3D concrete has undergone significant developments over the last few decades but is rarely used for structural applications, as there are no standard commercial solutions for reinforcing 3D-printed load-bearing elements. The composites industry inspires this proposed concept which echoes Pier Luigi Nervi’s ferrocement of the last century. It uses 3D concrete printing (3DCP) and a patented technology called FBP for Flow-Based Pultrusion. Reinforcement is provided by long, aligned fibers, producing a transverse isotropic composite mortar. Initial experiments have demonstrated increased tensile strength and ductility, and an industrial device, in collaboration with XtreeE company, is currently under development. In this paper feasibility is shown through the design and the fabrication of an optimized thin shell demonstrator. The proposed methodology proposes a way to use this new anisotropic material to optimize the 2D design, via the geometry. Using a Tsai-Wu criteria, well-known for composite material design, it takes into account the different strengths in the various directions of the shell, and the different stress states induced by the various membranar and bending efforts due to external, distributed and concentrated loads.