| dc.description.abstract | The timber industry plays a significant role in the economy of Uganda as it contributes to both the domestic and international trade. However, there is lack of sufficient data of a certain species of timber to ensure that the relevant performance criteria are met as specified in the relevant standards and codes. This poses the biggest challenge of using timber as a structural element. This project was aimed at characterization and grading of six timber species on the Ugandan Market out of the thirty-one which were not graded by (Zziwa et al., 2010).
The main objective of this research was investigating physical and mechanical properties of timber species on the Ugandan market and grading them according to EN 338 (2009).The six timber species were Canarium schweinfurthii (Muwafu), Ficus ovata (Mukokoowe), Antiaris toxicaria (Kirundu), Cupressus lustanica (Cypress), Mitragyna stipulosa (Nzingu) and Entandrophregma cylindricum (Muyovu).
To attain this research objective, we collected timber boards from timber yards and they were seasoned using a kiln drier. After seasoning, the boards were reduced to different specimen sizes and the laboratory works proceeded . Laboratory tests involved a range of physical and mechanical properties such as moisture content, density, compression parallel to the grain, Modulus of Rapture and Modulus of Elasticity.
The density was conducted according to EN 408(1995) and 45 samples were used for each specie. The compression parallel to grain was conducted according to BS 373 (1957) where 40 specimens of 20mm by 20mm by 60mm were used for each specie and tested using a UTM. The MOR and MOE tests were carried out according to BS 373(1957) where 40 samples of 20mm by 20mm by 300mm were also tested using a UTM at a loading rate of 6.6mm per sec.
The collected data was analyzed using statistical techniques using excel and the other mechanical properties were derived using equations stated in EN 384:2004. After attaining the physical and mechanical properties, the six timber species were graded according to EN 338(2009) on attainment of the lead properties being characteristic bending strength, mean modulus of elasticity and characteristic density in accordance to EN 14081-3:2005 (E).
Each species was then assigned a strength group from the strength groups (SG4, SG8, SG12, SG16) developed by Zziwa et al., 2010 on achievement of the allowable bending strength. This grading system was entirely designed to take care of the strength characteristics only. Classes SG8 and SG12 are recommended for building construction where stiffness is a controlling factor and where the strength characteristics are not critical. Kirundu, Muyovu and Muwafu belonged to SG12, Mukokoowe belonged to SG8, Cypress belonged to SG4 and Nzingu belonged to SG16. | en_US |
