Inventory-constrained design of a variable small diameter round timber structure

To improve the overall supply of renewable building materials, forestry industries around the world are seeking better ways to yield structural timber products from low diameter logs. Such logs are produced in large volumes, from both plantation thinnings and as the crowns of harvested saw log. However, they are marginally valued for use in conventional structures due to their small diameter, high dimensional tapering, and relatively low recovery volume and structural capacity when milled into sawn boards. This paper investigates the design of an optimised branched timber structure that utilises minimally processed round logs in their near-to natural dimensions, using a digital form-finding tool that combines the dual processes of Inventory-Constrained Design and Combinatorial Equilibrium modelling (CEM). A material inventory was generated directly from small diameter logs harvested from a plantation, giving a unique series of member lengths with associated diminishing diameters. The CEM model was used to optimise the geometric assignment of the inventory in a branched column structure, that also inherently benefits from members with diminishing diameter. This geometry was then developed into a proposition for a full scale branched column structure, with proof-of-concept design and prototyping of the intersecting geometry at the connection nodes undertaken. The development of this optimisation tool and the prototyping of the nodes, demonstrates feasibility for a novel application of this marginally valued forest resource that reduces material waste within the forestry and wood product value chains.