Analytical model of twist in Norway spruce (Picea abies) timber

Abstract This paper presents an analytical model for twist in timber. The model is based on calculating the twist in cylindrical shells and combining these shells to create timber studs. The shells will deform when the moisture content changes, owing to tangential shrinkage perpendicular to the fibre direction and longitudinal shrinkage parallel to the fibre direction. If the fibre direction is not parallel to the shell direction, this will cause twist in the shell. The twist in each shell contributes to the twist in the stud. The model has been used for a parametric study to determine theoretically the influence of parameters such as sawing pattern, stud size, spiral grain angle variation and tangential and longitudinal shrinkage. The model has also been used to predict the twist in 196 studs of Norway spruce timber. The model was able to predict 67% of the variation in twist among these studs.

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