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- Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese
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- Volume 57, Issue 3, 2015
Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - Volume 57, Issue 3, 2015
Volumes & issues
Volume 57, Issue 3, 2015
Evaluation of the effect of deteriorating riding quality on bus-pavement interaction : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 57, pp 2 –8 (2015) http://dx.doi.org/http://dx.doi.org/10.17159/2309-8775/2015/v57n3a1More Less
Deteriorating riding quality has a negative impact not only on infrastructure, but on the road user as well. Road users experience higher vehicle operating costs (VOCs), longer travel times, congestion and uncomfortable rides, to name a few. The purpose of this paper is to demonstrate the link between deteriorating riding quality and high vertical accelerations (awz) and VOCs for a bi-articulated bus on an identified bus route with different responsible road authorities in rural Mpumalanga, South Africa. The link, as identified, indicated that the speed the bus travelled played a big role in the generation of awz. Recommendations for future research are also proposed.
Comparison of two data-driven modelling techniques for long-term streamflow prediction using limited datasets : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 57, pp 9 –17 (2015) http://dx.doi.org/http://dx.doi.org/10.17159/2309-8775/2015/v57n3a2More Less
This paper presents an investigation into the efficacy of two data-driven modelling techniques in predicting streamflow response to local meteorological variables on a long-term basis and under limited availability of datasets. Genetic programming (GP), an evolutionary algorithm approach and differential evolution (DE)-trained artificial neural networks (ANNs) were applied for flow prediction in the upper uMkhomazi River, South Africa. Historical records of streamflow, rainfall and temperature for a 19-year period (1994-2012) were used for model design, and also in the selection of predictor variables into the input vector space of the model. In both approaches, individual monthly predictive models were developed for each month of the year using a one-year lead time. The performances of the predictive models were evaluated using three standard model evaluation criteria, namely mean absolute percentage error (MAPE), root mean-square error (RMSE) and coefficient of determination (R2). Results showed better predictive performance by the GP models (MAPE: 3.64%; RMSE: 0.52: R2: 0.99) during the validation phase when compared to the ANNs (MAPE: 93.99%; RMSE: 11.17; R2: 0.35). Generally, the GP models were found to be superior to the ANNs, as they showed better performance based on the three evaluation measures, and were found capable of giving a good representation of non-linear hydro-meteorological variations despite the use of minimal datasets.
Performance assessment of aquatic macrophytes for treatment of municipal wastewater : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 57, pp 18 –25 (2015) http://dx.doi.org/http://dx.doi.org/10.17159/2309-8775/2015/v57n3a3More Less
The objective of the study was to evaluate the performance of three different aquatic macrophytes for treatment of municipal wastewater collected from Taxila in Pakistan. A physical model of a typical treatment plant was constructed and was operated for six experimental runs with each species of macrophyte. Every experimental run consisted of a thirty-day period. Regular monitoring of influent and effluent concentrations were made during each experimental run. Locally available macrophyte species (water hyacinth, duckweed and water lettuce) were selected for testing. To evaluate the treatment performance of each macrophyte, BOD5, COD, and nutrients (nitrogen and phosphorus) were monitored in the effluent from the model at different detention times for each experimental run, after having ensured steady state conditions. The average reduction of effluent value for each parameter, using water hyacinth, was 50.61% for BOD5, 46.38% for COD, 40.34% for nitrogen and 18.76% for phosphorus. For duckweed, the average removal efficiency for the selected parameters was 33.43% for BOD5, 26.37% for COD, 17.59% for nitrogen and 15.25% for phosphorus, and for water lettuce the average removal efficiency was 33.43% for BOD5, 26.37% for COD, 17.59% for nitrogen and 15.25% for phosphorus. The mechanisms of pollutant removal in this system include both aerobic and anaerobic microbiological conversions, sorption, sedimentation, volatilisation and chemical transformations. The rapid growth of the biomass was measured within the first ten days of the detention time. It was also observed that performance of macrophytes is influenced by variations in pH and temperature. A pH of 6-9 and temperature of 15-38°C is most favourable for treatment of wastewater by macrophytes. The option of macrophytes for treatment of municipal sewage under local environmental conditions can be explored by further verifying the removal efficiency under different environmental conditions.
Evaluation of the response behaviour of unconfined cemented materials under dynamic loading : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 57, pp 26 –34 (2015) http://dx.doi.org/http://dx.doi.org/10.17159/2309-8775/2015/v57n3a4More Less
There is a significant increase in traffic loading on most roads in the developing African countries, and South Africa is one of them. Often this increased traffic loading results in the premature failure of pavement structures. Mechanistic-empirical (M-E) design methods based on fundamental principles are better able to accommodate changes in the design environment. The successful use of design methods depends on the accuracy of the input material parameters. Therefore, as design is moving towards M-E design methods, there is a need for the material parameters to reflect the actual pavement response to dynamic loads. The objective of this paper is to report on the investigation of the response of cement-stabilised sub-base layers to dynamic load by evaluating stiffness at a known strain level. This stiffness was compared with those derived from unconfined compressive strength (UCS) tests performed at static load. The strain and stiffness values were also evaluated against compacted density, cement content, moisture content and material type. It was found that stiffness of some of the cement-stabilised sub-base layers may possibly be overestimated through the use of static loads.
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 57, pp 35 –43 (2015) http://dx.doi.org/http://dx.doi.org/10.17159/2309-8775/2015/v57n3a5More Less
The objective of urban transportation planning is, or should be, to optimise the access to opportunities for all people. One of the factors that defines access is to minimise the travel time between home and both primary and secondary activities. Optimisation refers to the balance between the benefits of reducing travel time with the cost of that reduction. Cost includes operational, infrastructure and environmental costs. However, the reality in many cities is that travel time is often minimised for some users or communities, while it remains relatively high for others.
This paper explores the core components of travel time of an integrated public transport system, and compares that with travel time in the private transport system. This is done by using travel time data for Cape Town to estimate the value of time spent on each component of a typical trip in Cape Town in 2013.
The paper concludes that travelling by public transport takes significantly longer than by private car for the average trip in Cape Town. It then highlights where to focus investment in the public transport system to move towards an integrated, multi-modal system that can compete with the private car, and thereby become attractive to all communities.
Finite element analyses of the structural behaviour of pylons supporting an inclined coal conveyor : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 57, pp 44 –56 (2015) http://dx.doi.org/http://dx.doi.org/10.17159/2309-8775/2015/v57n3a6More Less
As part of the coal conveyance system at Medupi Power Station, an inclined coal conveyor will transport coal from the stockyard to the coal transfer tower, and from there to the boilers. The conveyor is supported by concrete columns (pylons), in turn supporting the steel gantries on which the conveyor is located. The pylons can be considered as cantilever columns during the construction stage, while in the final operational stage with the steel gantries positioned in-between the pylons, a frame system will be formed. The gantries are connected to the pylons with custom-designed sliding joints, which allow limited movement of the gantries in the longitudinal direction of the conveyor. This paper describes how various finite element analyses of the structural behaviour of the pylons and the overall structure of the inclined coal conveyor were undertaken to assess wind and seismic actions. It focuses on modelling the behaviour of the concrete pylons during the construction period, a comparison between finite element models (FEMs) with different complexities and the implications of simplifying the FEMs. It will be shown that the simplified beam element models provide adequate modelling of the structural behaviour for this kind of structure. The modelling of non-linear connections between elements for static and dynamic conditions was also investigated, as well as the influence of the sliding joints between the pylons and the gantries on the overall behaviour of the structure. It will be shown that the overall behaviour of the structure can be highly influenced by the action of the sliding mechanism and that the force distribution between the structural members can differ significantly. Recommendations on how to approach the modelling of this type of structure are made.
It is concluded that the simplified model can be used to capture the behaviour of the structure, as well as the complex sliding joint mechanism, which has a major influence on the performance of the structure and the force distribution in the structural system.
Investigating the bottom free surface nappe (ogee profile) across a sharp-crested weir caused by the flow in an asymmetrical approach channel : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 57, pp 57 –63 (2015) http://dx.doi.org/http://dx.doi.org/10.17159/2309-8775/2015/v57n3a7More Less
The shape of an ogee spillway is based on the shape of the lower nappe of water flowing over an aerated sharp-crested weir. At the design discharge, this shape minimises the possibility of sub-atmospheric pressure occurring on the spillway and maximises the discharge across the spillway. The formulae that are currently in use to approximate the ogee profile consider only two-dimensional flow parameters, being the depth of flow over the spillway crest, the inclination of the upstream wall face, and the pool depth upstream of the spillway. The current formulae for the ogee shape, does not consider the influence of three-dimensional flow. The most significant three-dimensional flow parameters that could affect the shape of the lower nappe are the flow velocity distribution upstream of the spillway, the orientation or angle of the water approaching the spillway, the asymmetrical cross-section of the approach channel, and the curvature of the dam wall. This paper reflects the influence of asymmetrical flow in the approach channel. The investigation was based on a physical model constructed at the Department of Water and Sanitation (DWS). The inclination of the model's sidewalls of the upstream approach channel was varied to cause a change in the symmetricity, while the lower nappe profile was routinely measured. It was found that the flow in the asymmetrical approach channel caused a variation from the theoretical estimated ogee profile. A comparison between the measured nappe profile and the currently used formulae was investigated. It can be concluded that the symmetricity of the approach channel influences the shape of the bottom nappe, which differs from the shape as proposed by the current ogee formulae. It is recommended that three-dimensional flow should be examined when designing an ogee spillway.