Anisotropic material behaviour under compression of Eucalyptus nitens with high moisture content

The safety of timber compression members of bridges and piers when submerged in or exposed to water is of major concern because the stiffness and strength of wood decline when moisture contents increase. Plantation-grown Eucalyptus nitens has predominantly been harvested for its wood fibre. In this study, compression experiments were undertaken with a Universal Testing Machine to examine the suitability of this species as a structural material. In particular, the anisotropic material behaviour at moisture contents (MC) above its fibre saturation point (FSP) was investigated. Experimental and theoretical analyses showed that stiffness and strength were dependent on MC and loading direction, while the failure mode depended mainly on the loading direction. There was a transformation from the “softening” behaviour in compression parallel to the grain to “hardening” behaviour in compression perpendicular to the grain below and above the FSP. The moisture reduction factor of strength from fully water-saturated state (mean MC = 66.9 %) to dry (MC = 12 %) was between 0.55 and 0.60 at the mean and 5th percentile strength level. The results suggest that compressive behaviour of plantation-grown E. nitens is highly anisotropic for a broad MC range. Design guidelines for using E. nitens in fully water-saturated applications can be established.