BASIC WIND LOADS AND THE COEFFICIENT OF WIND-LOAD FOR CHINA

The authors are aware of the fact that the various formulas for the determination of basic wind loads have appeared in the engineering literature and also that several forms of wind speed have been recorded at the weather station. Consequently, there exist wide differences in opinion amongst scientists in regard to the question of basic wind load determination; and thereby a study has been undertaken for the express purpose of finding out the basic wind loads as well as an optimum the wind-load coefficient suitable for China.The wind speed from which wind load was obtained has often been defined to mean the highest speed ever recorded at a particular station. As a matter of fact, the recorded data of wind speeds, which have to be based on the climatic conditions, are also subject to the following factors:1. Time-interval over which the mean wind speed is measured,2. The method of observation, i. e. whether the registration is done intermittently or continuously.3. The elevation of anemometer located.Moreover, the extreme values of wind speeds must also rely on the length of recording time which invariably varies from station to station.After having analysed each of the above factors in great detail, the authors strongly propose that for the determination of basic wind load, the mean 10minute wind speed, under the condition of a continuous observation and at a given elevation, shall be adopted. But the extreme value must farther be de rived from a statistical curve over which the annual extreme values of wind speed with certain recurrence interval are given.An effort for selecting a suitable formula for converting wind speed from different elevations to the desirable datum has been done. It has come to their notice that the difference due to the length of time-interval and the method of observation have both influenced greatly the value of recorded wind speeds. ??A series of formulas has been developed for the convenience of necessary conversion of all available data into the corresponding figures for the calculation of extreme values. On account of limited data available, the authors do not attempt to arrive at a final solution of the problem involved, but the present study does throw some light upon the improvement for the analysis of wind speed data.On investigation of the characteristics of often-used probability curves, the type Ⅲ of Pearson frequency curves is finally adopted as it closely represents the law of distribution of the annual extreme wind speeds.All the formulas for determining basic wind loads have been carefully reviewed and a set of new formulas applicable to different regions in China is prepared.After a vigorous study on the papers written by the Soviet and the Chinese scientists, the authors have derived an optimum wind-load coefficient for China—it is based on the gust factor, i.e. the ratio of peak gust to the mean.10-minute wind.A Chart of the distribution of basic wind loads of China has been mapped out and some brief geographical and climatological accounts are also given.