Determination of Strength Classes of Selected Nigerian Timbers in Accordance with EN338 (2009)

Abstract

Wood has several unique, independent properties. The physical and mechanical properties of wood do vary from species to species and even within species due to environmental conditions during growth. In Nigeria, timber is been grade based on permissible stress (NCP) an upgrade to the limit state is required. A laboratory test was carried out to develop the physical and mechanical properties (four-point bending test) of the timber species in accordance with EN 13153-1, ASTM D143 and EN 408. The strength classification of selected timber was performed according to EN 338 using characteristic value of the material properties in accordance with EN384 from the generated physical and mechanical properties, after being adjusted to 12% (Eurocodes reference moisture content). The timber species considered were Tectona grandis and Gmelina arborea. The result showed Tectona grandis had a higher property than Gmelina arborea and the species were assigned to strength classes of D50 and D35 (hardwoods) respectively. The study shows that the selected timber species are suitable for structural purposes.Keywords: Strength classes, Nigerian timber, Four-point bending test, Tectona grandis, Gmelina arborea