EN 338 Strength Characterization and Grading of Four Less-used Timber Species Grown in Nigeria for Structural Uses

Abstract

In Nigeria recently, less-used timber species have been introduced into the main stream of timber markets, as a relief for over-exploitation of well-known species that are going into extinction due to over-exploitation for construction purposes. This study successfully classified four timber species grown in Nigeria into different strength classes in accordance with EN338, such as Ako-(Brachystegia eurycoma), Ara-(Pterocarpus erinarceus), Obobo-(Guarea cedrata) and Epuu-(Ricinodendron heudelotii) timber species. These timbers were obtained from famous timber market in Ibadan, southwestern Nigeria. All timber specimens used for physical and mechanical tests were prepared and tested in accordance with EN 13183-1 and EN 408 for structural timber. Four- point bending test was used for determining the bending strength and modulus of elasticity of each specimen using Universal Testing Machine. Characteristic values of the bending strength, modulus of elasticity and density were determined. The average moisture content of Ako, Ara, Obobo and Epuu were 11.78, 12.71, 23 and 24 %, respectively. Timber classification was conducted after properties values adjusted to 12 % moisture content as specified by EN 384. For density, Ako had the highest of 747.26 kg/m³ density followed by Ara and Obobo and Epuu had the lowest density of 481.71 and 477.15 kg/m³ and also assigned to strength classes D 50, D 24, D 18 and C 16 respectively, in accordance with EN 338.