and exemplifies its feasibility through small-scale experiments.@en