地表面粗度の状況が異なる地点における地表面近傍の風の性状

概要

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For the wind resistant design of low-rise buildings and the assessment of pedestrian-level wind environment around buildings, it is important to understand the characteristics of natural winds near the ground surface, e.g. profiles of the mean wind speed and turbulence intensity and the gust factor. In the 'AIJ Recommendations for Loads on Buildings1) (2004)', the profile of mean wind speed is specified as constant up to a height Zb corresponding to the terrain category, beyond which it is expressed by a power function of height Z above the ground. Such a vertical profile of mean wind speed may overestimate the wind loads near the ground surface, significantly. In order to evaluate the design wind loads as well as to assess the wind environment more reasonably, the characteristics of winds near the ground surface should be understood in more detail. The authors have carried out full scale measurements of wind speeds near the ground surface at various sites with different terrains, where the time history of wind speeds at two or three heights up to 10 m was obtained. The present paper discusses the characteristics of winds near the ground surface, i.e. profiles of mean wind speed and turbulence intensity, turbulence scale, gust factor and power spectrum, based on the results of these full-scale measurements.