Cross-laminated timber (CLT) is a panel-shaped engineered wood product, assembled of layers of lamellas (mostly softwood) with perpendicular orientation of the grain direction. In contrast to other panel-shaped engineered wood products, CLT is not used as components of structural elements, but rather as load bearing plates and shear panels. The design of CLT used as load-bearing plates is often governed by serviceability criterions like maximal deflection and vibration susceptibility. Hence, predicting the respective behaviour of such panels requires accurate information about their elastic properties. With the aim of determining the global elastic properties of full-scale CLT panels directly in the production line, a fully automatic, non-destructive procedure based on experimental and theoretical modal analysis was developed: Resonance frequencies and mode-shapes of the plates are determined first by means of an experimental modal analysis. A simulation model based on Reddy's higher order plate theory is then used to analytically calculate natural frequencies and mode shapes as functions of the unknown elastic parameters. Finally, in an optimization process two in plane moduli of elasticity and three shear moduli can be identified by minimizing the differences between measured and analytically estimated resonance frequencies. First, the method was investigated in the laboratory. The applicability of the method was then proven on 42 CLT panels with different dimensions, layer sizes and from different producers, and validated by static bending experiments on full-scale panels and panel-bars. Finally the procedure was optimized for the application in the production line.
