Static- and fabrication-aware concrete shells segmented into flat tiles

Laccone F., Menicagli S.

Concrete shell  Digital fabrication  Conceptual design 

The design of freeform concrete shells has gained popularity recently, pushed by computational tools that allow manipulating and exploring complex shapes interactively. However, their actual fabrication, even on a small scale, still poses challenges of feasibility and cost. Continuous shells require accurate and dense formworks, while segmented shells offer a low prefabrication rate, especially in the case of variable curvature. We propose a novel structural concept for freeform shells, in which the shape is decomposed into flat tiles, touching each other at the midpoint of the edges. Once assembled, the tiles are post-tensioned to minimize the resulting tension on the structure under service load. The outer surface is finally completed with an in situ cast that fills the gaps and activates the entire shell behavior. The bottom surface presents a jagged aesthetic due to gaps and misalignments at the seams. We developed an automatic pipeline to manage the design process from a general input shape to fabrication. The input shape is segmented based on a field-aligned quad mesh computed from the principal stress of the thin shell. The flat tiles are obtained by extruding each face along the normal of the associated checkerboard mesh, i.e., a mesh whose 'solid' parts are the planar rhomboids with vertices on each quad edge's midpoint. The contact between adjacent tiles is ensured only at their edge midpoints so that forces can flow along the cross directions, namely the principal directions. Candidate post-tensioning paths are found by clustering the segments linking pairs of opposite midpoints of the tiles' edges. We discard paths that do not terminate on the boundary, closed loops, or paths with significant kinks, to avoid localized shear on the surface.

Source: fib International Symposium on Conceptual Design of Concrete Structures, pp. 175–175, Oslo, Norway, 29/06/2023 - 01/07/2023