Title: Wind Load Assessment for Ornamental Trees – Past Methods and Current Developments

Summary: Methods to analyse wind actions on structures are an essential part of building codes all over the world. Since 25 years, the proponents of tree-statics have established a system to incorporate engineering principles into hazard tree assessment. One basic element of those static integrated methods is an analysis of wind actions on trees if their stability is in question. The currently used wind load analysis was developed at the University of Stuttgart in the mid eighties by a team of researchers around L. Wessolly and G. Sinn. It was based on the German engineering standards of that time for wind actions on structures. Up to now, roughly 10,000 trees have been successfully tested for structural integrity by means of this protocol. In the meantime, a growing interest in wind actions on ornamental trees lead to further research projects in several countries. The dynamic reactions of trees under wind loading, their frequency response to gusts and the aerodynamic resistance of tree crowns were investigated. At the same time, models for wind exposure and gust reaction in forest canopies were developed. An overview of the results of theses studies will be presented with regard to their applicability to an engineering based wind load assessment for trees in an urban setting. In 2004, European building codes were unified and adapted to currently available wind data. As a result, national standards for assessing wind actions on structures were updated. They provided data on gust speeds in regional wind zones and a new model for dynamic reactions of oscillating structures. These also served for developing new tools to analyse wind action on trees. The technical background of those protocols will be described. Case studies will be used to illustrate how the results of current research on tree dynamics were incorporated and may help to improve the reliability and acceptance of statics integrated methods in arboriculture.

Andreas Detter, Dipl.-Ing. TU, öbuv Baumsachverständige, Gauting, Germany

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