This paper presents Necto, a low-carbon CNC-knitted tensile membrane made from natural flax fibers and installed in the Corderie of the Arsenale at the 19th International Architecture Exhibition of the Venice Biennale. Suspended between four existing historic masonry columns and anchored to the floor at four additional points, the membrane forms a lightweight, form-active system within a protected heritage environment. Its functionally graded knit architecture aligns flax fiber inlays and density variations with the two principal stress directions, yielding a material-efficient and biodegradable structure. The structural design combines physics-based form-finding refined through the Force Density Method, nonlinear Finite Element Analysis for prestress calibration and boundary cable sizing under Eurocode-based load combinations, and detailed verification of all structural interfaces—including anchored ground supports, non-invasive clamped column supports with pressure-distributing layers, and a ring support that distributes the membrane stresses at the funnel over eight suspension cables. By treating form-finding, analysis, detailing, fabrication, and assembly as mutually informing constraints, Necto demonstrates how a multi-fidelity structural design process can deliver a full-scale CNC-knitted membrane within a protected heritage context.

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.