Inventory constrained design of a timber funicular structure
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Inventory constrained design of a timber funicular structure Kim R. Baber1 · Jane R. Burry2 · Canhui Chen2 · Joseph M. Gattas3 · Aurimas Bukauskas4 Received: 2 December 2019 / Accepted: 7 August 2020 © Springer Nature Switzerland AG 2020
Abstract This research investigates the development of a digital form finding model that combines the generation of funicular geometry with a material inventory constraint. The model provides a flexible design tool that facilitates exploration of structural form whilst simultaneously satisfying two rationalizing criteria. It maintains an equilibrated structure derived from funicular geometry; and optimises the assignment of a unique inventory of timber members having natural dimensional variation. The combined goal for the design outcome is to achieve material efficiency through both structurally rational form and minimization of material waste. The material chosen for the inventory is utility-grade sawn timber, being lightweight but with high levels of naturally occurring structural variability. Sawn timber boards that are rejected for structural applications due to frequent structural defects (knots, checks, splits etc.) represent up to 50% of the sawn product produced by Australian sawmills, and are destined for under-valued non-structural use, chipping or burning. Yet these boards can readily yield usable short length structural members, once defects are removed. In doing so, the process creates a unique inventory of random short members. These short members are well suited to articulated structures, which, by employing an inverted funicular geometry, only incur axial stresses and can employ simple (non-moment resisting) timber connections. This form finding tool and a first prototype pavilion are proofs of concept for viable structural application of what is otherwise a significant source of waste in the timber industry. Keywords Inventory-constrained design · Form finding · Funicular modelling · Timber structures
1 Introduction 1.1 Utility‑grade timber and inventory‑constrained design There is considerable natural variation in the properties of trees harvested as feedstock for sawmills. This variation exists between plantation stands, between trees within the same stand, and within the tree itself, so the resultant distribution of defects within sawn timber is highly unpredictable and can only be evaluated after sawn board production. As a result, a large volume of boards
are rendered uncertifiable for structural use, due to poor structural properties and/or a high incidence of natural defects. Ultimately, only about 50% of the volume of timber harvested will end up being certified for use as structural grade timber [1], shown in Fig. 1a–d, with remaining material sold as non-structural members, woodchipped to make particle based products, or burnt as fuel to power other operations in the sawmill plant. For those timber members containing frequent defects such as knots, checks, splits, and wane [2], defects can be cut out and the resultant lengths of timber may be cert
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