INVESTIGATION OF CREEP BEHAVIOUR OF BLACK AFARA (Terminalia ivorensis) TIMBER

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Department of Engineering

ABSTRACT
This study, investigated the creep behaviour of Black Afara (Terminalia ivorensis) timber in accordance with EN 408 (2004) and EN 13153 (2002). The data were analysed based on the Eurocode 5 (2004), Eurocode 0 (2002), JCSS (2006) and EN 384 (2004) specifications using Easyfit statistical package. The statistics of the reference material properties (density, bending strength and modulus of elasticity) were calculated. The mean value of the density was found to be 449.24kg/m3. The corresponding coefficient of variation is 15%.The mean values of the modulus of elasticity is 16171N/mm2, and the corresponding coefficient of variation is 21%. For the bending strength, the mean value was given by 81.05N/mm2. The corresponding coefficients of variation is 16%. The mean values were adjusted to 12% and 18% moisture content, to agree with the European and Nigerian reference moisture contents. Five theoretical distribution models (normal, lognormal and gumbel, weibull and frechet) were fitted to the reference material properties using kolmogorov smirnov statistical distribution fitting technique. The best fit theoretical distribution models were found to be normal distribution for density, Lognormal distribution for modulus of elasticity and Weibull for bending strength. The Terminalia ivorensis timber specie was graded in accordance with the requirements of EN 338 (2009). This yielded the appropriate strength of D18. One-year creep test was measured from the laboratory experiments on Terminalia ivorensis timber samples. The creep data were fitted to linear, exponential and logarithmic regression models. The coefficients of determination for each of the model was determined. The logarithmic model has the highest correlation with coefficient of determination of 0.941. This implied that, logarithmic regression model is the most appropriate to model the creep behaviour of the timber. The selection of the logarithm models was buttressed by the values obtain from regression modelling error analysis. Microstructure analysis was conducted on the Terminalia ivorensis timber specie using scanning electron microscope on the specimen. The analysis was conducted before and after creep deformation. The microstructure analysis revealed that, the cellular structure contained empty vessels which was found to have closed after creep deformation. This implied that, the application of the long term loading lead to the closure of the empty vessels within the cells microstructure, leading to the densification of the timber.