The shear modulus of timber and timber-based composite materials is a fundamental mechanical property, which is used in the design of timber and engineered wood products. The problem of experimentally determining appropriate values of shear modulus for timber-based composite is not as simple and straightforward as in isotropic materials. Although the torsion test is a recommended standard approach to determine the shear modulus of structural-size timber and glulam beams, it is difficult to measure the rotational deformations of the timber beams. Therefore, in this paper, a stereo camera system combined with a photogrammetric approach is proposed to evaluate the values and variations of the shear modulus of glulam beams under the torsion test. The photogrammetric approach is a non-contact method, which provides an efficient and alternative approach for measuring the deformations of the torsion specimens in three dimensions. A series of experiments was conducted on glulam timber beams under the torsion test to investigate the applicability of the optical approach to evaluate the values and variations of shear modulus as well as to investigate the effect of applying torques in a clockwise or anticlockwise direction on the shear modulus of the beams. This optical system not only allows the performance and reliability of the traditional sensors to be assessed, but also allows the rotational deformation of the torsion samples to be monitored at various locations. This enables the values of shear modulus at different cross-sections of the torsion specimens to be evaluated without the need to use more devices. The test results showed that applying torques to the glulam timber specimens during loading and unloading in either a clockwise or anticlockwise direction does not influence or cause a significant change in the shear modulus of the beams. By comparing shear modulus values of glulam beams measured based on different shear spans, it was found that the larger the shear span the smaller the shear modulus value. This might indicate that the variations of shear modulus values at these different gauge lengths need to be considered.

木材和木基复合材料的剪切模量是一种基本的力学性能，用于木材和工程木制品的设计。通过实验确定木基复合材料的适当剪切模量值的问题不像各向同性材料那样简单和直接。尽管扭转试验是确定结构尺寸木材和胶合木梁剪切模量的推荐标准方法，但很难测量木梁的旋转变形。因此，在本文中，提出了一种结合摄影测量方法的立体相机系统来评估扭转试验下胶合木梁剪切模量的值和变化。摄影测量方法是一种非接触式方法，这为测量扭转试样的三个维度的变形提供了一种有效的替代方法。在扭转试验下对胶合木梁进行了一系列实验，以研究光学方法在评估剪切模量的值和变化方面的适用性，以及研究顺时针或逆时针方向施加扭矩对剪切的影响梁的模量。该光学系统不仅可以评估传统传感器的性能和可靠性，还可以在不同位置监测扭转样品的旋转变形。这使得在不需要使用更多设备的情况下评估扭转试样不同横截面的剪切模量值。测试结果表明，在加载和卸载过程中以顺时针或逆时针方向对胶合木试样施加扭矩不会影响或导致梁的剪切模量发生显着变化。通过比较基于不同剪切跨度测量的胶合木梁的剪切模量值，发现剪切跨度越大，剪切模量值越小。这可能表明需要考虑这些不同标距长度下剪切模量值的变化。发现剪切跨度越大，剪切模量值越小。这可能表明需要考虑这些不同标距长度下剪切模量值的变化。发现剪切跨度越大，剪切模量值越小。这可能表明需要考虑这些不同标距长度下剪切模量值的变化。