Abstract
A batch of pine timber sawn from butt, middle and top logs was strength graded with the visual method (classification into grading classes KW—best quality, KS—medium quality, KG—inferior quality and Reject) and with the machine strength grading method—performed with the use of a mobile timber grader (classification into C strength classes). We compared the efficiency of grading classes and strength classes, depending on the type of log from which the material was obtained (butt, middle, top). Next, a strength grading machine was used to measure the modulus of elasticity in bending (MOE) and static bending strength (MOR). The ANOVA confirmed the influence of both the log type (butt, middle, top), the C strength class, and the visual strength grading class on the values of density (DEN) and MOR. Timber density and MOR decreased from the butt log section to the top log section. The ANOVA confirmed the influence of log type on MOE values, but only to a limited extent.
Highlights
Wood is a natural, ecological and renewable material with an isotropic structure and a wide range of applications
The use of wood in load-bearing applications in civil engineering requires the assessment of the mechanical properties of every single piece of timber used as a load bearing structural element
As a result of machine strength grading, coniferous timber is classified into C strength classes, whose characteristics have been specified in EN 338 [14]
Summary
Ecological and renewable material with an isotropic structure and a wide range of applications. Strength grading machines measure one or several wood properties that can be verified in a non-destructive way, and whose correlation with the wood’s bending strength is known These are the static or dynamic modulus of elasticity and the density of the timber under assessment. Visual strength grading of construction lumber consists of examining every piece of timber carefully and classifying it into the appropriate grading class on the basis of the visible defects of wood structure, shape and processing. The study presented here is aimed at developing and complementing the existing state of knowledge within the scope of influences on the efficiency of machine or visual strength grading, taking into account the type of log from which the timber under assessment was obtained (butt, middle, top). These research results may contribute to a more rational selection of round timber in terms of its anticipated structural applications
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