Mechanical properties of South African timber for structural grading: a systematic review

This systematic literature review investigates studies that focused on the mechanical properties of South African (SA)-grown timber, with a focus on their relevance to structural grading. This review consolidates existing mechanical property studies of SA pine and Eucalyptus timber, aiming to evaluate consistency with structural grading systems and identify key data gaps. Eighteen studies that were conducted between 1978 and 2024 and reported characteristic values for SA pine and Eucalyptus grandis W.Hill ex Maiden were included. Data were extracted for all relevant strength properties used in structural timber design, together with sample sizes, coefficients of variation and whether the timber was graded. The results show that graded SA pine still meets the grade requirements defined in the 1980s. This suggests that its stiffness has remained stable over time, despite concerns that it may have declined. Eucalyptus grandis, despite outperforming SA pine in both strength and stiffness with less variation, is still not formally part of the structural timber grading system. No study tested the mature outerwood of eucalyptus in isolation, despite its importance for grading. Bending stiffness generally exhibits lower variability than bending strength within samples, suggesting that smaller sample sizes may be acceptable when stiffness is the only property of interest. The findings emphasise the need for continued in-grade testing using standardised testing methods, and the development of a grading system for E. grandis that represents its full potential.