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Flexibility limits bending in wind: trees


A twisted tree on Craigneston Hill / Walter Baxte.. / LicenseCC-by-sa - Attribution Share Alike

The trunks of trees reduce their tendency to bend in the wind due to their torsional flexibility.

"Another use of torsional flexibility, perhaps less sophisticated, happens on a larger scale. Wind on a tree will twist it unless everything (including the wind) is perfectly symmetrical about the trunk. But twisting brings bits of tree closer to a downwind orientation and brings the bits into closer proximity to each other. Both should reduce the tendency of the tree to bend over. Clever--lowering torsional stiffness ought to reduce the requirement for flexural stiffness! While we don't have data for any intact tree, the effect has been shown for clusters of leaves (Vogel 1989), and casual observations in storms suggest that it works on larger scales. Tree-level use is consistent with the relatively low values of torsional stiffness of fresh samples of tree trunks and bamboo culms (Vogel 1995b)." (Vogel 2003:382)
About the inspiring organism

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Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

Bioinspired products and application ideas

Application Ideas: Incorporating materials with torsional flexibility into building designs and structures, particularly in coastal cities prone to wind storms and hurricanes; microstructures on wind turbine blades that allow them to continue functioning in high winds; wind turbine towers that flex with the wind; more aerodynamic cars, semi trailers and cabs, with structures that 'twist' to reduce drag.

Industrial Sector(s) interested in this strategy: Architecture, construction, structural engineering, wind energy, automotive, transportation

Steven Vogel

Biology Department, Duke University
Vogel S. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
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