Effect of moisture content on the flexural properties and dynamic modulus of elasticity of dimension chestnut timber

Abstract

Moisture content (MC) has an important influence on the physical and mechanical properties of wood. This has to be taken into account when using timber for structural purposes; in particular, a correct estimation of the modulus of elasticity (E) is not only important for the key role that this parameter plays in design calculations, but also because it is a property that can be measured non-destructively and used to predict the quality of the material and, thus, to strength grade it. Hence, moisture content adjustment factors between MC 12 % and green state for density, static and stress vibration dynamic E were developed based on linear constant percentage model for dimension chestnut timber. The experiment was conducted on 200 ungraded pieces of 80 × 80 m2 cross section. For density, the adjustment suggested by the European standard EN 384 is appropriate below fibre saturation point (FSP), however, a more suitable equation is reported for pieces above FSP. Concerning E, the recommendation of EN 384 results in an overestimation, when the adjustment is applied to pieces with MC between 12 and 18 %, and an underestimation if applied to green timber. An appropriate adjustment equation is suggested for chestnut timber, taking into account the proper balance between accuracy and simplicity in the model usage and the desirable safety when performing an MC adjustment for structural use. An increment of 27.7 % in bending strength from green to dry state was also calculated. Finally, the feasibility of strength grading of chestnut green timber was investigated, concluding that the same efficiency can be expected if the grading is performed on dry or on freshly cut timber.