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Textiles are widely used in tensile structures due to their low weight, flexibility, and ability to span large areas efficiently through membrane action. Weft-knitted textiles, in particular, offer customization at a unit level, enabling the creation of locally programmable, 3D-shaped, continuous membranes. However, their mechanical characterization remains challenging, despite its importance for structural applications such as flexible formwork. This study examines the biaxial elastic properties of CNC weft-knitted textiles, focusing on the influence of knit architecture on their mechanical response. A custom biaxial tensile testing setup was developed to test three knitting patterns – interlock, tuck, and hexagonal – under three strain ratios (1:2, 1:1, and 2:1). Results show that stiffness varies significantly with knitting pattern and direction, reflecting asymmetries in textile microstructure. Strain distribution was also found to be non-uniform, with lower strains at the core than on the edges, highlighting the role of boundary conditions. Beyond providing insights into weft-knitted textile behaviour, this study contributes to an experimental framework for biaxial stiffness evaluation. The methodology serves as a proof-of-concept framework for the biaxial testing, test preparation, and result interpretation for knitted textiles, as well as for developing low-cost biaxial testing setups. These findings are particularly relevant for architectural and construction applications, where understanding the mechanical behaviour of knitted textiles is essential for structural integrity and design optimization.
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Textiles are widely used in tensile structures due to their low weight, flexibility, and ability to span large areas efficiently through membrane action. Weft-knitted textiles, in particular, offer customization at a unit level, enabling the creation of locally programmable, 3D-shaped, continuous membranes. However, their mechanical characterization remains challenging, despite its importance for structural applications such as flexible formwork. This study examines the biaxial elastic properties of CNC weft-knitted textiles, focusing on the influence of knit architecture on their mechanical response. A custom biaxial tensile testing setup was developed to test three knitting patterns – interlock, tuck, and hexagonal – under three strain ratios (1:2, 1:1, and 2:1). Results show that stiffness varies significantly with knitting pattern and direction, reflecting asymmetries in textile microstructure. Strain distribution was also found to be non-uniform, with lower strains at the core than on the edges, highlighting the role of boundary conditions. Beyond providing insights into weft-knitted textile behaviour, this study contributes to an experimental framework for biaxial stiffness evaluation. The methodology serves as a proof-of-concept framework for the biaxial testing, test preparation, and result interpretation for knitted textiles, as well as for developing low-cost biaxial testing setups. These findings are particularly relevant for architectural and construction applications, where understanding the mechanical behaviour of knitted textiles is essential for structural integrity and design optimization.
Computational design and fabrication of a pedestrian bridge using robotic shotcrete on a 3D-Knitted formwork
Journal article(2023)
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Philipp Rennen, Stefan Gantner, Gido Dielemans, Lazlo Bleker, N. Christidi, Robin Dörrie, Majid Hojjat, Inka Mai, Mariana Popescu, More authors...
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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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.
