The in situ observations (trees damaged and lump stopped) show that the forest may ensure a significant role of protection against rockfalls. The purpose of our work is to model the mechanical behaviour of a tree subjected to a rock impact using a multiscale approach. First, the time-dependent distribution of pressure, as well as the penetration, the lump speed and the tree damage are determined by modelling the impact on a local scale. This analysis uses temporal discretisation in the balance of linear momentum. Second, the dynamic behaviour of a non-constant section beam is analysed. This beam is loaded by a given time-dependent distribution of pressure. This large-scale model uses the Finite Element Method and Hamilton's principle. Tree roots and branches are taken into consideration. This model provides both an improved kinematic analysis of the lump and an assessment of the protective function of forest stands. The forest's role of protection could thus be enhanced and the design of other protection measures could be optimized.
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