Structural properties of Irish-grown birch and use of non-destructive acoustic techniques for timber grading

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Abstract

The rising global demand for locally sourced resources and the push for more diverse forests have sparked a growing interest in broadleaved species as viable timber sources for construction applications. However, knowledge about the mechanical and physical properties of these species, specifically those grown in Ireland, is limited. This study investigates the structural performance of Irish-grown silver birch (Betula pendula Roth). The three properties that determine the structural grading of a species, namely modulus of elasticity, strength and density are examined. Additionally, knottiness, ring width, and slope of grain were measured. The trees used in this study were obtained from two plantations, aged 22 and 27 years. Logs from 26 trees were processed into sawn timber specimens, each measuring 2.25 m in length with a nominal cross-section of 75 × 35 mm2. The dataset achieved a yield above 90% of D18, which shows that Irish-grown birch can potentially contribute to the timber supply in Ireland. Non-destructive acoustic techniques were also examined on standing trees, logs, and sawn timber to identify the best quality material for producing structural timber. The strongest relationship with the mechanical properties was found in sawn timber. Measurements on standing trees had a stronger relationship with the structural quality of the sawn timber than with the log measurements. For segregation of trees and logs for the production of quality structural timber the study suggests the implementation of thresholds to exclude less promising material, potentially earmarked for other uses or left standing. Specifically, using the 15th percentile of the distribution of acoustic velocities measured at a site proves to be a practical compromise, balancing the supply of timber with high yields of graded timber.

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