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Volume 58, Issue 3, 2016
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 58, pp 2 –12 (2016) http://dx.doi.org/10.17159/2309-8775/2016/v58n3a1More Less
Shell structures show several unique structural attributes, which promote their use when material and economic efficiency is required. The principal advantage of shells is that forces are largely transferred through in-plane action (i.e. axial forces), with only limited bending and shear forces. This has endorsed the use of unreinforced shells which can been designed through numerous methodologies - i.e. thrust line analysis (O'Dwyer 1999), shell theory (Farshad 1977), finite element analysis (Ramm & Mehlhorn 1991) and numerous physical modelling techniques - to ensure that only compressive stresses exist in the structure. Of specific discussion in this paper are the shells of the Mapungubwe Interpretation Centre, which are built exclusively from unreinforced earth tiles. Because the shells are unreinforced and earth tiles are susceptible to tension cracking, the shape of the structure and the construction practice are of paramount importance. Unfortunately, the Mapungubwe shells have cracked extensively, most notably at the openings. The causes of this cracking have been postulated in order to propose principles of good practice in designing and constructing unreinforced masonry shells. These guidelines were identified as follows: lips and eyebrows at shell openings should be avoided, shells should be unrestrained against expansion and contraction, and openings at the base should be of a catenary shape to match the flow path of compressive stress.
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 58, pp 13 –20 (2016) http://dx.doi.org/10.17159/2309-8775/2016/v58n3a2More Less
The main purpose of this study was to model the response of piles during a lateral load test conducted at RPC in Concón in 2006 by using simplified theoretical methods and the software Plaxis 2D, Cype, and GGU-Latpile. The piles were the longest built in Chile at the time of the test. This article contains the test description, a geotechnical characterisation and the theoretical fundamentals that support the different methods used for modelling the test. The results of the different models are also presented here. It is concluded that results obtained by simplified methods may be efficient in the early stages of a project and that accurate approximations can be achieved by using design software for continuous elements in the design of isolated elements.
Experimental investigation of local scour around circular bridge piers under steady state flow conditionsSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 58, pp 21 –27 (2016) http://dx.doi.org/10.17159/2309-8775/2016/v58n3a3More Less
Local scour around bridge piers is one of the main causes of bridge failures. In this study, scour depths and scour hole geometries around circular bridge piers were investigated under clear water scour conditions for various flow rates. The experiments were carried out in a rectangular flume 80 cm wide, 18.6 m long and 75 cm high by using uniform sediment with a median diameter of 1.63 mm and geometric standard deviation of 1.3. The flow rates and approach flow depths were measured with an electromagnetic flow meter and ultrasonic level sensors, respectively. A new empirical equation for the determination of scour depth is proposed based on the experimental findings of the present study and on experimental data available in the literature. The experimental results were also compared with those calculated using several empirical equations developed by previous studies. The proposed new equation to predict scour depth around a circular bridge pier was evaluated in terms of determination co-efficient (R2) and scatter index (SI). The Fisher (f) test was also applied to test the statistical significance of the proposed equation.
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 58, pp 28 –36 (2016) http://dx.doi.org/10.17159/2309-8775/2016/v58n3a4More Less
In this study a dynamic analysis of a 77-year-old single-span steel truss railway bridge was carried out. The study was approached by three different methods - field measurement, modal analysis using a three-dimensional finite element model of the bridge, and a simple generalised single degree of freedom (SDOF) analysis. Field measurement was conducted using accelerometers and displacement transducers, which were mounted on special sections fixed to an adjacent bridge. The finite element models of the bridge were prepared using beam and shell elements. The dynamic responses studied include the displacement, acceleration and natural frequency of the bridge. The results showed that the generalised SDOF model, with simple addition of the effects of each axle, provided reasonably accurate displacements compared to the measured values. The generalised SDOF model, finite element model with beam elements and finite element model with shell elements also gave reasonably accurate estimates for the natural frequency of the bridge.
Productivity management in the South African civil construction industry - factors affecting construction productivitySource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 58, pp 37 –44 (2016) http://dx.doi.org/10.17159/2309-8775/2016/v58n3a5More Less
Labour productivity in South Africa is at one of its lowest levels. During 2014 the civil construction industry contributed only 3.5% to the GDP of South Africa. It is faced with challenges such as an industry environment that is increasingly competitive, and organisations in the civil industry that experience financial difficulties, such as low profit margins. An industry specific survey, using a questionnaire, was conducted to ascertain the perceptions of industry professionals regarding factors which have an impact on productivity. A literature study was done to identify the factors that have an impact on construction productivity, based on a global perspective. From the literature study, 12 studies were identified, and a benchmark was set with which to compare the findings of the research questionnaire.To obtain the relevant information through the questionnaire, a selective sampling process was used, as the focus of the research required a specific group of individuals who were involved in the management of projects in the civil construction industry. Two civil engineering organisations, the South African Forum of Civil Engineering Contractors and the South African Institution of Civil Engineering, were contacted to assist with the distribution of the questionnaire. The questionnaire consisted of 51 factors which the industry professionals had to rate, based on their experience. These factors had to be rated with the use of a 0-4 Likert scale, based on two specific questions: (1) What impact does the factor have on construction productivity? (2) What is the frequency of occurrence of the factor? A total of 40 questionnaires were completed by the industry professionals. Thereafter the ranking of the factors was calculated with the use of the relative importance index.
Publishing particulars of the paper under discussion - the identification and treatment of poor durability Karoo dolerite base course aggregate - evidence from case studies : discussionSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 58, pp 45 –46 (2016) http://dx.doi.org/10.17159/2309-8775/2016/v58n3a6More Less
Table 1 (referencing COLTO 1998) of the above-mentioned technical paper incorrectly states that the PI shall be < 12 when the PI is determined on the -0.075 mm fraction because -0.425 mm fraction is non-plastic. COLTO requires that the PI of the -0.075 mm fraction shall not exceed 12 without any qualification. If the PI exceeds 12, the material shall be chemically modified. After chemical modification the PI of the -0.075 mm fraction shall not exceed 8. The Technical Committee involved in the COLTO 1998 edition based these criteria.