A Review of Mechanical Strength Properties of Some Selected Timbers in Nigeria

Abstract

The variation in mechanical properties of eight different timber species was reviewed from the project works on timber carried out in the Department of Civil Engineering, University of Ilorin. Kwara state, Nigeria. These species include Iroko (Chlorophora excelsa), Mahogany (Khaya ivorensis), Fanpalm (Borassus aethoiopum), Ekki (Lophira alata), Opepe (Nauclea diderrichii), Apa (Afzelia, bipindensis), Ayin (Anogeissus leiocarpus), Afara (Terminalia superba). The Annual Book of ASTM Standard Section 4, (D143), method of testing small clear specimens of timber was adopted to evaluate the variation of strength properties of the species from standard speed and dimension specifications. The strength properties reviewed were, compression parallel to grain, compression perpendicular to grain, static bending (flexure) and tensile strength parallel to grain. From the review, it was found that strength of timbers along the grain is far greater than across or perpendicular to grain showing the anisotropic nature of timber. Prior soaking of the specimen before test accounts for reduction in strength. Also deviations from the specified dimensions and speed of testing of specimen will in one way or the other affect the accuracy of strength obtained in the test. It is therefore recommended that strict adherence to the test procedure and specifications should be followed so as to achieve the exact strength values of timbers and that further research work be done on other timbers in order to maximize their usefulness as a construction material.