Influence of Age on the Strength of Different Species of Timber

Abstract

Timbers are used as structural members in various areas of construction works. Hence the knowledge of properties of wood especially  strength and factors affecting the strength of timber is very important. This study was conducted to determine the effect of age on the  structural strength of timber. The wood species studied are Iroko (Chlorophora Excelsa), Nigerian Mahogany (Khaya Anthotheca) and Ita  (Celtis Mildbraedii). The age of timber were 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 the forest where fresh timber was  cut. The samples obtained were machined and trimmed to standard size with respect to BS 373 1957 (imprint 1999), 20mm X 20mm X  60mm for the determination of maximum compressive strength parallel to grain (MCS//), 20mm X 20mm X 20mm for static shear  strength and 20mm X 20mm X 300mm to determine the bending strength. The samples obtained were carried to the laboratory at Forestry Research Institutes of Nigeria (FRIN) in Ibadan for testing using Instron Tensiometer machine. SPSS was used to analyze the  relationship between strength and age of timber. The result obtained showed that the maximum compressive and Shear strength for  Iroko, were at 120years, whereas it has maximum bending strength at 70years. Nigeria Mahogany and Ita has maximum compressive,  bending and shear strength at 80 years, and 70 years respectively and among the three timber samples Ita is better in compression and  shear strength and iroko is better in bending strength. It was concluded that age of timber has significant influence on timber strength.