A significant portion of the environmental impact of a building’s superstructure lies in its structural flooring. By leveraging funicular forms such as thin concrete shells, a materially and carbon-efficient alternative to bending-active flooring systems can be attained. In addition, through segmentation and the use of dry jointed interfaces, a segmented concrete shell allows for ease of disassembly compatible with circular economy principles for the built environment. This paper presents a novel segmented concrete shell flooring system that leverages the symmetry of revolution of the classical fan vault form to facilitate future design flexibility through increased reconfigurability. The design and form-finding of the segmented fan concrete shell are detailed through the use of an evolutionary algorithm and finite element analysis. Quarter-scale prototypes were digitally fabricated using a robotic concrete spraying process which were then assembled and tested to assess its structural potential, evaluate the limitations, and identify areas of future work. An embodied carbon analysis demonstrates that the system provides a mass and embodied carbon saving compared to conventional flooring systems while adding approximately a 20% embodied carbon premium over a comparable non-reconfigurable segmented shell flooring system. Rephrased, the proposed system provides a positive embodied carbon saving if enabling design flexibility through reconfiguration increases the life-span of the system by at least 20%. Through this work, it is shown that a segmented fan concrete shell presents a viable lightweight and carbon-efficient flooring system which has the potential to become a sustainable alternative that enables disassembly, reuse, and even reconfigurability for circular construction provided further research and development to address its current limitations for adoption in industry practices.@en

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.

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The response of vaulted structures with dry-joints such as arches and shells can be predicted using graphical methods, limit state analysis, and rigid block analysis. However, these approaches assume material deformations are negligible. While acceptable for conventional masonry structures, there is a growing body of work investigating segmented vaulted structures where the segments comprise a large portion of the overall span. In such cases, material deformations and non-linearities can play a significant role. Typical analysis tools available are usually difficult to use and are not widely used by industry practitioners. In this paper, a modelling approach using a widely used finite element analysis package (LS-DYNA) is presented, using an ‘out-of-the-box’ approach for parameter tuning and modelling. This was then benchmarked against five experimental tests of dry-joint arches undergoing support displacements and a segmented concrete shell with large segments tested under a central point load. Crucially, the segmented shell exhibited imperfect dry-joints, with gaps occurring throughout various locations. A method of modelling and assessing such imperfections in a simple and practical manner is investigated through the use of a positive penetration allowance in the contact surfaces. The results show that the modelling approach is able to predict the collapse mechanism and failure support displacement for arches well, with further experimental tests required for 3D systems. It is envisioned that this work will add to the number of tools designers will have for analysing segmented vaulted structures with dry-joints.

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The fabrication of doubly curved concrete shells traditionally poses challenges in terms of material deposition and formwork manufacturing. Recent advances in digital fabrication techniques including robotics in construction have created tools to better tackle these challenges. We present a digital fabrication system to accurately deposit cementitious materials onto doubly curved surfaces using robotic concrete spraying in a process for prefabrication of structural shell components we call ARCS (Automated Robotic Concrete Spraying). Using inputs of a generic variable thickness shell volume, a robotic path is generated to deposit material onto the formwork surface where required. Paths are generated on the surface using geodesic lines as guides in order to create iso-curves for evenly spaced spray paths. Additionally, layers are incrementally deposited to allow for variable thicknesses across the surface. This approach is flexible enough such that additional features can be embedded onto the shell such as ribs. We demonstrate this automated fabrication process on a 1.8 m by 1.8 m scale shell specimen.

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