The influence of site and axial position in the tree on the density and strength properties of the wood of Pterygota macrocarpa (K.schum)

Static bending, compressive, shear and impact bending strengths and density of Pterygota macrocarpa (Kyere) were investigated using small clear wood specimens from three sites in the Moist Semi-Deciduous (North-West) forest type, Moist Semi-Deciduous (South-East forest type and the Dry Semi-Deciduous (fire zon) forest type The results show that height positions of samples in a stem significantly affected wood density, bending compressive, shear and impact strengths as well as modulus of elasticity. Wood density and mechanical properties decreased from the butt to the top of the stem indicating that wood samples from the crown area of a tree have lower strength properties. For example, mean densities of 670kg/m3, 640kg/m3 and 620kg/m3 were obtained for the butt, middle and top logs respectively and mean compressive strengths parallel to the grain of 66.12N/mm2, 59.46N/mm2 and 51.60N/mm2 were also obtained for the butt, middle and top logs respectively. The basic and grade stresses derived for the wood indicate that it may be classified to lie between structural strength classes SC5 and SC6 of BS 5756 (1980). The grade stresses for wood from the different height positions also indicate that they all lie between classes SC5 and SC6 of BS 5756 (1980) Density and mechanical properties of the wood of Kyere, with the exception of bending strength, also differed significantly with site. Wood samples collected from the site with the highest mean annual rainfall had the least density and strength properties. For example, whereas mean density of 630kg/m3 was obtained for samples from Amantia, mean density of 660kg/m3 and 640kg/m3 were obtained for samples from Akota and Abofour respectively. In the case of compressive strength parallel to the grain also, a mean value of 56.24N/mm3 was obtained for samples from Amantia whilst mean values of 60.68N/mm2 were obtained for samples from Akota and Abofour respectively.