Assessing the Risk of Failure of a Remarkable Old Tree on Dwelling Place due to Storm Winds

Remarkable old trees are part of human’s lives and interact directly and daily with them, influencing space and neighborhood with their positive and elegant colors, brightness and odors. In summer time, families can advantageously have picnic nearby their refreshing atmosphere, spend time reading a book under their leaf and children use to play football protected by their branches from the sun being a little too strong. As human (Perhaps more than them), they nowadays health problems, heavy thermal, environmental and mechanical stresses. Even if they are leaf woods or conifers, they are smart! They learn from their environment! Their mechanical properties, geometrical inertia and stiffness vary with their texture, water content and elderly. But what about their resistance to nowadays sudden actions coming from global warming? Will such remarkable giants resist strong winds, heavy rain or brutal storms increasing shortly here and there? How to assess the risk of failure and to avoid potential injuries to the public due to (heavy) branch breaks or trunk outrooting. Understanding their strength sensitivity helps to assess their risk of failure under different extraordinary load case situations. A model of their shape, the collection of their nominal mechanical properties, the appreciation of the variability of those properties (Degraded properties) and the assessment of given boundary conditions in order to assess the reserve of strength and to discuss the risk. In a first part, the current article reviews the wood characteristics, their variability and the factors affecting them mechanical behavior. The second part treats the case of a remarkable fir > 70 years old remarkable of more than 25 m height, planted in the middle of a residential area and intends to show how that analysis was performed, the number of hypothesis done and their vraisemblance but also that such an assessment remains extremely complex.