Integral Mechanical Attachment for Timber Folded Plate Structures

Timber Folded Plate Structures combine the advantages of timber as a construction material, such as its carbon-dioxide storage, low energy production and favorable weight-to-strength ratio, with the structural efficiency and elegance of folded surface structures. The construction of such surface-active structure systems with timber is a relatively new development, driven by an increasing awareness for sustainable building constructions, and enabled by new engineered wood products. However, these constructions require a large amount of edgewise joints between the thin timber plates, which are difficult to address with state-of-the-art connection techniques.

Instead of using mass-produced mechanical fasteners for these connections, this thesis investigates the use of customized Integral Mechanical Attachment techniques, which use geometrical features of the parts to establish connections, rather than additional fasteners.

Integral joints were common in traditional woodworking, but their manual crafting became infeasible during the industrialization. However, new computer-controlled fabrication technology, which is already available in the timber prefabrication industry, allows for an efficient, automatic production of integral joints. The advantages of such joints have already been demonstrated in framing constructions, where timber beams are used as the primary structural components. The proliferation of automatic joinery machines has repatriated customizable single-degree-of-freedom (1DOF) joints, which allow for the fast and precise assembly of prefabricated components. The objective of this thesis is to transfer these advantages to the construction of timber folded plate structures.

Inspiration is taken from traditional cabinetmaking joints from Europe and Asia, as well as other industry sectors, where mass-produced integral joints are commonly used. The thesis will demonstrate several adaptations, which have been made for the application of the joints on cross-laminated wood panels, for their automatic fabrication and for the customized purposes in the jointing timber folded plate structures. The geometry, fabrication and assembly of these new joints is being implemented and tested through the development of algorithmic tools. This is followed up by a verification of the proposed methods through large- and small-scale physical prototypes.

In its three peer-reviewed core chapters, the thesis presents investigations ranging from an initial hybrid approach, where integral joints are combined with adhesive bonding, towards a completely integral mechanical attachment solution. After a first application of the joints on a surface, which is folded in one direction, the integral attachment of bi-directionally folded surfaces will be demonstrated. This is achieved through a new technique, which allows for the simultaneous jointing of multiple non-parallel edges, with single-degree-of-freedom joints.

Algorithms will be presented, which allow for the automatic processing and the automatic fabrication of the joints. The automation of these processes will then be used for the construction of a doubly curved, bi-directionally-folded surface, which obtains its structurally beneficial double-curvature through incremental changes in the geometry of the plates. Such geometrical variations had already been suggested in previous studies, but both the assembly and the fabrication of doubly curved folded surface structures, through a large amount of geometrically individual parts, rely on the automatic processing of geometry and fabrication data, which is introduced in this thesis.