Reliability studies on the Nigerian Ekki timber as bridge beam in bending under the ultimate limit state of loading

摘要

This paper provides the results of structural reliability analysis carried out on the Nigerian Ekki timber subjected to bending forces, to ascertain its structural performance as a timber bridge beam. Samples of the Nigerian Ekki timber were collected, seasoned naturally and their structural/strength properties were determined at a moisture content of 18%, in accordance with the British Standard BS 373, methods of testing small clear specimens of timber. Statistical analysis was carried out using the structural/strength properties determined. Structural analysis and design of a timber bridge beam using the Nigerian Ekki timber in accordance with BS 5268 were carried out under the ultimate limit state of loading. Reliability analysis of the Ekki timber bridge beam so designed to ascertain its level of safety was carried out using first-order reliability method (FORM). Sensitivity analysis was carried out by varying the depth of beam, imposed live load, breadth of the beam, unit weight of the timber, span of the beam as well as the end bearing length. The result revealed that the Nigerian Ekki timber is a satisfactory structural material for timber bridge beams at depth of 400 mm, breadth of 150 mm and span of 5000 to 7000 mm under the ultimate limit state of loading. Its probability of failure in bending under the specified operating conditions is 1.1 x 10-7, that is, one in ten million.