Effect of age on the structural strength of timbers commonly used in Nigeria

Abstract

Timber is a material used for structural purposes in construction. Hence, the knowledge of properties of timber especially strength and factor affecting the strength of timber is very important. Age of timber is one major factor affecting timber strength and timber was usually fetched without knowledge of whether the timber is matured to meet the structural strength required. Therefore, this research tends to evaluate the effect of age on the strength of some selected timber species so that forester and users likewise could be guided on when to deforest. In this study, timbers studied were Universitas Orientalis Kentuckiensis (Eku), Entandrophragma cylindricum (Sapele) and Gmelina Arborea (Melina). The age of timber was determined by counting the number of annual growth rings, which is the combination of early wood and late wood and samples of different ages of timber, were obtained by personal visit to forest where they were fetched freshly. The samples obtained were machined and trimmed to standard sizes according to BS 5268 pt2 2003. The compressive strength was done using a timber size of 20mm X 20mm X 60mm, 20mm X 20mm X 300mm for determination of the bending strength and shear was performed using 20mm X 20mm X 20mm timbers (all in three replicate). The maximum compressive strength values were 49.31kN/m² (at 45years), 45.89kN/m² (at 60years) and 11.30kN/m² (at 25years) for Eku, Sapele and Melina while the maximum bending strength were 187.55kN/m² (at 35years), 278.79kN/m² (at 70years) and 176.36kN/m² (at 20years) and shear strength were 10.05kN/m² (at 50years), 9.22kN/m² (at 70years) and 10.91kN/m² (at 25years) for the for the three samples. It was concluded that age of timber affects the strength of timber.