Emmanuel Appiah-Kubi, Charles K. Kankam and Kwaku Ansa-Asare
The exploitation of timber in Ghana and many parts of tropical Africa is limited to very few of the over 800 known species whose mechanical properties for structural use are unknown. The global demand for these few species with excellent properties in terms of their strength and quality of finishes has led to their over-exploitation and destruction of other less accepted species during logging operations. The structural use of timber is very limited in tropical Africa in spite of its abundance in the forests and its sustainability by cultivation. Considerable discussion has been held about the fuller utilization of tropical forests with particular reference to lesser-known species (LKS), but the problem has remained intractable and very little has been done. One main problem in promoting the LKS is lack of information on their realistic mechanical properties based on structural size dimensions. This paper reports results of research on the mechanical properties of four lesser-known species using structural sizes to assess their suitability as structural members. The species are Albizia ferruginea (Awiemfosamina), Sterculia rhinopetala (Wawabima), Blighia sapida (Akye) and Canarium schweinfurthii (Bediwonua). The results of study showed that Wawabima was the strongest whilst Bediwonua was the weakest in terms of their bending strength, density and modulus of elasticity. Wawabima had outstanding bending strength properties. With reference to standard codes, Wawabima compares very well with strength class D40, followed by Akye and Awiemfosamina with strength class D30 – both classes belonging to hardwoods. On the other hand, Bediwonua falling within strength class C24 belongs to softwood. The results indicate that Wawabima and Akye possess very good bending strength properties that are suitable for consideration in the design of medium to heavy structures. Awiemfosamina possesses good compressive strength but low bending strength, and together with Bediwonua are suitable for light structural members.
Mechanical Properties, Lesser - Known, Timber Species, Structural Us