Estimates of gust wind speeds in Kyushu area for a wind hazard map

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(1) The properties of the gust factors of mean wind speed of over 15 m/s were investigated based on the data of the network of wind measurement in Kyushu (NeWMeK) from 1994 to 2002, which has 122 measurement stations, and the digital information of each terrain. The data of each station are arranged by typhoon or non-typhoon, 16 directions of wind, its weather condition and its topography of terrain.(2) It is indicated that the gust factors in typhoon are higher than those in non-typhoon: 1.9 in typhoon and 1.7 in non-typhoon. When typhoon approaches, the gust factor does not decrease even though the mean wind speeds are high. And so a maximum gust speed is estimated to be a much higher wind speed. Moreover, the maximum gust is much higher in southern wind than in northern wind.(3) The property of increase of wind speed at Shiranui-cho of Kumamoto prefecture was investigated by wind tunnel test. It is found that the temperature gradient of the approaching wind profile affects strongly the increase of wind in the lower layer. The stability of a stratified wind flow is enhanced by a cooled plate using a dry-ice box located at the wind tunnel surface. However, it is difficult to estimate the local wind speed in a mixed area such as a deep river and a deep valley floor.(4) Most of the investigation of the relationship between residential damage rates and wind speeds based on information of damaged residential houses by Typhoon Bart(1999) indicate clearer relation to a instantaneous wind speed. For wind speeds of exceeding 30 m/s, the damage rate exponentially increases. In addition, the duration of wind affects strongly the damage rates in case of wind speeds of over 35 m/s.(5) We have produced the instantaneous maximum wind speed map of Kyushu, by combining our information of gust factors and the map of expected wind speeds for a return period of a hundred years. This wind speed map is applicable to suggest a wind hazard map of residential houses and buildings.