• Schickhofer, Gerhard
• Freytag, Bernhard
• Brandner, Reinhard

Abstract

According to EN 408, the shear modulus can be determined by means of two standardized test<br/>methods, i.e. the single span method and the variable span method. In the last few years, two<br/>further methods, namely torsion tests and ‘shear field’ tests, have been developed and are now also<br/>performed in testing practice. The latter is based on a relatively simple and reproducible<br/>measurement of the shear distortion by means of standardized four-point bending tests according to<br/>EN 408. The measuring instruments are applied within the areas of constant transverse force. They<br/>are arranged symmetrically with respect to the neutral axis, which results in four ‘shear fields’<br/>under investigation (left-right, front-back).<br/>The practical results, gained from performing standardized test methods, torsion tests as well as the<br/>measurement of shear distortion within ‘shear fields’ on glued laminated timber beams (GLT) of<br/>strength classes GL24h (wg / d g = 150 / 320 mm), as already published by Brandner et al. (2007),<br/>are outlined, discussed and completed by current tests on GL36h and GL36c (wg / d g = 160 / 600<br/>mm). Furthermore, the relation of the shear modulus and the GLT-strength class, in comparison<br/>with solid timber, is treated.<br/>Torsion tests are simple, robust and do not require expensive equipment, but they only provide the<br/>shear modulus G090,tor. This method is proposed for the determination of G-values on specimens of<br/>small cross sections and for obtaining G-values for solid timber. With the measurement of shear<br/>distortion by the application of ‘shear fields’ on specimens tested in four-point bending according<br/>to EN 408 not only the standard values E m,l , E m,g and fm can be determined, but it allows also an<br/>easy, affordable and robust determination of the material characteristic G-modulus. The ‘shear<br/>field’ test method is proposed and approved for GLT with dg ≥ 300 mm. A proposal for the<br/>consideration of both methods within the testing standard EN 408 is presented.

Topics

• impedance spectroscopy
• strength
• bending flexural test
• torsion test