Reliability Assessment of a Solid and Nail-jointed Box-Section African Birch (Anogeissus leiocarpus) Timber Column

Abstract

In an attempt to study the performance of a box-section timber column, a structural reliability analysis was carried out on the Nigerian-grown African birch to ascertain its usability for columns under several axial loads. Samples of the timber were bought, sawn and used to prepare small clear specimens of box columns after which their compressive strengths were obtained. Results of corresponding solid square sections of the same timber specie were used as the control. Some statistical parameters 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). From the reliability analysis, both sections were found adequate to support the design load however, it was found out that only beyond 100kN is there an advantage of the box-section above the solid. The compressive capacity of the box-section (150 x 150mm) was found to be 1.5 times that of the solid section and this margin increases to more than two times the solid section as the design load was increased to 1000kN. Also, the box section has a higher capacity to bear its Euler load with a greater length than the solid section because of its greater radius of gyration and rigidity. Therefore the box section would rather be preferable for long columns than the solid section. Lastly, the box-section is also economically advantageous considering the area of the design section- 10,400mm² over the solid section offering a cross sectional area of 22,500mm².