The mechanical properties of plantation Eucalyptus Nitens timber are currently assessed by applying visual stress grading (VSG) designed for the sawn timber from the mature plantation and do not represent the actual characteristics of the resource. However, the well-known limitation of VSG application for this resource led to the discovery of other methods to grade the timber to its relevant structural grade. There is potential for hardwood plantations in Australia to supply wood to the timber industry and be used in structural applications. However, it is necessary to employ criteria to evaluate the structural properties of this resource before it could be satisfactorily used for structural purposes. This research aimed to assess the use of non-destructive technique (NDT) through acoustic wave velocity (AWV), machine stress grading (MSG), and multiple linear regression (MLR) model to predict the modulus of elasticity (MOE) as a grade-determining factor. The results showed that there was a strong correlation (R² = 0.88) between the dynamic MOE (MOE_dyn) and static MOE (MOE_s) of the boards, proving the NDT as a reliable method for the MOE estimations of E. nitens timber. The results from the MLR model also showed that the density and AWV are effective parameters and their combination can be practical to estimate the MOE. There was a high correlation between the MOE obtained from MSG and MOE obtained from four-point bending, demonstrating that the MSG method through the flat-wise bending can be a suitable method for fast grading. The results also indicated that the measured MOE in the edgewise direction correlates with both the flatwise and longitudinal directions. The results also showed that the E. nitens timber resource has the potential to be used in structural applications with a wide range of MOE from 7 GPa to 21 GPa.

With the increasing availability of fast-growing Eucalyptus plantation logs in Australia in recent years, the timber manufacturing sector has become interested in discovering the opportunities of producing value-added timber products from this resource. Cross-laminated timber (CLT) could be a potential sustainable product recovered from this resource and supply material for commercial buildings. Shear of the inner cross-laminates, known as rolling shear, is one of the governing factors in serviceability and limit state design for this product under out-of-plane loading. This study evaluated the rolling shear (RS) properties of CLT with heterogonous layup configurations using different structural grade Eucalyptus nitens (E. nitens) timber under the planar shear test. Based on the results, G_r and ${\mathsf{\tau }}_{\mathrm{r}}$ values were shown to be significantly correlated with the density of the CLT panel. There was also a positive correlation between the RS modulus and MOR of the CLT panel. The specimens with high MOE in the top and bottom layers indicated the highest ${\mathsf{\tau }}_{\mathrm{r}}$ and F_max values. This indicated that using high-grade boards in the top and bottom lamellae plays an important role in increasing the RS strength, whereas using them in the cross-layer has a positive contribution in increasing shear modulus. The maximum observed RS strength and modulus ranged from 2.8–3.4 MPa and 54.3–67.9 MPa, respectively, exceeding the RS characteristic values of the resource. The results obtained in this study were comparable to those recommended in European standards for softwood CLT, demonstrating the potential use for eucalypt timber boards in CLT production. This paper provides an important insight into supporting the potential engineering applications of CLT panel products fabricated with eucalypt plantation.

Eucalyptus globulus and Eucalyptus nitens are the most dominant hardwood plantation species in Australia. Although containing a considerable amount of growth irregularities, there is an increasing interest by the industry in developing structural products, especially cross-laminated timber (CLT), from these plantation resources. In this study, for the first time, the rolling shear (RS) properties of CLT made of these two species were evaluated. Two groups of higher-grade and lower-grade CLT panels were fabricated from each species using polyurethane adhesive. The effects of the sawn-timber’ density in the cross-layer and the MOE of sawn timber in the top and bottom layers on the RS properties and failure modes of the CLT were then evaluated under three-point bending test. The results showed a positive correlation between the average MOE of the sawn timber in top and bottom layers and both GA_{eff (LB)} and τ value of the specimens from both species. The high-grade specimens from both species showed the highest shear stiffness and shear strength values compared to lower-grade ones. Furthermore, the RS values obtained were higher than those recommended in European standards for softwood CLT. These results provide useful information towards successful development of high-value CLT from the low-grade plantation eucalypts timber.