Abstract
The Nigerian-grown African birch timber was used to assemble I- section specimens which were tested in the laboratory for their compressive strengths. Solid square sections of the same specie were similarly tested for an apt comparison of results. A structural reliability analysis was carried out for these two sections to ascertain their performance as structural timber columns using statistical parameters that were determined for the deterministic design of the timber column. A FORTRAN-based program was also developed and used for the reliability analysis of the Nigerian-grown African birch columns designed to ascertain their level of safety using First-Order Reliability Method (FORM). The ‘I’- section was found unsafe to bear the design load unlike its corresponding solid section. An identified I- section of (100 x 400mm) was found adequate (with Pf =1.22 x 10-02) whose compressive resistance corresponds to (200 x 100mm) of the solid section (with Pf =7.76 x 10-02) which is practically half the dimension of the I-section. This shows that the solid section has a capacity twice that of the ‘I’- section of equal dimensions. However, considering the minimum dimension of the of the two sections capable of supporting the design load, the ‘I’- section is more economical than the solid section since it offers a less effective area of 11,200mm2 compared to the solid section with an effective area of 20,000mm2 . The ‘I’-section also showed a higher capacity to bear the Euler load with greater lengths than the solid section because of its greater radius of gyration and rigidity value and would be rather preferable for long columns than the solid section. Considering the limited availability of larger dimensions of solid sections, the built-up I- section would be more relevant where large sized sections are required.Keywords: Solid section, Compressive capacity, Built-up sections, Reliability, Probability of failure (Pf)
Highlights
The Nigerian-grown African birch timber was used to assemble I- section specimens which were tested in the laboratory for their compressive strengths
A solid African birch column was compared to an I-section of corresponding dimension to evaluate the performance as well as their capacity
When putting to consideration the design dimension- (150 x 150mm) for the I and solid section subjected to similar load ranging from 75kN to 350kN, it was observed that the solid section possesses a higher safety index than the ‘I’- section by more than 3.0 and from a load of 200kN and above, the I- section begins to tend to failure
Summary
The Nigerian-grown African birch timber was used to assemble I- section specimens which were tested in the laboratory for their compressive strengths. Wilson et al (2018) in a study on a reliabilitybased design of a solid African birch timber column showed that the Nigerian-grown African birch is a satisfactory structural material for use as solid timber columns at a depth and breadth of 150mm, effective length of 3600mm and an axial load of 260kN; with a probability of failure 8.85 x 10-3. Aguwa and Sadiku (2011) from a reliability studies showed that the Nigerian Ekki (Lophira alata) 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. Aguwa (2012) showed from a reliability studies that the Nigerian grown Apa (Afzelia bipindensis) timber is a satisfactory structural timber for bridge beams at depth of 400mm, breadth of 150mm and span of 5000mm under the Ultimate Limit State of Loading. The probabilities of failure of the Nigerian Apa timber bridge beam in flexure and deflection are 2.062×10−3 2.673×10−14respectively, under the design conditions
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