Inferring Strength Of Structural Timbers From Small Clear Specimen Strength Test Data
Naku Ziraba, Yasin
Mwakali, Jackson A.
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Despite the existence of diverse timber species in least developed countries such as Uganda, wood has been underutilized in the construction sector on grounds of its perceived unreliability due to lack of adequate strength data. Attempts have been made to establish strength of small clear specimens but the relationship between MOE and MOR of small clear specimens and structural size tropical timber is not documented. Therefore this research was conducted to compare the flexural strength of small clear to that of structural size specimens; and particularly the effect of knots on MOE and MOR of structural size timber. Small clear tests were conducted in bending, compression and shear parallel to grain using standard procedures of the American Society for Testing and Materials (ASTM), ISO 8905 (1988), and BS 373 (1957). Structural size bending tests were conducted following ASTM ISO 8905 (1988), AS/NZS 2878 (2000); BS 4978; ASTM D198-02; ISO/FDIS 13910:2004 and BS 373 (1957). It was concluded that structural size MOE and MOR can be estimated from small clear MOE and MOR using reduction factors of 40% and 20% respectively. It was recommended that more research into the effect of complex knots, cross-grain and grain angle on timber strength be done for better structural grading of timber.