Concrete shell structures offer a mechanically efficient solution as a building floor system to reduce the environmental impact of our buildings. Although the curved geometry of shells can be an obstacle to their fabrication and implementation, digital fabrication and affordable robotics provide a means for the automation of their construction in a sustainable manner at an industrial scale. The applicability of such structures is demonstrated in this paper with the realisation of a large-scale concrete shell floor system, completed by columns, tie rods, and a levelled floor. The shell was prefabricated off-site in segments that can be transported and assembled on-site, and which can be disassembled to enable a circular economy of construction. This paper presents the conceptual and structural design; the automation of fabrication, thanks to an actuated, reconfigurable, reusable mould and a robotic concrete spraying process; the strategy and sequence of assembly and disassembly on-site using standard scaffold elements; and the sustainability assessment using life-cycle analysis. This prototype offers a reduction of about 50% of cradle-to-gate embodied carbon benchmarked against regular flat slabs before further improvement and optimisation.

The construction industry is responsible for nearly half of the UK’s carbon emissions, mainly due to the large amount of concrete used. Traditional formwork methods for concrete result in prismatic building elements with a constant cross-section, but the shear forces and bending moments that beams have to withstand are far from constant along their length. Up to 40% of the concrete in a typical beam could be removed. An iterative optimisation process has been implemented in a parametric modelling framework to generate and analyse optimal forms for non-prismatic beams that take into account the constraints imposed by the fabrication process, namely the use of fabric formwork. The aim of the resulting design tool is to facilitate the adoption of non-prismatic elements by the construction industry.