TORSIONAL SHEAR STRENGTH PROPERTIES OF MALAYSIAN TROPICAL TIMBER IN STRUCTURAL SIZE

Abstract

The shear strength of timber joists in timber design is important, especially to provide an adequate torsional stability and to avoid vibrational serviceability problems. In Malaysia, the data of shear strength of timber is available in MS544 Part 2. The data were developed by shear block test with small samples without defect known as small clear samples. Torsion test is one of the other approaches that can be used to attain the state of pure shear as it does produce a purer and a clearer shear stress distribution in the specimen, allowing measurement of the pure shear properties. However, in Malaysia, very little attention has been paid to the use of the torsion test in evaluating shear strength. Therefore, this study aims to investigate the torsional shear strength of selected Malaysian tropical timbers of different strength groupings (SG) namely Balau (SG1), Kempas (SG2), Kelat (SG3), Kapur (SG4), Resak (SG4), Keruing (SG5), Mengkulang (SG5), Light Red Meranti (SG6), and Geronggang (SG 7) using structural size timbers in accordance with BS:EN 408 and then compared with published by MS554: Part 2. The result shows contradictions of strength grouping between findings and published by MS554: Part 2. Resak (SG4) and Mengkulang (SG5) grade stress value have risen towards SG 3. Geronggang is currently in the SG6. Also from the findings, Kelat (SG3), Kapur (SG4) and Keruing (SG5) grade stresses are at par towards each other, even though they are completely in the different strength group as stated in MS544: Part 2. In conclusion, shear strength data need to be re-examined, since the strength for the tested specimen is much higher than the data given in MS 544 Part 2. This will lead to the increment in section and wastage in cost.