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Introduction

Contemporary research in architecture, favoured by the use of advanced computational tool-sets, has focused on the integration of material properties within the digital design environment in order to inform physically consistent architectural design. This approach enables the designer to embed complex material characteristics and behaviours as an active agent in the making of architecture (Menges 2012) and allows the exploration of non-standard building materials and techniques. The industrial needs for standardized production processes have selected just a limited number of techniques considered appropriate to satisfy the criterias for mass production. With the implementation of custom-based digital workflows, antique craft-based techniques can be revisited and reinterpreted under the perspective of “digital crafting”, attempting at defining a novel relationship between material behaviors and human activities, mediated through the use of computational tools, working on innovative interpretations of old processes, performance and language towards their implementation in architecture (Oxman 2007; Thomsen and Tamke 2014).

The technique of weaving has been widely acknowledged as one of the most antique surviving crafts, carbon dated to between 10,000 and 12,000 years old (Wikipedia, Basket Weaving). A woven artifact can be considered the result of a mediation between material and humans, between raw products of a territory and the cultural knowledge of craftsmanship. A sort of manual material computation is indeed implemented while working with the raw material. Through a direct engagement with matter, weavers perform an immediate problem-solving procedure, as every knot they make constrains the next weaving step (Muslimin 2010).

One of the main reasons why the weaving technique for construction of walls has been abandoned is the high level of permeability that it exhibits (Muslimin 2010). In the research, outlined in this paper, this feature has been re-considered and implemented in the design of a proto-tectonic semi-permeable partitioning system.

The research focused on the creation of an architectural weaving system in which form, structure and material are coherently developed and integrated as in biological formations (Hensel et al 2010; Oxman 2010), taking advantage of the intrinsic mechanical properties of the technique. The research attempts at answering three main questions. First, how can an antique crafting technique be implemented towards the creation of a novel architectural system as mediation between digital control and manual crafting? Second, how can we accurately compute the complex behaviour of weaving patterns and inform it with performative criteria? Third, how can we mediate between the high precision of digital fabrication tools and processes, and the imperfections inherent to natural materials?

Methodological Procedures

The research is carried out in three main phases: the choice, analysis and parameterization of the material system, a design process which capitalise on the material logics analysed, and a fabrication phase, where a prototype is constructed as a proof of concept of the developed research.

Phase One: Definition of the material system. Initial analysis are made to define the most appropriate materials for weaving at the scale of architecture. Technically, weaving is defined as a process of construction by interlacing or interweaving strips or strands of pliable material. Focusing on natural materials, different species of Willow (Salix) and Rattan have been analyzed in order to determine the most appropriate towards the realization of a full scale architectural system. Several families of willow are studied according to their geometrical characteristics and elastic behavior, together with different mechanical tests and FEM analysis. A strict correlation between stick typology and weaving pattern does exist as the choice of the material section naturally reduces the range of pattern variation.

Parametrization of the material system. Consequently, the experiment focuses on testing the bending behavior of a typical rattan stick and modelling its variable geometrical configurations within the digital environment, understanding its physical behavior and the best way to develop it in the software. An accurate simulation of the bending behaviour is obtained through the use of Kangaroo for Grasshopper/Rhinoceros, a well known add-on which embeds physical behaviour directly in the 3D modelling environment. Kangaroo is essentially a Particle-Spring System used for form-finding. Rattan sticks bend elastically within specific limits, which vary in proportion with the level of hydration. This behavior is instrumentally measured determining the minimum elastic bending radius.

Phase two: Design development. Embedding the physical behaviors of the chosen material system, the research focused on the design of a proto-tectonic weaving system, expression of a coherent collaboration between material, structure and form, and the realization of a full scale prototype. The research seeks to extend the limits of traditional weaving crafting by pre-computing its configuration and anticipating its morphological and assembly characteristics. A fundamental aspect of the experiment is the creation of a lightweight self-standing system, capable to partition interior spaces and provide a differential screening experience, to mediate environmental light conditions and user experience. This is instrumental to the development of a low-tech construction system able to connect antique cultural crafting with digital manufacturing and following partially DIY logics due to the easily mountable structure. The design process is developed parametrically within Grasshopper interpreting this structural scheme and embedding the material features following several steps.Shifting from baskets to architecture involves a change of scale, requiring the reconsideration of the weaving technique in its dimensional and force parameters, which cannot be linearly scaled. The structural resistance of traditional weaving is based on a combination of bending resistance and friction between interwoven elements. A fundamental role in the design of the weaving system is played by the vertical warp elements. For architectural purposes, the original are completely rethought, to create a stable and performative system. A second aspect in the development of a weaving structure, is to study the pattern generated by the wefts along the surfaces, managing the curvature of the rattan sticks where they intersect with vertical elements, allowing both for mechanical and visual filtering control.This is instrumental to the development of a low-tech construction system able to connect antique cultural crafting with digital manufacturing and following partially DIY logics due to the easily mountable structure.

Step three: Weaving Enclosure fabrication. A final prototype  is designed and realized as proof of the concept for the design workflow and to test the physical implementation of the construction system. The prototype is realized in a hybrid fabrication set, where the plywood warp elements are produced via digital fabrication and the rattan strands are manually assembled.

Results

Different results emerge from the proposed methodology. Investigating the material system, highlights that willow sticks present several limitations such as insufficient length and non-constant cross-section, together with the fact that the section typically has an inner core and irregularities that do not allow an accurate computer simulation of its bending behavior. Differently, commercial rattan is generally stronger and presents an even distribution of vascular bundles over the stem. For the purpose of the research a circular “rod” stick section had been favoured over a plated one. Weaving patterns base their mechanical properties on the frictional and bending resistance generated by the interlacing sticks. The physical and digital testing, in terms of algorithmic description, determines the choice of the Strike & Strand pattern typology, which exhibits good and constant mechanical resistance.

In the design phase, a methodology for the generation of  lightweight weaving structures is developed. Starting from an overall sinuous surface, which is statically stable, a set of poplar plywood warp elements defines by the discretization of the initial surface and serve as vertical support for the structure. A script allows to parametrically-control a system of holes on the vertical warp defining a stable and accurate structural system based on frictional resistance. This not only allowing to precisely program where wefts are passing, but also generating even stronger friction than traditional weaving, mediating with material constraints such as maximum length and bending resistance. The control over the holes disposition can also be tuned according to extrinsic performative criteria, in particular to generate a field with differential screening ratios.

A fabrication protocol is developed and processed through an industrial 3-axis CNC milling machine. Several fabrication constraints, such as dimensions of the working areas and rubber suction cups to hold the plywood sheets during cutting operations, are embedded in the original design of the warp elements. An optimized .cnc format G-CODE was generated from Grasshopper to directly provide the machines with pre-processed working trajectories.

Discussion

Speculative research in material computation have promoted a new material awareness empowered by the advancements in computing and digital manufacturing. This paper argues that new approaches to material expressivity and performance can be applied to re-discover antique crafting technique and evolve them into novel construction systems. Through this approach, a proto-tectonic partitioning system has been developed proving the high integration between performance and aesthetics, between the absolute precision of the digital process of design and fabrication, and the implicit imperfection of handcrafts and natural materials. The adopted approach opens interesting perspective for the development of computationally assisted low-tech systems in architecture.