Journal of the South African Institution of Civil Engineers
The accurate estimation of strong winds is of cardinal importance to the built environment, parti... more The accurate estimation of strong winds is of cardinal importance to the built environment, particularly in South Africa, where wind loading represents the dominant environmental action to be considered in the design of structures. While the Gumbel method remains the most popular applied method to estimate strong wind quantiles, several factors should influence the consideration of alternative approaches. In South Africa, the most important factors influencing the choice of method are the mixed strong wind climate and the lengths of available wind measurement records. In addition, the time-scale of the estimations (in this case one hour and 2-3 seconds) influences the suitability of some methods. The strong wind climate is dominated by synoptic scale disturbances along the coast and adjacent interior, and mesoscale systems, i.e. thunderstorms, in the biggest part of the interior. However, in a large part of South Africa more than one mechanism plays a significant role in the develop...
Journal of the South African Institution of Civil Engineers
Although wind is the most important environmental action on buildings and structures in South Afr... more Although wind is the most important environmental action on buildings and structures in South Africa, the last comprehensive strong wind analysis was conducted in 1985. The current wind loading code is still based on the strong wind quantiles forthcoming from that analysis. Wind data available for strong wind analysis has increased about five-fold, due to the employment of automatic weather station (AWS) technology by the South African Weather Service. This makes an updated assessment of strong winds in South Africa imperative. Based on the estimation of strong winds as reported in the accompanying paper (see page 29 in this volume), the spatial interpolation of 50-year characteristic strong wind values to provide updated design wind speed maps is reported in this paper. In addition to taking account of short recording periods and the effects of the mixed strong wind climate, the exposure of the weather stations was considered and correction factors applied. Quantile values were adj...
On 21 October 1999, a severe thunderstorm developed over areas 50 km south of Johannesburg. This ... more On 21 October 1999, a severe thunderstorm developed over areas 50 km south of Johannesburg. This weather system produced a large tornado (F3 on the FP scale) which crossed the Heidelberg farming district (between Vanderbiljpark and Secunda). Relatively little damage occurred, but there were minor injuries and damage to property. In this paper the event is analyzed by means of all available observation data, including conventional radar data which showed significant reflectivities as well as good reflectivity gradient. The authors also made use of the 0 and 6 h fields of the local version of the Eta model (48 km resolution) in order to supplement the sparse data coverage over the country. Indications of instability and shear were analyzed on plan view as well as by means of model soundings. Several indicators of severe weather and possible tornadic activity could be found. Although only a few tornadoes occur every year in South Africa, these events cause damage and loss of life. It i...
ABSTRACT Wind constitutes one of the major environmental factors affecting the design and perform... more ABSTRACT Wind constitutes one of the major environmental factors affecting the design and performance of built environment. Each country has its unique climatic wind conditions, and the way in which these are considered and implemented in the structural design, is important. An implementation or adoption of any new engineering design stipulations introduces a formidable challenge to the developers of the standards and the design profession. This has been experienced in some of the countries (e.g. the UK, Australia and the USA), where processes of modernising the outdated codification took place in the past. Although both Poland and South Africa are currently at the early implementation stage of the new wind loading design stipulations, there is a major difference between the circumstances of the two countries. Poland, as an EU member state, has a compulsory obligation to adopt the new uniform standarisation requirements, within a stipulated time-frame. The South African code developers, after a thorough investigation process which will be highlighted in the paper, decided voluntarily to adopt the Eurocode as the primary model document
Copyright: 2010 Techno Press. This is the pre-print version of the work. The definitive version i... more Copyright: 2010 Techno Press. This is the pre-print version of the work. The definitive version is published in Wind and Structures Journal, Vol 31(1), pp 37-55 In this paper South Africa is divided into strong wind climate zones, which indicate the main sources of annual maximum wind gusts. By the analysis of wind gust data of 94 weather stations, which had continuous climate time series of 10 years or longer, six sources, or strong-wind producing mechanisms, could be identified and zoned accordingly. The two primary causes of strong wind gusts are thunderstorm activity and extratropical low pressure systems, which are associated with the passage of cold fronts over the southern African subcontinent. Over the eastern and central interior of South Africa annual maximum wind gusts are usually caused by thunderstorm gust fronts during summer, while in the western and southern interior extratropical cyclones play the most dominant role. Along the coast and adjacent interior annual extr...
Journal of the South African Institution of Civil Engineers
The accurate estimation of strong winds is of cardinal importance to the built environment, parti... more The accurate estimation of strong winds is of cardinal importance to the built environment, particularly in South Africa, where wind loading represents the dominant environmental action to be considered in the design of structures. While the Gumbel method remains the most popular applied method to estimate strong wind quantiles, several factors should influence the consideration of alternative approaches. In South Africa, the most important factors influencing the choice of method are the mixed strong wind climate and the lengths of available wind measurement records. In addition, the time-scale of the estimations (in this case one hour and 2-3 seconds) influences the suitability of some methods. The strong wind climate is dominated by synoptic scale disturbances along the coast and adjacent interior, and mesoscale systems, i.e. thunderstorms, in the biggest part of the interior. However, in a large part of South Africa more than one mechanism plays a significant role in the develop...
Journal of the South African Institution of Civil Engineers
Although wind is the most important environmental action on buildings and structures in South Afr... more Although wind is the most important environmental action on buildings and structures in South Africa, the last comprehensive strong wind analysis was conducted in 1985. The current wind loading code is still based on the strong wind quantiles forthcoming from that analysis. Wind data available for strong wind analysis has increased about five-fold, due to the employment of automatic weather station (AWS) technology by the South African Weather Service. This makes an updated assessment of strong winds in South Africa imperative. Based on the estimation of strong winds as reported in the accompanying paper (see page 29 in this volume), the spatial interpolation of 50-year characteristic strong wind values to provide updated design wind speed maps is reported in this paper. In addition to taking account of short recording periods and the effects of the mixed strong wind climate, the exposure of the weather stations was considered and correction factors applied. Quantile values were adj...
On 21 October 1999, a severe thunderstorm developed over areas 50 km south of Johannesburg. This ... more On 21 October 1999, a severe thunderstorm developed over areas 50 km south of Johannesburg. This weather system produced a large tornado (F3 on the FP scale) which crossed the Heidelberg farming district (between Vanderbiljpark and Secunda). Relatively little damage occurred, but there were minor injuries and damage to property. In this paper the event is analyzed by means of all available observation data, including conventional radar data which showed significant reflectivities as well as good reflectivity gradient. The authors also made use of the 0 and 6 h fields of the local version of the Eta model (48 km resolution) in order to supplement the sparse data coverage over the country. Indications of instability and shear were analyzed on plan view as well as by means of model soundings. Several indicators of severe weather and possible tornadic activity could be found. Although only a few tornadoes occur every year in South Africa, these events cause damage and loss of life. It i...
ABSTRACT Wind constitutes one of the major environmental factors affecting the design and perform... more ABSTRACT Wind constitutes one of the major environmental factors affecting the design and performance of built environment. Each country has its unique climatic wind conditions, and the way in which these are considered and implemented in the structural design, is important. An implementation or adoption of any new engineering design stipulations introduces a formidable challenge to the developers of the standards and the design profession. This has been experienced in some of the countries (e.g. the UK, Australia and the USA), where processes of modernising the outdated codification took place in the past. Although both Poland and South Africa are currently at the early implementation stage of the new wind loading design stipulations, there is a major difference between the circumstances of the two countries. Poland, as an EU member state, has a compulsory obligation to adopt the new uniform standarisation requirements, within a stipulated time-frame. The South African code developers, after a thorough investigation process which will be highlighted in the paper, decided voluntarily to adopt the Eurocode as the primary model document
Copyright: 2010 Techno Press. This is the pre-print version of the work. The definitive version i... more Copyright: 2010 Techno Press. This is the pre-print version of the work. The definitive version is published in Wind and Structures Journal, Vol 31(1), pp 37-55 In this paper South Africa is divided into strong wind climate zones, which indicate the main sources of annual maximum wind gusts. By the analysis of wind gust data of 94 weather stations, which had continuous climate time series of 10 years or longer, six sources, or strong-wind producing mechanisms, could be identified and zoned accordingly. The two primary causes of strong wind gusts are thunderstorm activity and extratropical low pressure systems, which are associated with the passage of cold fronts over the southern African subcontinent. Over the eastern and central interior of South Africa annual maximum wind gusts are usually caused by thunderstorm gust fronts during summer, while in the western and southern interior extratropical cyclones play the most dominant role. Along the coast and adjacent interior annual extr...
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