Chestnut: from coppice to structural timber. The case study of "Uso Fiume" beams sampled in Liguria
Recently Agriculture Department of Liguria Region had supported studies and researches on the timber quality of living trees in local coppice chestnut forests, with the prospect to produce also timber for structural use. Under some ad-hoc funds a 30 years old coppice forest in the high Bormida Valley, never thinned after the last utilization, has been chosen for sampling. 18 selected trunks were felled and the assortment called “Uso Fiume” (UF) was chosen, getting 49 beams (cross-section from 12¥12 to 24¥24 cm), by way of saw-mill operations The UF-beam is a structural element, derived from Italian tradition. Such elements are used in Italian buildings over the time, in substitution to structural sawn timber, principally for roofing. The UF-beam is a square edged log with wane; more precisely it is a full log, edged on four sides, maintaining boxed heart and an approximately central pith. Today the features of such a beam is established according to the specific Italian standard UNI 11035-3 for spruce and fir and to the CUAP (Common Understanding of Assessment Procedure) n. 03.24/22 for chestnut and conifers. The beams were visually graded according to the Visual Strength Grading procedure and the physical and mechanical properties (density, modulus of elasticity-MOE and modulus of rupture- MOR) were determined according to the standard requirements (EN 408, EN 384, ISO 3131), disregarding the moisture content: the mechanical tests were performed with wood in green state (moisture content M.C.>30%) because it is the actual condition of use in building, due to the very low permeability of the chestnut heartwood which entails long seasoning time of large cross section beams. The study showed very high yields considering the stems-to-beams volume ratio, close to 70%. Characteristics values of the sample resulted: char. density kg/m³, char. modulus of elasticity E0,mean 10,3 GPa and char. bending strength fm,k 28,5 MPa. These results can be considered very promising because the data match the Strength Class D24 (EN 338), the same Class as full cross-section chestnut beams (at M.C.=12%).
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Copyright (c) 2013 Marco Togni, Alberto Cavalli, Davide Mannozzi
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