Bending and modulus of elasticity properties of ten Lesser-used timber species in Ghana using structural Dimensions

For structural use, the properties of large size specimens are preferred to those of small clear specimens because of unavoidable defects such as knots and shakes found in wood. The objective of this study was to assess the bending strength, modulus of elasticity properties and failure behaviour of ten Lesser-used Species (LUS) by use of structural size dimensions (50mm x 120 mm x 2000 mm). The ten species were Albizia ferruginea, (Gulland Perr) Beuth., Sterculia rhinopetala,(K. Schum), Blighia sapida,(Koenig), Canarium schweinfurthii (Engl.), Petersianthus macrocarpus, (P. Beauv.) Liben, Sterculia oblonga, (Mast.) Cola gigantea, (A.Chev.) Celtis zenkeri, (Engl.) Antiaris toxicaria (Lesch.) and Amphimas pterocarpoides (Harms.). The moisture contents of the 10 timber species used ranged from 16.1% (Antiaris toxicaria) to 51.0% (Albizia ferruginea). It was observed during loading under flexure that the elastic stiffness and rate of increase in the strength capacity of the beams did not change after three cycles of loading and unloading. All the beams failed in a form of tension rupture. The breaks were usually splintering tension failure or brittle (brashness) tension failure or a combination of the two modes
of failure. Sterculia rhinopetala exhibited the highest bending strength with a 5th percentile bending strength of 56.8 ,/mm2 and a mean local modulus of elasticity of 15,973 ,/mm2. Sterculia oblonga was also found to be the 2nd best in terms of material properties with a 5th percentile bending strength of 52.1 ,/mm2 and a mean local modulus of elasticity of 16,408 ,/mm2. Celtis zenkeri which had the highest mean local modulus of elasticity, however, had the 6th best 5th percentile bending strength of 39.9 ,/mm2. A good linear correlation (69.6-91.3%) was established between mechanical strength properties for average density, average bending strength, average local modulus of elasticity and average global modulus of elasticity.