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Fujimoto H.,Wind Engineering Institute Co. | Sarukawa A.,Wind Engineering Institute Co. | Miyashita K.,Wind Engineering Institute Co. | Nakamura O.,Wind Engineering Institute Co. | Uematsu Y.,Tohoku University
Journal of Wind Engineering | Year: 2015

The accurate assessment of pedestrian-level wind environment is one of the major issues in the development of urban areas, which is usually evaluated on the basis of wind tunnel experiments. The accuracy of the assessment is directly related to that of wind speed ratio obtained from the wind tunnel experiments. There are some factors producing a difference between the predicted values from the wind tunnel experiments and actual values from field measurements. The present paper focuses on the following two factors. One is the effect of deciduous trees that are not reproduced in the wind tunnel models in most cases. However, there are many deciduous trees in urban areas, which may reduce the wind speeds near the ground significantly. The other is the effect of the wind direction fluctuation at the reference point. The range of fluctuation is generally much smaller in the wind tunnel flow than in the natural winds. The effects of deciduous trees and wind direction fluctuation on the wind speed ratio are investigated based on the results of wind tunnel experiments and field measurements at various locations in Tokyo. Source


Yoshie R.,Tokyo Polytechnic University | Tominaga Y.,Niigata Institute of Technology | Ito S.,Konoike Construction Co. | Okada H.,Izumi Sohken Engineering Co. | And 9 more authors.
Journal of Wind Engineering | Year: 2014

A criterion for pedestrian wind environment based on probability of exceedance of daily maximum gust wind speed is commonly used in Japan. We usually use gust factors to estimate the daily maximum gust wind speeds, using daily maximum mean wind speeds. But there still remains an unsettled problem of how to determine the appropriate gust factors. "A Working Group for Urban Wind Environment Assessment" in the Japan Association for Wind Engineering has been studying this problem to establish rational wind environment assessment method. The WG proposes a model equation of the gust factors based on field observation data at 152 sites, and confirms the applicability of it to the assessment of pedestrian wind environment. Source


Masuyama Y.,Wind Engineering Institute Co. | Nakamura O.,Wind Engineering Institute Co. | Uematsu Y.,Tohoku University | Okuda Y.,Japan National Institute for Land and Infrastructure Management
Journal of Wind Engineering | Year: 2016

Recently, rooftop signboards are often damaged and blown off by strong winds. Flying debris resulting from the damage to signboards may cause second damage to other buildings and people. To prevent such damage, an appropriate wind-resistant design should be done to the signboards. In practice, however, wind force coefficients for rooftop signboards are not provided in the codes and standards in Japan. The present paper investigates the characteristics of wind forces acting on the signboards installed on the rooftop of low-rise and middle-rise buildings on the basis of a wind tunnel experiment, in which the shape, size and location of the signboard are varied over a wide range. Special attention is paid to the time-space correlation of net wind forces acting on the signboard. Based on the distribution of peak wind force coefficients, the signboard is divided into several zones, for which the wind force coefficients are specified. The proposed wind force coefficients shall be used for designing the cladding and components of signboards. Source


Sasaki R.,Wind Engineering Institute Co. | Ohtake K.,Takenaka Research and Development Institute | Goto S.,Obayashi Corporation | Matsui M.,Tokyo Polytechnic University | And 2 more authors.
AIJ Journal of Technology and Design | Year: 2015

For the wind-resistant design of buildings, it is important to understand the fluctuation component of wind. In the AIJ Recommendation for Loads in Buildings (2004), the profile of turbulence intensity and turbulence scale are specified as constant up to a height Zb, beyond which they are expressed by a power function of height Z . In the present study, the relationship between turbulence intensity or turbulence scale and observation height are discussed again, including new observation data. The scatter of observation data is also investigated. Source


Miyashita K.,Wind Engineering Institute Co. | Akahoshi A.,Tohoku University | Sasaki R.,Wind Engineering Institute Co. | Nakamura O.,Wind Engineering Institute Co. | Uematsu Y.,Tohoku University
Journal of Wind Engineering | Year: 2013

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. Source

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