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

Abstract

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 509.80 and 849.67 kg/m3 respectively. 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 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 respectively for 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.