Nonlinear numerical approach to the analysis of Cross-Laminated Timber

This research project investigates the shear behaviour of Cross-Laminated Timber (CLT) panels through in-plane shear tests. More precisely, it aims to study the post-elastic behaviour and the damage evolution. Load-displacement curves were experimentally determined, and the Cohesive Zone Model (CZM) is then used to reproduce the experimental results and to identify cohesive crack properties of CLT. A finite element model is used for the identification; it is based on the modulus of elasticity and fibres orientation of Spruce timber. The CZM can capture the nonlinear behaviours and the damage evolution under increasing load, which often occurs in the fracture process zone ahead of the crack tip. In the model, the timber is idealised as an orthotropic elastic quasi-brittle material. These parts are joined by interfaces, simulating the adhesive layers, that have a traction-separation law with a CZM behaviour. The nonlinearity and the fracture behaviour (and the discontinuity, indeed) develop along these interfaces. Before cracking, the “composite” material obeys the rules of orthotropic elasticity. By the comparison of the numerical and experimental stress-strain curves, the main parameters of the CZM are identified. The model shows great potential to predicting the load-carrying capacity of the CLT panels; cohesive elements can be effectively used to investigate the interaction with timber layers where crack propagation can govern the failure of the panel. The results of this work permit to have an accurate model to predict, even in different situations, the nonlinear behaviour of CLT panels, including their fracture behaviour, which could be very important in view of seismic applications in new and existing buildings. Further analysis would help build a complete understanding of the limits and nonlinear properties of this construction material. In first should be enhanced the approach about the initial stiffness of the wooden element due to the possible effects of the adhesive absorption. Additionally, different 3D models should be used for the modelling of the CLT failure with the aim to assess the possibility to obtain a better fitting of the experimental data.