RELIABILITY-BASED INVESTIGATION ON THE COMPRESSIVE STRENGTH OF COMMONLY USED NIGERIAN TIMBER SPECIES
Keywords:Axial capacity, Compressive members, First Order Reliability Method, Nigerian-grown timber, Probability of failure, Reliability assessment.
AbstractThis paper considers the compressive strength both parallel and perpendicular to grain of not less than twenty Nigerian-grown timber species out of which, six commonly used ones were selected and their compressive resistance assessed under certain loads. First, it was found out that the basic compressive stress perpendicular to the grain of timber is about 22% of the basic compressive stress parallel to grain. A reliability assessment was then carried out using the First Order Reliability Method (FORM) to investigate the performance of a column section of 250 x 250mm and 300 x 300mm for the six Nigerian-grown timber species. Lophira alata was found to be the most reliable with a Probability of failure Pf = 2.78 x 10-3 and 7.1 x 10-2 under an axial load of 1000kN and 2000kN respectively. This was followed by Anogeissus leiocarpus with Pf = 2.53 x 10-2 and 5.26 x 10-3 under an axial load of 1000kN and 1500kN respectively. Others that followed were ‘Iroko’(Chlorophora excelsa),‘Abura’ (Mitragyna ciliata),‘Afara’ (Terminalia superba), and ‘Obeche’(Triplochiton scleroxylon), in the order of descending performance. It can been established from this study that, ‘Ekki’ (Lophira alata) and African birch (Anogeissus leiocarpus) could be suitable for bridge piles and piers, railways or related structures that require compressive members with high axial capacity whereas, ‘Abura’, ‘Obeche’, ‘Afara’ and ‘Abura’ would be best suitable for buildings.
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