Producing High-stiffness LVL from Eucalyptus fastigata: Part 3. LVL production and mechanical properties
By Doug Gaunt, Rosie Sargent, Armin Thumm, November 2021.
Download SWP-T135 (pdf)
Laminated veneer lumber (LVL) has been produced in a commercial radiata pine mill (JNL Wairarapa) using veneers from 23-year-old Eucalyptus fastigata. The veneers were glued using one of the glue formulations commercially used by the mill, to produce 24 LVL panels (1.2 x 2.4m), 40mm thick. Six of the panels were produced from veneers of known density and stiffness and the veneers for these were sorted to ensure the widest possible range of average stiffness values between these panels. The remaining panels were produced from veneers grouped according to their log-stiffness class (low, medium or high stiffness).
Mechanical testing of the LVL found that:
- With the exception of shear strength, the 95x40 E. fastigata LVL overall achieved the LVL 13 grade as limited by Bending Stiffness, with the other strength properties meeting or exceeding the highest LBL16 grade.
- Shear strength both on edge and on flat were very low.
- Poor glue spread was found to be an issue along with the showing a lot of splitting and fracturing along the, this issue needs further exploration.
- Further exploration using veneers cut from solid timber and then laminated to produce an LVL ‘similar’ product showed high shear strength. This suggests that the poor shear behaviour is a result of the processing conditions, rather than a characteristic of this species.
- Accurate measurement of veneer stiffness was found to be a very good predictor of final bending stiffness but not that reliable in predicting the strength properties.
- It is estimated that the LVL would produce 30% LVL16 and 70% LVL13. This compares with Radiata pine LVL commonly falling into LVL8, 10, 11 & 13 grades.
We recommend future work on this product focussing on understanding and mitigating the causes of poor shear behaviour. This to identify if improved processing with minimal handling, and no re-drying could reduce splitting in veneers, and improve shear properties.
No posts yet