Abstract:
In this investigation, 22 different species of Nigerian grown hardwood were sourced from different sawmills in the country, cut and planed in accordance with the specification of Reunion Internationale des Laboratoires et Experts des Materiaux (RILEM). Appropriate compression, tensile, and bending tests were conducted on a total of 396 test specimens at 132 test specimens for each of the indicated stress conditions. The results of the tests revealed areas of best application for each timber species. In particular, it was found that the green basic tensile strength of Ayo parallel to grain is the highest of all 22 tested species (39.5N/mm2) while Ayunre has the highest dry basic tensile strength parallel to grain (25.8N/mm2). Similarly, Ata has the greatest green basic bending strength parallel to grain, at 44.3N/mm2 while Ekki exhibited the strongest dry basic bending strength at 30.1N/mm2. Oro indicated the highest green basic compression strength at 30.5N/mm2 while Apa was the strongest by dry basic compression strength at 27.8N/mm2. A single factor analysis of variance (ANOVA) carried out on the strength results revealed that at 0.05 pre-set level of significance, the variances in the values of tension, compression and bending strengths for all timber species considered were significant. The obtained results suggest that there is a need to revisit the present strength grouping of Nigerian timbers as well as their grade stresses for groups of species. This is because strength groupings of timber as obtained in the present research do not fully agree with the groupings in the current Code (NCP 2:1973).
