Classification of Finger Joint Timber Based on Strength Index

At present, off-cut wood pieces are dumped by sawmills as they are considered to be wastes in the wood industry. Inadequate length of sawn timber material is also reported to be a limiting factor for fully utilization of timbers. Finger joint, a method which connects two small pieces of timber together is identified as a sound technique to minimize the wastage. As there is no classification system applicable for finger joint timber in Sri Lanka, the present study focused on developing a classification system for selected 32 timber species based on their strength properties. The relationship between the strength properties and density of selected timber species was also investigated. Strength properties of finger jointed timber species were evaluated by three-point bending and compression tests according to BS 373:1957 using Universal Testing Machine (UTM-100).Factors were identified through an analysis to determine the strength index for the selected samples. The strength index values were grouped into five strength classes as very low, low, medium, high and very high. Cluster analysis was used in grouping the species with similar strength properties. Regression analysis was performed to identify the strength index of compression parallel to grain, compression perpendicular to grain, modulus of elasticity and modulus of rupture varies on density. A significant correlation (p=0.05) between the strength index and timber density was observed.