Wind climatology of South Africa relevant to the design of the built environment

[摘要] ENGLISH ABSTRACT: In South Africa, wind constitutes the most critical environmental loading affecting thedesign of the built environment. The wind climatic information, which is currentlyincorporated in structural design standards, is based on the analysis of records from alimited number of wind recording stations, mainly located in large cities, and was doneseveral decades ago. In view of the size and the climatological diversity of South Africa,this information cannot be deemed to be adequate. Therefore, the incorporation of welldistributedand updated information on wind climate is essential. The present studyendeavoured to address this issue. A strong wind climatology was developed with theuse of observed climate data, with the most significant result that a mixed strong windclimate is prevalent in the greater part of South Africa. Statistical approaches toestimate extreme wind speeds were investigated with applicable wind data, with theoptimum approach guided by the unique climatological environment and the statisticalproperties of the utilised data set: For the wind gust analysis the Peak-Over-Thresholdmethod with the exponential distribution is recommended, while in a mixed strong windclimate the 'mixed climate approach is preferred. For the analysis of the hourly meanwind speeds the choice is between the Gumbel distribution and the mixed climateapproach, depending on the strong wind climate. The estimation and incorporation ofenvironmental correction factors to the measured wind speeds were necessary as thesurroundings of most weather stations did not correspond to the reference TerrainCategory. For some of the weather stations it was impossible to compensate for theinadequate exposure and surrounding complex topography, so that a reduced numberof weather stations were available for the strong wind analyses. The values estimatedfor the design wind speeds, adjusted for the short lengths of data records, as well astechniques developed to guide the spatial interpolation of the quantiles, were utilised todevelop updated maps of the regional design wind speeds. A comparative studybetween the results of this study, and that of the previous study on which the currentloading code in South Africa is based, indicates that the present study should producemore reliable quantile estimations.

[发布机构] Stellenbosch University