Short-term and long-term bending properties of nail-laminated timber constructed of fast-grown plantation eucalypt

Abstract

Developing higher-value structural products from fast-growing eucalypt plantations - that are currently managed for woodchip production - can create new markets for these plantation resources and ensure a sustainable supply of timber for building construction. In this study, structural nail-laminated timber (NLT) panels with different span lengths were manufactured from a 16-year-old fast-grown Eucalyptus nitens plantation using a lamination system that can maximise the use of lower-grade boards in NLT production. The short-term bending performance in the elastic region and the effects of environmental conditions and structural grade of timber on long-term bending creep deflection of the panels were evaluated. The data analysis revealed that the current visual stress-grading method is incapable of estimating the actual modulus of elasticity (MOE) of the plantation Eucalyptus nitens timber. A linear regression model was proposed using the actual MOE of the boards that can predict the MOE of NLT panels with an average accuracy of 98%. The NLT panels made with higher-grade boards showed 22.4% greater MOE values than the NLT panels made with lower-grade boards. The lamination system used resulted in NLT panels with predictable and customised MOE with a remarkable average coefficient of variance of less than 2.6%. The long-term bending creep deflection of the test panels was significantly affected by daily variations in the relative humidity of the environment and structural grade of the timber used. The results of this study can be used in the development of an appropriate NLT production system from fast-grown plantation eucalypt.