Modeling of Compressive Strength Characteristics of Structural-sized Afara (Terminalia superba) and Babo (Isoberlinia doka) Timber Columns Using Constant Failure Rate (CFR) Model of Reliability

Document Type : Regular Article


Department of Civil Engineering, Faculty of Engineering and Technology, University of Ilorin, Ilorin, Nigeria


This paper investigated the reliability of the Structural-sized Afara and Babo timber species as column materials. The work centers on the compressive strength characteristics of Nigerian Afara (Terminalia superba) and Babo (Isoberlinia doka) timber column of nominal lengths 200, 400, 600 and 800 mm and a nominal width and thickness of 50 mm by 50 mm. The steps involved collection and conditioning of Afara and Babo timber species, preparation of test specimens, determination of physical properties such as moisture content and density, determination of compressive strengths using varying heights of 200, 400, 600 and 800 mm and derivation of continuous column design equations. Forty test samples were used in all the tests carried out. Afara and Babo have an average density of 509.80and 849.67 kg/m3 respectively. The moisture content of both species less than the maximum recommended value of 20 % and the average strength at yield of Afara and Babo are 19.99 and 30.96 N/mm2. The derived continuous equations for the design of Afara column and Babo column are σ=16.992e0.0039λ and σ=32.031e-0.001λ respectively. The results of the reliability analysis show that Afara and Babo timber species have reliability index of 0.63 and 0.64 respectivelyfor a service life of 50 years, assuming other serviceability conditions are met. This design procedure is distinct and more effective than the usual procedure of classification of compression members as short, intermediate and long.The paper therefore recommends the adoption of these equations for the design of compression members from these timber species in Nigeria.


Google Scholar


Main Subjects

[1]     Aguwa JI, Chukwu PC, Auta SM. Characterization and Grading of South Eastern Nigeria grown Irvingia gabonensis Timber in Accordance with BS 5268. USEP J Res Inf Civ Eng 2015;12:720–31.
[2]     A. A. Jimoh, R. O. Rahmon OYB and OLT. Characterization and Classification of Ayunre (Albizia zygia) Timber Specie grown in Kwara State Nigeria in accordance to bS 5268 nad NCP 2. Epistemics Sci Eng Technol 2017;7:549–57.
[3]     Apu SS. Wood Structure and Construction Method for Low-cost Housing. Int. Semin. Build. Mater. Low-cost Housing, Indones., 2003, p. 7–28.
[4]     material RF-W handbook: wood as an engineering, 2010  undefined. Wood as a sustainable building material. FsUsdaGov n.d.
[5]     Karlsen G, Slitskouhov Y. Wooden and plastic structures, Mir Publishers Moscow, 1st Edition USSR. 1989.
[6]     Aguwa JI. Reliability studies on the nigerian timber as an orthotropic, elastic structural material. 2010.
[7]     Robert JM. Buckling of Bars, Plates and Shells. 2006.
[8]     Aguwa JI. Structural Reliability Analysis of the Nigerian Ekki Timber Bridge Beam Subjected to Deflection under the Ultimate Limit State of Loading, presented and published in the Book of Proceedings. 2nd Bienn. Eng. Conf. Titled Energy, Glob. Environ. Chang. Food Secur. Eng. Infrastructure, Organ. by Sch. Eng. Eng. Technol. Fed. Univ. Technol. Minna, Niger., 2011, p. 311–8.
[9]     Ajamu SO. Optimal design of cement-lime plastered straw bale masonry under vertical load and thermal insulation for a residential building, Ph. D Thesis report submitted to the department of Civil engineering, faculty of Engineering and Technology, University of Il. Ph. D Thesis report submitted to the department of Civil engineering, faculty of Engineering and Technology, University of Ilorin, 2014.
[10]    Ghasemi SH, Nowak AS. Target reliability for bridges with consideration of ultimate limit state. Eng Struct 2017;152:226–37. doi:10.1016/j.engstruct.2017.09.012.
[11]    R. D. Leitch. Basic Reliability Engineering Analysis. 1st Edition. 1988.
[12]    Nowak AS. Survey of textbooks on reliability and structure. 2004.
[13]    Ghasemi SH, Nowak AS. Reliability index for non-normal distributions of limit state functions. Struct Eng Mech 2017;62:365–72.
[14]    Thelandersson S, Larsen HJ. Timber engineering. John Wiley & Sons; 2003.
[15]    Aguwa JI, Sadiku S. Reliability studies on the Nigerian Ekki timber as bridge beam in bending under the ultimate limit state of loading. J Civ Eng Constr Technol 2011;2:253–9. doi:10.5897/JCECT11.052.
[16]    EN BS. 408, Timber Structures–Structural Timber and Glue-laminated Timber–Determination of some Physical and Mechanical Properties. 2003.
[17]    Standard B. BS 373: Methods of Testing Small Clear Specimens of Timber. Br Stand Institution, London 1957.
[18]    Jimoh AA, Rahmon RO, Joseph SG. Evaluation of compressive strength characteristics of structural-sized Apa (Afzelia bipindensis) and Opon (Lannea schimperi) timber species columns found in Nigeria. J Appl Sci Environ Manag 2018;21:1281. doi:10.4314/jasem.v21i7.10.
[19]    Osuji SO, Nwankwo E. Investigation into the Physical and Mechanical Properties of Structural Wood Commonly Used in Nigeria: A Case Study of Benin City. J Civ Eng Res 2017;7:131–6. doi:10.5923/j.jce.20170705.01.
[20]    W. P. K. Findlay. Timber Properties and Uses. Forest Product Research Laboratory, Granada Publishing by Crosby Lockwood Staples, London, Toronto, Sydney, New-York, United State of America. 1975.
[21]    Nabade AM. Development of Strength Classes for Itako (Strombosia pustulata), Oporoporo (Macrocarpa bequaertii), Opepe (Nauclea diderrichii) and Ijebu (Entandrophragma cyclindricum) Nigerian Timber species based on EN 338 (2009). 2012.
[22]    Jimoh AA, Aina ST. Characterisation and grading of two selected timber species grown in Kwara State Nigeria. Niger J Technol 2017;36:1002–9.
[23]    Ibitolu BJ, Jimoh AA. Characterization and Grading of some Potential Nigerian Timber Species in accordance to Eurocode EN 338 (2009). 2nd Int. Eng. Conf. (IEC 2017). Fed. Univ. Technol. Minna, Niger., 2017, p. 433–40.
[24]    Adedeji A. Reliability-Based Probability Analysis for Predicting Failure of Earth Brick Wall in Compression. Niger J Constr Technol Manag 2008;9:25–34.
[25]    Abdulraheem KK. Reliability Index Assessment of Solid and laminated teak Wooden Deep I-Beam for residential Building. M. Eng. Thesis report submitted to the Department of Civil Engineering, Faculty of Engineering and Technology, University of Ilorin, Nigeria. Thesis report submitted to the Department of Civil Engineering, Faculty of Engineering and Technology, University of Ilorin, Nigeria, 2016.
[26]    A. A. Jimoh. A continuous column design formula at ultimate strength for axially loaded Iroko (milicia excelsa) timber column. Niger J Pure Appl Sci Fac Sci Univ Ilorin, Niger 2007;22:2129–35.