Thursday, February 25, 2016

Critical Wind Speed

Critical wind speed (~94 mph) for tree breakage
Data from storms suggest that the critical wind speed at which trees break is constant (≃42m/s), regardless of tree characteristics.
The research is summarized in this focus article.

Essentially, the authors performed experiments, and observed that wood breaks at a critical curvature radius, which depends on the diameter D and length L of the rod. Generally the relation between the diameter and length of a tree follows a \(D \sim L^{1.5}\) relation. Using a relatively simple mechanical model, and experimental data, and this relation between D and L, they found that the critical wind velocity increases very weakly with length, \(V \sim L^{1/8}\).
The speed does not depend on the elastic modulus of the wood, which is consistent with data showing that hardwoods (e.g., oaks) are just as wind susceptible as softwoods (e.g., pines).

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