Reliability Studies on Timber Data from Nigerian Grown Iroko Tree (<i>Chlorophora excelsa</i>) as Bridge Beam Material

Abstract

This paper provides the results of structural reliability analysis carried out on the data of Nigerian grown Iroko tree (Chlorophora excelsa), to ascertain its structural performance as timber bridge beams. Five pieces of 50mm x 75mm x 3600mm of Nigerian grown Iroko hardwood were bought, seasoned naturally and 200 pieces of samples were prepared for determination of their strength properties, (which include bending strength parallel to grain, tensile strength parallel to grain, compressive strength parallel to grain, compressive strength perpendicular to grain and shear strength 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 grown Iroko timber, in accordance with BS 5268 were carried out under the Ultimate Limit State of loading (ULSL). 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 Iroko timber, span of the beam as well as the end bearing length. The result revealed that the Nigerian grown Iroko 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 grown Iroko timber bridge beam in bending, shear, compression and deflection are respectively, under the specified conditions of loading.

Structural performance of the Nigerian grown Abura timber bridge beam subjected to compression and shearing forces

“…However, it is obvious that the Nigerian grown Abura timber is not safe in shear as bridge beam under the stated design conditions. This explains why each timber specie should be subjected to structural reliability analysis because Aguwa and Sadiku (2012) reported that the Nigerian grown Ekki timber in shear is reliable under the same design conditions. The reliability of the Nigerian grown Abura timber in shear can be improved if satisfactory dimensions are chosen by decreasing the span and increasing the depth of the beam.…”

“…The natural seasoning was preferred to artificial seasoning which is faster because the proposed timber structure is bridge, which is always completely exposed to natural weather conditions (Aguwa and Sadiku, 2012) Twenty (20) test specimens were used each for compression and shear respectively. The Universal Testing Machine (UTM) used has a capacity of 50kN and was in good working condition.…”

Reliability-based Evaluation of Bending Moment Magnifiers for the Design of Reinforced Concrete Short Columns under Biaxial Bending

“…This decrease of safety index () of the magnifier for the design of rectangular short column under biaxial bending implies a decrease of the reliability of the column designed using the magnifiers of [15]. This decrease in the reliability index could be attributed to the fact that the carrying capacity of the structural element is being exceeded thereby leading to the chances of failure [31]. A maximum of 5 kN/m 2 live load was adequately sustained by the column at the specified loading and geometric properties.…”

STRENGTH CHARACTERISATION AND CLASSIFICATION OF COMBINED GLULAM BEAM MADE FROM OPEPE (Nauclea diderrichii) AND OBECHE (Triplochiton scleroxylon) TIMBERS

“…These names can be confusing since some softwoods exhibits greater strength properties than some hardwoods and vice versa (Ohagwu & Ugwuishiwu, 2011). Subjecting Nigerian grown timbers to engineering investigations is to establish adequate data and sufficient information for it to be adequately managed and help in building more confidence in identifying their specific areas of usage for structural safety (Aguwa et al, 2015;Mohammed, 2017;Rahmon & Jimoh, 2020). This is expected to lessen the over-dependence on foreign materials for structural applications and to create more employment opportunities that will impact the country's economy (Aguwa et al, 2015).…”

“…Subjecting Nigerian grown timbers to engineering investigations is to establish adequate data and sufficient information for it to be adequately managed and help in building more confidence in identifying their specific areas of usage for structural safety (Aguwa et al, 2015;Mohammed, 2017;Rahmon & Jimoh, 2020). This is expected to lessen the over-dependence on foreign materials for structural applications and to create more employment opportunities that will impact the country's economy (Aguwa et al, 2015). The development of local contents has to be encouraged towards infrastructural developments in developing countries like Nigeria using sustainable and environmentallyresponsive approach (Bakar et al, 2004;Aguwa & Sadiku, 2011).…”