PREDICTION OF THE DYNAMIC PROPERTIES OF A CROSS LAMINATED TIMBER PLATE FROM AN INVESTIGATION OF THE EIGENMODES USING A SCANNING LASER VIBROMETER

摘要

Cross Laminated Timber (CLT) panels of multiple layers are used in Swiss building constructions. There are a variety of dynamic and static methods to determine the elastic constants of a plate e.g. time of flight measurements to determine longitudinal wavespeed [1], determining the elastic constants by optimisation of a Finite Element Method (FEM), direct measurement (in situ) of the bending wavespeed [2], and static measurement using a four point bending stiffness method [3]. Previous studies have shown that for cross laminated timber, determining the stiffness of whole panels is preferable to strip samples because the bending stiffness of CLT varies within a single panel, particularly panels with large lamellas, local non-homogeneities and defects, and the panel stiffness can also depend on the strength grading method of the raw material. Therefore strip sample testing requires a number of narrow strips (e.g. 5 or 6 100mm strips) or wider (e.g. 300mm) strips [3]. The advantage of the first three methods described above is that they can be performed on a complete CLT plate. The direct measurement of bending wavespeed can also be done in situ. In previous work [1] the first two methods were compared, and it was shown that time of flight measurements are not suited to multilayer anisotropic panels. This paper takes a closer look at the second and third methods; that is the determining the elastic constants by optimisation of a FEM and direct measurement of the bending wavespeed. A dynamic assessment of strip samples of a nominally identical panel is described in [4]. The aim is to estimate the elastic constants of CLT plates in order to provide more detailed input data to predict the sound insulation.