Ball State University
LOG KNOT is a robotically fabricated architectural installation which aims to expand and optimize the use of full trees and irregular timber geometries in construction. LOG KNOT creates an infinite singular and three-dimensionally bent loop of roundwood, borrowing strategies from traditional wood building and manufacturing. (1) Only about 35% of the wood of a tree is estimated to be used in construction (2), focusing mainly on the straight tree trunk and generally omitting smaller roundwood members altogether. By utilizing robotic fabrication processes and 3D scanning technology to create complex timber curvature that requires minimal formwork for assembly, this project aims to make better use of valuable timber construction resources, expanding on research projects such as the Wood Chip Barn (3) at Hooke Park (4), Limb at University of Michigan (5), or industry applications developed by companies such as Whole Tree Structures (6). The process and design methodology shared by these projects constitutes a paradigm shift in the design and construction of wood structures: rather than first mass-standardizing an irregular product (a tree) to subsequently mass-customize a design from the standardized components (plywood, 2x4s, etc.), each project starts with the available natural timber geometry working with, and capitalizing on its idiosyncrasies. This reciprocal design process fosters synergies and feedback between material, fabrication, digital form, and full-scale construction. In three sections, this paper will outline processes and methodologies for robotic fabrication, variable complex-curvature creation, joinery detailing, geometric and structural optimization, the reduction of moisture-related material failures, and on-site assembly. First, the research team developed a design method to create curvature from roundwood pieces, both regular and irregular. Components are computationally processed to form a spatially complex figure-eight knot (Savoy knot). Based on initial 3D models, a number of irregularly shaped trees and small roundwood members that cannot be processed by traditional sawmills are selected and harvested from a local forest. To complete the design process from form-to-log towards log-to-form, the trees are 3D scanned and the 3D model is adjusted to fit the available timber stock inventory. Second, the structure is computationally optimized and fabrication protocols are developed for the available robotic system, a KUKA KR200/2 with a 5hp CNC spindle. Custom computational solvers locally optimize the structure for bending and tension at each tri-fold mortise and tenon joint and custom fabrication protocols improve the positioning of a work piece in relation to the robotic end effector. Each wood component is treated with Pentacryl, a non-hygroscopic and non-toxic wood stabilizer, to prevent checking and shaking which can compromise connections. Third, a series of full-scale prototypes are constructed to develop connections and structural details, further improving the design and fabrication protocols. Due to the unique joint design, LOG KNOT requires only minimal formwork for assembly and can be built without heavy machinery. The main research contributions of this architectural installation are in the area of minimal formwork assembly, bending and tension force optimization of mortise and tenon joints, as well as variable 3D compound curvature creation for regular and irregular roundwood geometries.
(1) Blondeau, Etienne-Nicolas, and Honoré-Sébastien Vial Du Clairbois. Encyclopédie méthodique, marine. Vol. 160. Chez Panckoucke, 1783.
(2) Ramage, Burridge, Busse-Wicher, ereday, Reynolds, Shah, Wu et al. “The wood from the trees: The use of timber in construction.” In Renewable and Sustainable Energy Reviews 68 (2017): 333-359.
(3) Mollica, Zachary, and Martin Self. “Tree Fork Truss.” Advances in architectural geometry 2016 (2016): 138-153.
(4) Self, Martin. “Hooke Park: application for timber in its Natural Form”. In Advancing Wood Architecture: A Computational Approach. Edited by Menges, Schwinn, and Krieg, Routledge, 2016.
(5) Von Buelow, Torghabehi, Mankouche, and Vliet. “Combining parametric form generation and design exploration to produce a wooden reticulated shell using natural tree crotches.” In Proceedings of IASS Annual Symposia, vol. 2018, no. 20, pp. 1-8. International Association for Shell and Spatial Structures (IASS), 2018.
(6) “Research and Development,” WholeTrees, accessed June 18, 2019, https://www.google.com/policies/privacy/.https://wholetrees.com/technology/