Numerical analysis of the adhesive effect on moisture-induced stresses and deformations in CLT panels




Afshari, Zahra

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Sustainable materials such as cross-laminated timbers (CLT) are increasingly being used in the construction of green buildings worldwide. Such products may be exposed to cyclic environmental conditions and exhibit moisture-induced damage. The main objective of this study is to develop and validate an efficient, physically-based tool to simulate the moisture transport, and consequently moisture-induced stresses and deformation in laminated orthotopic composites. Predicting the moisture profile variation with time is the first step toward understanding the performance of CLT panels under extreme environmental loads. A comprehensive literature review was conducted to determine the most critical parameters in moisture transport phenomena in CLT panels to ensure the capability of the framework to capture the essential moisture transport mechanisms. Thermal moisture analogy theory was used for simulating the moisture transport across the composite material cross-section. Unlike previous studies, the moisture adsorption curve of the material was used instead of employing the surface emission coefficient to estimate moisture flux at the surfaces. The method was verified and validated based on a simple one-dimensional (1-D) analytical model and experimental data, respectively. A series of parametric studies were conducted using the validated model to highlight the effect of glue lines, wood species, boundary conditions, panel dimension, and orientation of CLT layers on the moisture transport across the composite panel. After predicting the moisture profile of CLT panels, the numerical model was used to determine the stresses caused by humidity differences on panel surfaces. The applied transient load in the model was obtained from the moisture transport simulation. The total strain rate is assumed as the sum of the elastic and the moisture-induced strain rate. The mechano-sorptive strain is omitted from the material model since it is assumed that samples are not under mechanical loading. The stress model was successfully validated by experimental data reported in the literature. Parametric studies were conducted to investigate the significant role of panel bonding lines (i.e. elasticity modulus and moisture diffusivity) on moisture-induced stresses. A failure analysis was completed to determine how wood species affect laminated composite failure. The same approach was followed to determine the moisture-induced deformation through a finite element analysis. Finally, the effect of adhesive elasticity and its moisture diffusivity on the deformed shape of CLT panels was investigated parametrically. This study showed that the choice of adhesive along with the combination of wood species, could significantly affect the panel’s moisture profile and developed stresses even after 14 days under similar environmental conditions. As demonstrated in this thesis, simulating moisture transport in CLT panels is crucial in determining stresses and deformation caused by environmental conditions.



CLT_ Moisture_ FEM