Reliability-Based Calibration of Partial Safety Factors for Bending Design Criteria of Nigerian Mahogany ( Khaya ivorensis) Timber, Beams Based on Eurocode
Abstract
Timber is a vital structural material known for its sustainability, strength, and lightweight properties. However, its variability in mechanical properties necessitates the use of reliability- based design approaches for safety calibration. This study focuses on the reliability-based calibration of partial safety factors for the bending design criteria of Nigerian Mahogany (Khaya ivorensis) timber beams in accordance with Eurocode 5. Laboratory experiments, including three- point and four-point bending tests, were conducted to determine the modulus of elasticity (MOE), bending strength, and density of the timber specimens. Statistical analysis using Kolmogorov- Smirnov tests identified lognormal distribution as the best fit for the MOE data, with a mean MOE of 13,000 MPa, a 5th percentile characteristic value of 9,300 MPa, and a standard deviation of 3,600 MPa.. First-order reliability methods (FORM) and genetic algorithms were employed to calibrate material safety factors, showing that these factors varied with the target reliability index. Based on these findings, Nigerian Mahogany was classified as Strength Class D18 under EN 338 (2009), aligning it with international design standards. This study highlights the importance of reliability-based calibration in timber design and supports the need for localized safety factors in Nigerian timber engineering practices (1.36 and 1.7 respectively) Standing for dead load and live load respectively. The results contribute to the development of efficient, safe, and sustainable structural applications for timber in compliance with modern design codes.
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