Design process for prototype concrete shells using a hybrid cable-net and fabric formwork

• Review of flexible formwork systems for anticlastic shell structures.
• Workflow for the design and optimization of a shell shape and its flexible formwork.
• Design and construction of a prototype shell to validate the overall approach.
• Formulation of design criteria for the cable net and its topology.
• Strategy for calculation of prestresses before and after casting.

This paper sets out to explore the potential of combining a cable net with a fabric, in particular to scale the concept of flexible formworks to the size of large-span roofs and bridges, especially when applying a thin coat of concrete or mortar to form a shell structure. By carefully designing the cable net and its topology, and calculating and controlling the prestressing forces, it is possible to form a wide range of anticlastic shapes, beyond those of the hyperbolic paraboloid.A complete workflow for the computational design of a shell shape and its corresponding flexible formwork are presented as a proof-of-concept for future work. Two prototype shell structures were built based on this workflow to validate the overall approach, to compare the built geometry with that of the design model and to identify further challenges when developing and scaling up the concept. In addition, a comprehensive overview of flexible formworks for anticlastic shells is presented to frame the present research.