The effect of stem and root-plate defects on the tree response during static loading – numerical analysis

Abstract Despite continual development of the tree pulling test, there is no systematic study on the interaction of stem and root-plate stiffness in relation to tree assessment results. New methods involving numerical modelling and optical techniques provide tools for effective and deeper understanding of the interaction of stem and root-plate stiffness. Within this study, a finite element (FE) model of the tree response to static loading was developed, and the interaction between the stem and root-plate stiffness was analysed on three levels: longitudinal stem strains, root-plate inclinations and stem deflection curve. The model was validated at all three levels by comparison with experiment. Sensitivity analysis of the validated model showed a significant correlation of root-plate stiffness represented by the root volume and soil elastic modulus to the tree response. By analysing the defects in tree response, the importance of proper location for detection of strains and inclinations was demonstrated, especially regarding asymmetrical defects. A numerical estimate of the second derivative of displacement based on the Taylor approximation, was used to analyse the stem deflection curve.