There is the need to subject some Nigerian timber species to reliability analysis in order to establish their structural usefulness. It is on this basis that the Nigerian grown Abura timber was studied and structurally assessed to understand its performance as timber bridge beams. This was achieved by preparing some test specimens of it from naturally seasoned samples at moisture content of 18%.and determining its strength properties, which were subjected to statistical analysis to obtain the mean, standard deviation as well as the coefficient of variation. Structural analysis, deterministic design and structural reliability analysis were performed on the Abura timber bridge beam at the Ultimate Limit State of loading. A computer programme developed in FORTRAN language and First-Order Reliability Method (FORM) were used in the reliability analysis. In order to study the effect of geometry and loading on the reliability index, sensitivity analysis was performed by altering the geometrical dimensions of the beam as well as the magnitude of the loadings on the beam. Satisfactory level of reliability indices were recorded at depth of 400 mm, breadth of 150 mm and span of 5000 mm under the ultimate limit state of loading. The Abura bridge beam depicted very low level of safety when subjected to only shearing forces under the specified design conditions. The probabilities of failure of the Abura bridge beam in compression and shear are 0.68 × 10 −5 and 0.023 respectively, under the specified design conditions.

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.

Locust beam pod solution (LBPS) was prepared by extraction from the outer leathery cover of the pod soaked in water for twenty four hours in ten different concentrations of known weight of dried locust bean pod cover in 20 litres of clean water. Using ten levels of these concentrations, five sandcrete blocks of size 150mm cube were produced for each concentration, making a total of fifty blocks and the compressive strengths at 28 days were determined. Using a concentration of 50g/l, twenty blocks were produced with 0, 5, 10, 15, 20, 25, 30, 35 and 40% respectively by weight of cement reduced making a total of 180 blocks. They were subjected to compressive strength test on 7, 14, 21 and 28 days respectively, crushing five blocks in each day to determine their average compressive strength. In order to investigate the effect of duration of soaking the locust bean pod cover in water on the compressive strength of the sandcrete blocks, five blocks were produced using the same concentration of 50g/l but soaked in water for 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 days respectively and their compressive strengths were determined at 28 days. It was found that the higher the concentration of the LBPS, the more the compressive strength and soaking the locust bean pod cover for more than 24 hours is not necessary as the compressive strength tends to decrease. In conclusion, up to 25% by weight of cement can be saved by using locust bean pod solution in moulding the sandcrete blocks.

Compressive strength test was carried out on the protein-based lightweight foamed concrete produced with cement partially replaced by rice husk ash to ascertain its strength characteristics. Standard concrete cubes of 150 x 150 x 150 mm were produced using ordinary Portland cement (OPC), fine aggregate, aqueous protein-based foaming agent and rice husk ash (RHA). The RHA was used to replace cement at 5 %, 10 %, 15 %, 20 %, 25 %, 30 %, 35%, 40 %, 45 % and 50 % by weight of cement. Control cubes with no cement replacement (0 %), were also produced and used as reference points for comparing the compressive strength of the lightweight foamed concrete at 28 days and 56 days respectively. The mix proportion of 1:1.5 was used as binder/fine aggregate proportions with the foam occupying 20 % of the volume of the concrete and the other constituents occupying the remaining 80 %. The compressive strengths of the lightweight foamed concrete at both 28 days and 56 days, increased for cement replacement levels of 5-30 % and gradually decreased for cement replacement levels of 35-50 % respectively for the mix proportion of 1:1.5 and for the water/binder ratio of 0.4. The minimum 28 days compressive strength for the mix proportion of 1:1.5 at cement replacement level of 30 % and water/binder ratio of 0.4 was 15.52 N/mm 2 while that at 56 days was 18.51 N/mm 2. The rice husk ash is a pozzolanic material with a capability of contributing up to 80 % and above to the compressive strength of lightweight foamed concrete, if the percentage replacement does not exceed 30 %. The mix proportion of 1:1.5 at water/binder ratio of 0.4 produces a structural lightweight concrete at 28 days.

This paper presents the results of structural reliability analysis of a structural element (beam) in building using First-order reliability method (FORM) to ascertain the level of safety. The natural stone (NS) which is the by-product of Precambrian deposits of the Bida trough was used as coarse aggregate: unwashed and washed aggregates were used. A total of 80 concrete cubes of 150 mm × 150 mm × 150 mm were cast and used for this study, sensitivity analysis was conducted by varying the span, depth, effective depth, area of shear reinforcement and dead load of the beam in bending. The result of the sensitivity analysis revealed that the beam utilising unwashed and washed NS are both structurally safe at a span of 3000 mm with probabilities of failure of 9.20 × 10–5 and 2.06 × 10–8 and both safe at a depth of 600 mm with probabilities of failure of 4.19 × 10–4 and 2.602 × 10–4, respectively, in bending.