In-place and prefabricated connections.

The newly available opportunities to digitally design, simulate, and fabricate individually unique pieces calls into question the modern approach of standardization of components and its complementary ubiquitous joining solutions.

A significant challenge in building free-form geometries in stone arises from the required accuracy of the joining techniques to accommodate a large number of unique voussoirs.

This research proposes an assembly strategy for free-form stone shells that relies on a local joining solution at each step of the assembly sequence. Integrating structural analysis with the ability of robots to perform custom non-repetitive stone carving and the ability of cast metal to be formed with great geometric flexibility, the methodology aims to minimize the use of wasteful scaffolding while allowing the adjustable fitting of the resultant voussoirs.

The approach incorporates a 5-step process from design to assembly: At each stage of the simulated assembly sequence, finite element analysis is performed to define the exact location, direction, and size of the joint needed to stabilize each unique voussoir through tension, compression, bending, or shear. The joint geometry is then optimized to take local forces and is machined to a 1.5mm tolerance with a robotic arm. The assembly is executed by rings following a specific assembly sequence, registering each piece with a custom adjustable drift pin. This process accommodates the precision needed at each stage of the assembly, allowing deeper or shallower registration in each course and permitting pieces to move and correct until all pieces are fitted in place. The final joint is cast in-situ with a low melting point metal, fixing the pieces to their final position.

The final results show the specialized assembly joint at each step of the assembly sequence. Two marble prototypes serve as a proof-of-concept of the methodology and suggest that the integration of structural evaluation with an adjustable assembly approach enabled by robotic fabrication can reduce the need for scaffolding in the construction of free-form shell structures.