5. 2
Interlocking folded plates—integral mechanical attachment for structural wood panels Christopher Robeller and Yves Weinand
Automatic joinery has become a common technique for the jointing of beams in timber framing and roofing. It has revived traditional, integral joinery, such as mortise-and-tenon connections. Just recent ly, the automatic fabrication of traditional c abinetmaking joints has been introduced for the assembly of timber panel shell structures. First prototypes have been assembled with such integrated joints for the alignment and assembly of components, while additional adhesive bonding was used for the load-bearing connection. However, glued joints cannot be assembled on site due to lack of controlled conditions, thus resulting in several design constraints. In this paper, we propose the use of dovetail joints without adhesive bonding in the case study of a timber folded-plate structure. Through their single-degree-of-freedom (1DOF) geometry, these joints block the relative movement of two parts in all but one direction. This presents the opportunity for an interlocking connection of plates, as well as a challenge for the assembly of folded-plate shells, where multiple, non-parallel edges per plate have to be jointed simultaneously.
Keywords integral
attachment, timber folded-plate structures, digital fabrication, design for assembly
200 Customized construction
1 Introduction Architectural designs are often inspired by folded shapes such as Japanese origami; however, folding principles like this can rarely be directly applied to building structures. Rather, many folded plates have been cast as concrete thinshells in the 1960s. These constructions were labor inten sive and required elaborate formwork for in-situ casting. Prefabricated constructions with discrete ele ments made from fiber-reinforced plastics were researched in the 1960s.1 Folded plates built from laminated timber panels were presented by Regina Schineis19 (Glulam) and Hans Ulrich Buri 2 as cross-laminated timber. These designs combine the elegant and efficient shape of folded plate shells with the advantages of structural timber panels, such as CO2 storage, and a favorable weight-to-strength ratio. However, a major challenge in the design of a tim ber folded plate is presented by the joints: Since timber panels cannot be folded, a large number of edgewise joints has to provide two main functions. One of these functions is the load-bearing behavior, where connector features of the joints have to provide sufficient stiffness and rigidity. The second main function of the joints is the assembly of the parts, where locator features of the joints are essen tial for the precise, fast positioning, and exact alignment of the parts. Benjamin Hahn 5 examined the structural behav ior of the first timber folded-plate shell, which was built from plywood and assembled with screwed miter joints. He concluded that the load-bearing performance could be improved significantly with a greater number of resistant connections. Inspiration for such improvements may be found in integral mechanical attachment techniques, the oldest known technique for the jointing of parts, where the geometry of the parts themselves blocks their relative movements.13 Such integrated joints have recently been rediscovered by the timber construction industry. Since 1985, mortise-and-tenon joints have not been used in t imberframe and roof constructions.7 Only very recently, integrated joints have also been proposed for the edge