Reliability Assessment of the Nigerian Apa (Afzelia Bipindensis) Timber Bridge Beam Subjected to Bending and Deflection Under the Ultimate Limit State of Loading

摘要

Structural reliability analysis was carried out on the Nigerian grown Apa (Afzelia bipindensis) timber, to ascertain its structural performance as timber bridge beams. Two pieces of 50mm x 75mm x 3600mm of Nigerian grown Apa hardwood were bought, seasoned naturally and 80 pieces of test specimens were prepared for determination of their strength properties, (which include bending and tensile strengths parallel to grain) at a moisture content of 18%, in accordance with the British Standard BS 373 of 1957. Statistical analysis was carried out using the strength properties for determination of mean, standard deviation, coefficient of variations, confidence limits and Chi-Square goodness of fits. Structural analysis and design of a timber bridge beam using the determined data from the Nigerian Apa timber, in accordance with BS 5268 were carried out under the Ultimate Limit State of loading. Programme development for reliability assessment was written in FORTRAN programming language. Reliability analysis was carried out to ascertain its level of safety using First-Order Reliability Method (FORM). Sensitivity analysis was also carried out by varying the depth of beam, imposed live load, breadth of the beam, unit weight of the Apa timber, span of the beam as well as the end bearing length. The result revealed that the Nigerian grown Apa timber is a satisfactory structural material for timber bridge beams at depth of 400mm, breadth of 150mm and span of 5000mm under the ULSL. The probabilities of failure of the Nigerian Apa timber bridge beam in bending and deflection are 2.062×〖10〗^(-3) and 2.673×〖10〗^(-14) respectively, under the design conditions.