JOURNAL PUBLICATION: Three cooperative robotic fabrication methods for the scaffold-free construction of a masonry arch

Geometrically complex masonry structures (e.g., arches, domes, vaults) are traditionally built with scaffolding or
falsework to provide stability during construction. The process of building such structures can potentially be
improved through the use of multiple robots working together in a cooperative assembly framework. Here a
robot is envisioned as both a placement and external support agent during fabrication – the unfinished structure
is supported in such a way that scaffolding is not required. The goal of this paper is to present and validate the
efficacy of three cooperative fabrication approaches using two or three robots, for the scaffold-free construction
of a stable masonry arch from which a medium-span vault is built. A simplified numerical method to represent a masonry structure is first presented and validated to analyze systems composed of discrete volumetric elements.

This method is then used to evaluate the effect of the three cooperative robotic fabrication strategies on the
stability performance of the central arch. The sequential method and cantilever method, which utilize two robotic
arms, are shown to be viable methods, but have challenges related to scalability and robustness. By adding a
third robotic agent, it becomes possible to determine a structurally optimal fabrication sequence through a multi objective optimization process. The optimized three robot method is shown to significantly improve the structural
behavior over all fabrication steps. The modeling approaches presented in this paper are broadly formulated and
widely applicable for the analysis of cooperative robotic fabrication sequences for the construction of masonry
structures across scales.