DEVELOPMENT OF A CORRELATION MODEL FOR TORSIONAL SHEAR MODULUS PROPERTIES BETWEEN STRUCTURAL SIZE SPECIMENS BASED ON EN 384:2016 AND SMALL CLEAR SPECIMENS (MS544: PART 2)

Abstract

In timber design, the shear modulus of beams is crucial for ensuring torsional stability and minimizing vibrational issues. Traditionally, the ratio of modulus of elasticity (E) to shear modulus (G) is assumed to be 16:1. However, bending tests often combine flexural and shear stresses, making it difficult to assess pure shear properties. The British Standard BS EN 408:2012 now recommends the torsion test as the preferred method for determining the shear modulus of structural-size timber and timber composites. This method has received limited attention in Malaysia. This study investigates the torsional shear modulus of Malaysian tropical timber species across different strength groups (SG), including Balau (SG1), Kempas (SG2), Kelat (SG3), Kapur (SG4), Resak (SG4), Keruing (SG5), Mengkulang (SG5), Light Red Meranti (SG6), and Geronggang (SG7). Torsion tests were conducted in line with BS EN 408, and the results were compared with modulus of elasticity values from MS554: Part 2. The findings showed that the E to G ratio for these species ranged from 17:1 to 29:1, with an average of 21:1—exceeding the conventional 16:1 ratio. This indicates that torsional shear modulus must be experimentally tested rather than inferred from the traditional ratio.