Development of a classification system for Sri Lankan timber species based on physical properties

Abstract

An investigation was carried out on selected twenty five Sri Lankan timber species to study different wood properties which are commonly applied in the timber industry in Sri Lanka. Wood density, modulus of rupture, modulus of elasticity, compression strength at rupture and compression in elastic limit at direction of parallel to grain were tested by five samples of each specimen at moisture content between 12% - 15%. The obtained results were analysed to find correlation among properties and to develop a classification based on the wood properties. BS 373:1957 (1999) standard was followed to test small clear samples in sample sizing, testing and calculation procedures. Three point bending test, compression parallel to grain test were applied to investigate mechanical properties and by measuring weight and volume at 12%-15% moisture content, density was calculated. Obtained results described a fair correlation among density and mechanical properties specially, modulus of rupture and modulus of elasticity. These results can be used to predict the mechanical properties with respect to density and vice versa. Above properties were referred to develop the classification into four basic grades as super grade, high grade, medium grade and low grade. Further any relationship could not be found between the timber classification published by State Timber Corporation and it proved that this classification is not based on the wood properties. It is recommended to extent the research by increasing types of properties, number of species and samples with various age limits and growing conditions and height of the trees. This could be benefitted to improve the effectiveness of the classification based on properties and to develop standards of the timber industry in Sri Lanka.