Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> vol. 57 num. 1 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Capacity self-assessment as a catalyst for improved municipal service delivery</b>]]> This research paper illustrates that accurate and truthful capacity assessments are a fundamental phase of any capacity building process, and that capacity assessments play a fundamental role in reaching the necessary performance efficiency. Service delivery performance enhancements by municipalities are becoming increasingly necessary. At the same time, however, the majority of municipalities in South Africa find themselves under-capacitated. Some municipalities are aware of the lack of capacity within their organisation, but are unable to identify, define and quantify these shortcomings. Many other municipalities are not aware of their capacity shortfalls. In both cases, this is often caused by the lack of necessary systems and procedures to assess the different dimensions of organisational capacity. In this regard, this research paper introduces a proposed Subjective Municipal Capacity Self-Assessment Model (SMCSAM) as an alternative solution to the current practices of the Municipal Demarcation Board. It is intended that this model be used internally by municipalities to sustain internal capacity building and performance enhancement initiatives. <![CDATA[<b>Review of current methods for estimating areal reduction factors applied to South African design point rainfall and preliminary identification of new methods</b>]]> Design point rainfall estimates assume a uniform distribution of rainfall over a catchment, and hence are only representative for a limited area. For larger areas, areal reduction factors (ARFs) are used to convert design point rainfall depths/intensities to an average areal design rainfall depth/intensity for a catchment-specific critical storm duration and catchment area. This paper presents a review of ARF estimation methods used nationally and internationally, with comparisons of the South African methods in the C5 secondary drainage region using standard input variables. The comparison of different ARF estimation methods confirmed that the empirical methods adopted for general use in South Africa are based on a limited database of observed rainfall data and are used without local correction factors beyond their original developmental regions. This results in the characterisation of the actual rainfall process over a catchment, and translation into questionable design peak discharge estimates. Therefore, the ARFs in South Africa need to be re-investigated in the light of recent extreme flood events, utilising the longer periods of record and denser rain-gauge networks which are now available for analysis. The variation of ARFs with return period and with rainfall producing mechanisms also needs to be investigated. Updated ARFs developed and verified using local rainfall data will improve the accuracy of design hydrology for large catchments in South Africa when event-based rainfall-runoff deterministic methods are used. <![CDATA[<b>Revised test protocols for the identification of dispersive soils</b>]]> Dispersive soils are prevalent in many areas of South Africa, and the presence of these soils has always posed a problem on road construction sites. The use of dispersive soils in roadway embankments and structures can lead to serious engineering problems if the soils are not accurately identified before use and appropriate mitigation measures taken. The current identification methods include the pinhole, double hydrometer, crumb and chemical tests, which are commonly used in combination to obtain the most reliable outcome. These laboratory tests, however, have not always been entirely consistent, whether used in combination or individually, and it is possible that the reason lies in the actual testing procedures. This paper discusses the observations made during a detailed investigation into the current methods used for testing and identification of dispersive soils. The test methods were thoroughly analysed and shortcomings identified. The differences resulting from different test techniques are examined and solutions to overcome the problems proposed. The paper concentrates mainly on the modification of the physical tests. The recommended solutions and process of identification are also proposed. <![CDATA[<b>Structures subjected to startup and shutdown of rotating machinery</b>]]> With the advent of fast computers and easy-to-use software, transient dynamic analysis of structures has apparently become easy to perform. The engineer usually enters the entire structure (even in three dimensions) and produces results and plots that are sophisticated in appearance. The simulation results are most probably accepted without asking the following questions: "Are the results correct?" and "What is the sensitivity of the results to the various parameters?" The approach in this paper is different and more traditional: the salient behaviour of transient machinery during startup and shutdown is presented after studying the response of a structure which has been reduced to a single degree of freedom. The two-dimensional forces generated by rotating machinery during startup/shutdown have been derived analytically. Normalised curves have been computed to show the maximum response of the structure. A wide range of damping ratios has been considered. The maximum structural deflections during startup/shutdown can be significantly greater than the steady-state response and thus cannot be ignored. The normalised curves show that common approaches to limit dynamic deflections by increasing stiffness and/or damping have to be carefully considered during the transient regime. Two examples of an unbraced and a braced portal frame have been presented to demonstrate the practical use of these normalised curves. <![CDATA[<b>Concrete durability standards: International trends and the South African context</b>]]> Durability problems in reinforced concrete (RC) structures are an issue of global concern, since they threaten economic growth, natural resources and human safety. As a result, attempts have been made in design standards developed in most countries to include requirements to provide durable RC structures. This paper examines and compares such durability requirements in standards from the United States, Australia, Canada, Europe, India and South Africa. It focuses on aspects such as exposure conditions, limiting values of material compositions and proportions, and cover depth to the reinforcing steel. The paper describes issues behind prescriptive standards and deals with challenges confronting performance approaches for concrete durability. Following international trends, it is evident that the South African Standards, particularly SANS 10100-2, must undergo substantial updating and improvements to durability requirements. The paper suggests the means of re-drafting and implementing durability specifications in any revised version of SANS 10100-2, taking into account both prescriptive and performance alternatives. Further, a methodology of developing durability specifications suitable for the South African concrete industry is proposed, and recommendations are made for future developments. <![CDATA[<b>Mapping of soil layers using artificial neural network (case study of Babol, northern Iran)</b>]]> Over the last few years, artificial neural networks (ANNs) have been used successfully for modelling all aspects of geotechnical engineering problems. ANNs are a form of artificial intelligence which attempt to mimic the function of the human brain and nervous system. ANNs are well suited to model the complex behaviour of most geotechnical engineering problems. The purpose of this paper was to assess the layering of subsurface soil using ANNs. Assessing the structure of soil layers on a site, depending on the extent of the study area, requires drilling several boreholes and performing several tests which demand considerable time and money. Increasing the knowledge of soil layer properties between boreholes leads to improved understanding of the near-surface geology. ANNs learn from data examples presented to them in order to capture the subtle functional data relationships, even if the underlying relationships are unknown or the physical meaning is difficult to explain. This paper focuses on the information gathered from the boreholes in a range of 40 square kilometres of Babol City in the north of Iran. The data was collected and classified in order to determine the characteristics of the soil layers. To later classify the different layers at different depths and to determine the thickness of each layer at a specified depth, multi-layer neural networks were trained separately. To quantify the neural network performance in estimating the changes of soil layers, some data from the test boreholes was presented to the network for the first time, and the results of neural networks were compared with actual data obtained from site investigations. The results show a high degree of accuracy in prediction by ANN models. <![CDATA[<b>The effect of bedding errors on the accuracy of plate load tests</b>]]> During conventional plate load tests the stiffness of the ground is determined by measuring the settlement of a plate placed on the ground surface. If the contact between the plate and the ground is rough, bedding errors may occur during the test when plastic deformation occurs at the contacts between the plate and the ground. This paper addresses the effect of bedding errors on the accuracy of plate load tests. Three different surface preparation methods were investigated. In addition, a modified plate load test was designed to eliminate the effect of bedding errors that occur during these tests. Telescopic probes were used to measure the relative displacement at two points below the centre of the plate. The stiffness values, determined from the vertical displacement of the plate, were compared with the internal stiffness values determined by means of the telescopic probes. All stiffness values were compared with Continuous Surface Wave (CSW) measurements performed on the same material. The test apparatus, methods and results are discussed in this paper.