High-voltage transmission lines with an overall length of several hundreds kilometers have been constructed across the mountainous area or the coastal zone, and directional strength characteristics of the transmission tower are found remarkably due to a high rate of wind load. Transmission towers are considered to be designed with enough wind-resistance performance, however, it is necessary to re-examine the current estimation methods from both points of design wind speed and wind load to rationalize the tower design and to improve the structural integrity. In this paper, considering the rationalization of design wind speed, we analysed statistically wind speed data at about 140 meteorological observatories in Japan, resulting 150-year return period wind speed every 8 directions, and simultaneously excuted air flow simulations of the Japanese Islands divided into 4 parts. Using these results, we show a new attempt of basic wind maps showing the 150-year return period of annual maximum 10 minutes-mean wind speed by direction at 10 m above class II roughness terrain.

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Drag of a 6:1 axial-symmetric ellipsoid model parallel to tunnel flow was measured with the NAL 60cm MSBS(Magnetic Suspension and Balance System). The obtained values ranged from 0.045 to 0.055 at Reynolds number of 1 million with reference length of the model. They were compared with data sets of another source measured with a MSBS. The comparison shows that the obtained drag coefficients lie between those of 5 and 8 fineness ratio ellipsoids at Reynolds numbers more than 0.8 million. The drag was also estimated through the wake survey without the support interference. The values of the drag were near to the obtained ones with the MSBS. The observed wake looks like circle in its contour lines because of the support interference free. The flow separation was observed at about 96% chord position from nose of the model by the oil paint visualization.

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