Advances in free-form Reciprocal Structures: Computational Tools for Design and Fabrication

The principle of reciprocity has been known since antiquity, and albeit their application as domes, slabs and bridges has been investigated and witnessed already by the work of Leonardo Da Vinci in Folio 899 of the Codex Atlanticus. (figure 1), their presence in realized buildings has been somehow limited and sparse. Nevertheless, reciprocal structures have sparked a renewed interest among professionals and researchers due to the unique design opportunities that they offer when combined with the use of computational form finding tools. From a didactic standpoint, they challenge the traditional sequence of form definition, structural dimensioning and detailing, as the shape cannot be defined a priori, rather is the result of continuous and iterative negotiations between the designer’s intention, the detailing and the structural dimensioning.
The Reciprocalizer is a plugin for Grasshopper – the parametric interface for McNeel´s Rhinoceros 3D - developed by the author to solve in real-time the geometry of reciprocal structures based on parameters controlling the way bars meet in each joint. In doing so, it effectively embeds the tectonic of construction within the geometrical solver, and renders the constructive detail an active element in the design process. It was developed within the Performance Aided/Assisted Design (PAD) framework, applied at the master in Architecture and Design at Aalborg University, with the aim of investigating the potential in integrating considerations on material, detailing, construction early in the design process. The Reciprocalizer is a paradigmatic example of the "embedded tectonics" factor in the PAD framework, since in reciprocal structures the constructional aspects cannot be detached from the geometry, since the joint specification determines the global geometry of the configuration.