Digital Inca: An Assembly Method for Free-Form Geometries

Abstract

Inca masons mastered a unique procedure of stone construction resulting in complex and precise configurations of visually zero-tolerance alignment. Each stone is nibbled away by a gradual transition of hammerstones from course to fine as the carving approaches a precise alignment on each edge at the visible face. Beyond this shared front edge, a gap opens to allow mortar to be packed in from behind for structural and setting purposes. These formations are limited to vertical walls as a result of the use of plumb technology. With so much current attention being focused on free-form geometries and procedural methods for masonry vaulting (Andriaenssens et al. 2014), this paper proposes a translation of the Inca wedge method into a digital process whereby stones align with each other to produce a global figure without the use of templating, falsework, or formwork. This differs from most conventional masonry processes whereby mortar is applied to units before positioning, allowing alignment to templates through the malleability of the mortar. Instead, units are dry fit to each other and then set in place. This inversion of the alignment procedure relies on precision carving of voussoirs to align with each other at specific moments in order to ensure proper self-assembly while simultaneously accepting mortar for setting. The resulting prototype shell structure is composed of uniquely carved voussoirs of autoclave-aerated concrete set with plaster in a similar manner to the Catalan and Guastavino methods. Previous research (Ramage 2006) has demonstrated the advantage of this lightweight material for vaulting purposes. The combination of this material property with the Inca assembly method results in an expedient assembly of complex shell structures. The potentials of this proof-of-concept suggests through results that future research can advance the intelligence of error aggregation through the aid of measuring, correcting, and carving throughout the assembly process just as the Incas constructed.