Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> vol. 59 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Review of climatic input data for wind load design in accordance with SANS 10160-3</b>]]> With the publication of Part 3 Wind Actions of the South African Loading Code SANS 10160:2010, several issues concerning adjustments from the reference standard Eurocode EN 1991-1-4:2004 could not be resolved due to lack of sufficient updated background information on South African conditions. The need for updating the map for the free field wind speed is related also to the improved representation of the mixed and complex strong wind climate of the country. Furthermore, strong wind probability models are used for the reliability assessment and calibration of wind design procedures. Updating of the reliability provisions for the revised wind loading process was a further need identified at the time. This paper provides a review of the historical development of the representation of the free field wind, used as input to design wind loading procedures for South Africa. The review considers: (i) the historical representations of the geographic distribution of free field wind, (ii) the climatic influences considered, and (iii) the probabilistic bases for the stipulated wind speed for the reliability provisions for design wind loads. On this basis, the background and motivation are provided for updating SANS 10160-3:2010. <![CDATA[<b>Development of an updated fundamental basic wind speed map for SANS 10160-3</b>]]> This paper evaluates the need for updating the strong wind climate stipulations of South Africa for the design of structures in accordance with SANS 10160-3:2010, as based on the latest information presented by Kruger et al (2013a; 2013b). The primary objective is to provide the geographic distribution of the characteristic gust wind speed by means of the fundamental value of the basic wind speed, stipulated as v b,0in SANS 10160-3. A reassessment of previously published information is made to incorporate additional wind speed modelling results and to investigate identified anomalies. The format of presentation, based on local municipal districts, is subsequently motivated, assessed and implemented. In order to provide for situations requiring the consideration of the dynamic effects of wind loading, similar information on characteristic hourly mean wind speed is provided. It is concluded that the presentation of wind speed on a district basis provides an effective balance between the spatial resolution of the available information and its use in operational standardised design. <![CDATA[<b>The effect of embedment on a foundation subjected to vertical vibration - a field study</b>]]> Design of machine foundations requires the prediction of the dynamic response of the foundation system at the frequencies of interest. The response is typically quantified in terms of a number of parameters that include the displacement, the dynamic stiffness, the resonant frequency, the amplitude at the resonant frequency and the natural frequency. The objective of this study was to investigate the vertical dynamic response of an embedded foundation experimentally. It was found that embedment increases the stiffness, damping and natural frequency of a foundation system, reduces the displacement and resonant amplitude, but that embedment has very little effect on the resonant frequency. <![CDATA[<b>Traffic characteristics and bridge loading in South Africa</b>]]> The loading model of the Technical Manual for Highways (TMH-7) published for bridge design in South Africa is in need of revision and simplification. The frequency of heavy vehicle loads has increased and the current application of the loading model is unnecessarily cumbersome. This paper aims to compare the heavy vehicle traffic loading of South Africa and Europe. A comparison of global internal bridge forces under the NA loading of TMH-7 and LM1 loading of Eurocode provides an indication of how current South African provision relates to the ones adopted in Europe. Above all, the traffic characteristics in South Africa are investigated in comparison to data used in development of LM1. LM1 loading generally results in higher internal forces when compared to TMH-7 loading. A direct adoption would thus imply more expensive bridges across South Africa without substantiation, considering the satisfactory past performance of existing structures. More importantly, the gross vehicle weights observed in South Africa are higher than those used for the development of LM1, indicating that the current TMH-7 distributed loading may be too low. Axle loads and their variability in South Africa are somewhat less than in Europe, so local design effects are less of a concern. It is apparent that further urgent work is required to establish a load model that reflects the current heavy vehicle traffic and predicts appropriate characteristic vertical loads. <![CDATA[<b>An investigation into the evidence of seasonal rainfall pattern shifts in the Western Cape, South Africa</b>]]> Climate change is a highly contentious topic in the modern world. There is much evidence to indicate that climatic shifts and extreme weather anomalies are taking place globally, in some places more than others. This paper presents the findings on research to determine whether shifts in seasonal rainfall patterns are indeed already visible in historical rainfall data in the Western Cape of South Africa. The paper aims to provide some baseline information which can stimulate further research in this field. Different analytical methods were formulated to investigate the relationships between daily rainfall indices over a set timescale. Data was collected from the South African Weather Service (SAWS) in order to accumulate 20 rainfall stations, each with at least 100 years of historical daily rainfall data. Statistical analysis, linear trend line distributions, time lag comparisons, cumulative distributions, moving average plots and autocorrelation relationships were applied to the data. The results of the analysis indicated that (1) the rainfall season undergoes fluctuations of wetter and drier years (approximately 20-year cycles), (2) the South Coast region exhibits a shift towards a longer rainfall season, and in contrast the Mediterranean region is shifting to a shorter rainfall season when linear trend lines were analysed, and (3) the moving average plots showed only isolated seasonal shifts at the boundary months. <![CDATA[<b>Application of metaheuristic algorithms to the improvement of the MyCiTi BRT network in Cape Town</b>]]> This paper discusses a design approach aimed at improving bus transit networks and their operations. In combining metaheuristic algorithms and a GIS procedure the paper shows how the level of network utilisation of a bus service can be improved. To achieve this goal, the procedure is applied to the design of a bus network. It is then, accordingly, compared with the current phase of the MyCiTi BRT network in the City of Cape Town, South Africa. The results indicate that the designed network performs better in terms of network utilisation and other operational parameters. It is hoped that this research will add value to the design and implementation of bus networks in Cape Town, together with their operation. <![CDATA[<b>An empirical preliminary prediction of heave</b>]]> The method described in the paper titled "Prediction of heave from the plasticity index and percentage clay fraction of soils" by Van der Merwe (1964) has been in common use since then. It predicts the potential heave due to the moisture change from a relatively dry state to a near-saturated state under a covered area, i.e. a maximum state change. In reality this may not always be the case, and this Note proposes an adaptation to the method whereby the probable change in moisture content is utilised in the calculation. This is determined by the in-situ moisture and the estimated equilibrium moisture content (EMC) derived from the liquid limit.