Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> vol. 57 num. 4 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>Delay and queue lengths at stop/go control during half-width construction</b>]]> It is common practice in South Africa that road reseal projects, road reconstruction projects or road upgrade projects on two-lane, two-way roads are constructed in half-widths, resulting in a situation where traffic on the remaining roadway is reduced to one-way operation. There is currently no method for determining a suitable length of work zone for half-width construction based on traffic volumes, and also no method for determining waiting time for the vehicle in the front of the stationary queue at the STOP/GO control, and of the back-of-queue position at such a work zone. An Excel-based calculation sheet for determining the back-of-queue position and the maximum waiting time, was developed. This was used to develop design tables, graphs and equations that can be used by designers and contractors to estimate the back-of-queue position and maximum waiting time. Based on the conclusions of this paper and the fact that this project was largely based on literature studies of traffic conditions not related to work zones for half-width construction, the main recommendation of the study is that all the input parameters which were investigated need to be verified and calibrated specifically for work zones for half-width construction. <![CDATA[<b>Perceptions of professional practitioners and property developers relating to the costs of green buildings in South Africa</b>]]> Sustainable design practices are a key component in ensuring that the building and civil infrastructure industry does not damage our natural environment. Green buildings - and allied initiatives in other sectors of the built environment - are a primary mover in promoting sustainable design practices. An important and dangerous inhibitor of sustainable design practices, however, is the perception among key decision-makers that the additional costs of green - or sustainably designed - buildings are too high, and that they are therefore not economically viable. This study tested what those perceptions are, and compared the results to (limited) actual cost data and found that the cost premium is less than half of what most decision-makers think it is. Recommendations are then made around the development of awareness programmes at both undergraduate and postgraduate levels, the need to highlight the necessity for developing further and more accurate data related to green building costs, and the need to establish incentives to drive the take-up of sustainable design practices. <![CDATA[<b>Effect of paste content on the properties of high-strength concrete pavements</b>]]> Ultra-thin continuously reinforced concrete pavement (UTCRCP) is an innovative pavement type that has the potential to fulfil South Africa's pavement repair strategy requirements. Premature failure in UTCRCP is linked to the formation of cracks that allow water ingress into supporting layers. Environmental conditions, as well as concrete properties, determine the concrete cracking tendency. Concrete properties are a function of the mixture proportions, and unlike environmental conditions, mixture proportions are controllable. The effect of mixture proportions on the properties of high-strength concrete (HSC) used in UTCRCP should be investigated. The objective of this research was to study the influence of paste content on the properties of HSC used in UTCRCP. Two sets of concrete were tested. The paste content of the first set was varied from 23% to 37% by mass, using multivariable analysis in conjunction with superplasticiser (SP) dosage. The paste content of the second set was varied from 25% to 60% by mass, only varying SP dosage to control the workability. The multivariable analysis revealed that, within the parameter range tested, paste content influenced early-age properties, but not long-term properties. Through variation of the paste content over a wider range during the second set it was found that paste content does influence both the early-age and long-term properties of HSC. From the results it could be seen that increasing the paste content of HSC generally has a detrimental effect. The paste content of HSC used in UTCRCP should be minimised, while maintaining a reasonable workability. <![CDATA[<b>Design aspects of concrete towers for wind turbines</b>]]> All over the world an increase in the use of renewable energy sources is being sought, and here the utilisation of wind energy plays an important role. Germany currently represents one of the world's largest markets for wind energy. At the end of 2013, nearly 24 000 onshore wind turbines with a total output of approximately 34 000 MW had been installed in Germany. Hub heights of up to 140 m and outputs of 3 to 4 MW are now no longer unusual features of new onshore wind turbines. The focus of this paper is on concrete support structures for wind turbines. Different concrete tower concepts are presented, and the influence of the construction method on the design and verification processes is described. In particular, the text deals with the eigenfrequency analysis, as well as the bearing, shear and torsional resistances of concrete towers. The differences between cast-in-place and precast towers are listed. <![CDATA[<b>Dynamic behaviour of normally reinforced concrete wind turbine support structures</b>]]> Transportation logistics of large steel towers have led to concrete towers becoming a viable option. There are currently no design codes dealing exclusively with the design of concrete wind turbine towers. Wind turbine towers have strict constraints on the fundamental frequency of the tower to avoid resonance. This paper investigates the dynamic behaviour of wind turbine towers using nonlinear finite element modelling. Focus is placed on the effect of crack formation and soil stiffness on the fundamental frequency of the tower. An analytical model is then proposed that can be used in the primary design stage to determine the geometry of the tower that satisfies the fundamental frequency requirements. <![CDATA[<b>A study on the design and material costs of tall wind turbine towers in South Africa</b>]]> The aim of this project was to study the structural design and material costing of various designs of tall wind turbine towers and the associated foundations in a South African context. Design guidelines are proposed for the design of tubular steel, concrete and concrete-steel hybrid towers and foundations for hub heights of 80, 100 and 120 m. The results indicate that concrete and hybrid towers become viable alternatives to the conventional steel towers at hub heights equal to and above 100 m. Three heights - 80 m, 100 m and 120 m - of each type of tower (steel, concrete and hybrid) and their foundations were designed according to the relevant design standards. The designs were verified using the Abaqus CAE finite element software (SIMULIA 2010). The material costs of the designs were calculated for a South African environment, according to the increases in material cost with increasing hub height. In this paper, the required foundation sizes for the concrete and hybrid towers were found to be smaller than for the steel towers. The material costs of the concrete and hybrid towers were shown to be lower than for the steel towers, especially at hub heights above 100 m. An increase in hub height caused an increase in energy generation of 3.52% and 6.28% for 80 m to 100 m, and for 80 m to 120 m hub heights, respectively. It is postulated that the concrete and hybrid towers become viable alternatives to the conventional steel towers at hub heights above 100 m. <![CDATA[<b>Chloride conductivity testing of concrete - past and recent developments</b>]]> The chloride conductivity index (CCI) is a quality control parameter used to assess the resistanc of concrete to chloride ingress. It is determined from the chloride conductivity (CC) test which has been in use in South Africa for close to two decades. During this time, it has undergone a number of changes to improve on its robustness, reproducibility, and repeatability. Plans are now under way to incorporate the test and other durability index tests (oxygen permeability and water sorptivity) into the SANS standards, and it is important that the end user is aware of the changes and why they were made. Specifically, aspects concerning a new design of the CC testing rig which is already in use, and a modified old design which is still being used in some laboratories, are highlighted, such as the significant but variable differences in CCI results that could occur between the old and new CC test rigs. Experimental investigations were carried out to establish the cause of these differences, which was identified as largely due to possible incomplete filling of the original device. Modifications were therefore made to the old CC test rig to ensure that both the new and the modified CC test rigs give similar results.