ABSTRACT
In this research work, a reliability analysis was carried on three Nigerian timber specie namely: Mitragyna ciliata (Abura), Afromosia elata (Afromosia) and Confusa grandiflora (Berlinia) after classifying the species to international strength classification system using EN 338 (2003) with the aid of statistical package Easyfit (2010) .This was done after establishing the physical and mechanical properties in the laboratory using ASTM D193 (2000) and EN408 (2003). Mitragyna ciliata was assigned to strength Class of C18 with minimum characteristic values of density, strength and stiffness properties of 466 kg/m2, 80.2 N/mm2 and 9.21 kN/mm2 respectively as contained in EN 338 (2003). Afromosia elata and Confusa grandiflora were assigned to strength Class D30 with characteristic properties of density, strength and stiffness of 480 kg/m2, 131.2 N/mm2 and 11.85 kN/mm2 for Afromosia elata and 462 kg/m3, 89.2N/mm2, 12.74 kN/mm2 for Confusa grandiflora. The reliability analysis carried on the slender timber column was undertaken to check for six failure modes namely: compression, bending, flexural buckling, lateral torsional buckling, and carrying capacity of dowel connection and shear stress capacity of the joint failure modes. Critical mode of failure from the first four failure modes was found to be lateral torsional buckling mode of failure with the lowest β-value of 2.87 for Mitragyna ciliata, 3.4 for Afromosia elata and 3.52 for Confusa grandiflora, at a load ratio of 0.8 for compression and bending failure , 0.2 for flexural and lateral torsional buckling failure modes. Critical values of safety index obtained are lower than the code value of 3.8 (BS EN 1990:2002). While, the critical mode of failure for dowel connection was found to be in the carrying capacity of Dowel, with safety value of 1.69 at a load ratio of 0.8, also lower than the code value of 3.8 (BS EN 1990:2002).