Theses and Dissertations (Civil Engineering)

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Deterioration models and market linked maintenance trigger based on big data for unpaved roads
(University of Pretoria, 2019-10) Maina, J.W. (James); Steyn, Wynand J.vdM.; tamryn.swanepoel@gmail.com; Swanepoel, Tamryn L.
The consumer perception is a growing concern for the fresh farm produce market as external damage reduces the likelihood of purchase and thus reduces the economic value to the retailer and grower. One of the major causes of mechanical damage to the surface of the fruit results from the vertical vibrations generated by the movement of haulage trucks on roads with high surface roughness. Although careful handling and well-designed packaging reduce the loss of fruits due to bruising, this can only be altered to a certain extent beyond which it becomes economically unfeasible and environmentally harmful to increase the number of protective packaging layers (Steyn et al., 2015). Experiments conducted by Pretorius and Steyn (2012) have shown that although the length of an unpaved road section forming part of the transportation route from the grower to the marketplace may be 40 times shorter than the length of the paved road section, the transported freight accumulates more damage over the short unpaved section than over the significantly longer, smoother paved section. Thus the quality of unpaved roads has a significant effect on the profitability of commercial farming. The deterioration of roads is governed by the behaviour of the material and the capacity of the drainage system under the combined actions of traffic and the environment (Paterson, 1987). Effective pavement management is a challenging task due to increased pavement deterioration and performance demands along with limited budget and human resources. Effective maintenance can take place when decision making is informed by knowledge of the current condition and expected future condition of the road which can be derived by analysing the historical performance of similar road segment types. Extensive historical road roughness data has been collected using a response type road roughness measuring system over a period of 16 months for various unpaved roads in Limpopo, South Africa. This project used the historical road roughness data, supplemented by maintenance history and rainfall data, to generate roughness deterioration models for unpaved road sections with varying characteristics by fitting various mathematical functions to the collected field data. Simple annual maintenance cost models were derived from the roughness deterioration models and used in conjunction with previously developed tomato shelf-life models to obtain optimum roughness thresholds for road sections with varying characteristics and tomatoes with varying degrees of ripeness. The classification of ripening tomatoes has been formally standardised by the United States Department of Agriculture into green, pink and red stages of ripeness. In general, greater deterioration occurred over the dry season with the most rapidly deteriorating road section type having a slope of greater than 6 per cent as well as relatively heavy traffic. Exponential models were found to be the most appropriate to model deterioration of the road condition over the dry season while linear models were best suited for modelling deterioration over the wet season using the road roughness as a condition indicator. The optimum roughness thresholds were highest for pink tomatoes and lowest for red tomatoes thus indicating that the lowest optimal maintenance expenditure is achieved when transporting red tomatoes while foregoing an extended shelf-life. The highest optimal shelf-life is reached when transporting pink tomatoes while incurring a greater maintenance cost. Thus, the results indicate that the optimum scheduling of maintenance activities on unpaved roads is dependent upon the demand of the product at the market. Greater demand for tomatoes will require a lower optimal shelf-life, thus the maintenance cost is minimised by transporting red tomatoes and scheduling maintenance activities using roughness triggers ranging between 4.4 m/km and 5.6 m/km (which is dependent upon the slope and traffic on the road section). Lower market demand will require a higher optimal shelf-life, thus the maintenance cost is minimised by transporting pink tomatoes while scheduling maintenance activities using roughness triggers ranging between 3.9 m/km and 4.4 m/km. The difference between these two scenarios results in an average shelf-life increase of 48 per cent while increasing the maintenance cost by an average of 82 per cent.
Development of a wake and backwater prediction approach for hydrokinetic turbines
(University of Pretoria, 2023-07) Van Dijk, Marco; Smith, Lelanie; Chantelniebuhr1@gmail.com; Niebuhr, Chantel Monica
Hydrokinetic turbine deployment in inland water reticulation systems holds untapped potential for future development in renewable energy. However, prior to implementation, it is crucial to understand the hydrodynamic effects associated with these devices. In particular, the flow fields effects prevalent in bounded subcritical flow regimes such as wake propagation and possible backwater effects. While a few analytical approximations for wake determination have been developed, most of them do not account for operational conditions in confined flow. Moreover, there is a lack of usable approaches for backwater determination in the existing literature. This limitation complicates the design and deployment process, leading to problematic installations and issues with regulatory procedures due to the numerous unknowns surrounding turbine deployment. This study focuses on developing a new semi-empirical model for the prediction of the wake generation and flow recovery which includes a study on metrics found to affect wake generation. Once the flow behaviour is well understood a generic and simplified method for calculating the backwater effect of HK turbines is tested. In this dissertation, data obtained from experimentally validated computational fluid dynamics (CFD) simulations provides a basis for the new simplified wake and backwater prediction approach. Among the available commercial software capabilities, Reynolds-averaged Navier-Stokes (RANS) models showed a strong correlation with turbine performance. A virtual disk model utilising the blade element momentum theory and employing Reynolds’s stress closure models was found to give the best representation of the wake and surrounding flow behaviour. The developed semi-empirical wake model performed well across various performance conditions (linked to the specific turbine thrust), ambient turbulence conditions, and blockage ratios. This model facilitates a reasonably accurate estimation of wake behaviour, enabling effective planning of turbine placement and spatial requirements for inland hydrokinetic schemes. The analytical backwater model developed in this study also demonstrated good correlation with experimental results. Its energy-based approach offers a simplified tool that can be easily incorporated into backwater approximations, also allowing for the inclusion of retaining structures as additional blockages. All models utilise only the flow characteristics and the turbine thrust coefficient, making them valuable tools for the initial analysis of wake and backwater effects resulting from the deployment of inland turbine system
Using early age concrete properties to determine setting time
(University of Pretoria, 2024-02-13) Kearsley, EP; Mostert, HF
When fresh concrete sets, it changes from a Bingham fluid to a solid, with strength and stiff-ness. Changes in concrete volume however starts taking place from the moment when water comes into contact with the cement, starting the hydration process. The chemical reaction be-tween the water and the cement cause shrinkage because the resulting product is smaller than the two reactants. The reaction is very slow in the beginning, but when it speeds up it causes an increased temperature that can result in an expansion of the mix. These volumetric changes increase in high strength concrete due to the reduced water/cement ratio, the increased cement content and the use of High Range Water Reducing Agents (HRWRA). It is important to know the exact setting time of concrete as volume changes that takes place after setting, will cause internal stresses, which could exceed the early age strength, resulting in the formation of cracks. Existing setting time test methods do not take into account the effect of changes in water/ce-ment ratio and concrete composition on the setting time. The aim of this study was to determine a setting time for concrete based on the point in time when the concrete starts behaving as a solid. A variety of test methods were used to determine and compare early age properties of concrete. The point in time when a rapid change in behaviour was observed was used as point from where early age shrinkage would have an effect on the stresses or strains that develops in the concrete. The measured shrinkage results were recorded from as soon as possible after casting but the influence of the shrinkage should be considered from this time onwards. The results of this investigation confirm that neither the initial nor final setting time typically recorded are representative of the time when the concrete starts behaving as a solid. The time that it takes concrete to change from a viscous liquid to a solid is not a constant, but depends on w/c ratio, specimen size, temperature, inclusion of admixtures and the type of test used. The use of HRWRA retards the temperature increase caused by heat of hydration as well as the initial strength and stiffness development, but this trend is reversed within 24 hours of casting. A comparison between the setting times calculated from load application (such as penetration testing) and other setting time methods (such as derivatives of heat of hydration measurements) show that HRWRA have an influence on the setting times. The mixes without admixtures gave similar setting times, when the average for the different tests were used whether calculated from load test data or from other setting time test methods. The use of HRWRA resulted in differences of almost 2 hours for w/c ratios below 0.45 between the different types of setting time measurements. This confirms that when load tests are used in mixes containing admix-tures, the time when concrete change from a Bingham fluid to a solid can be wrongly estimated. This incorrect assumption of setting time could cause an over estimation of the early age shrink-age that can cause stresses or cracking in high strength concrete.
Thermal effects on concrete properties
(University of Pretoria, 2024-02-12) Kearsley, Elsabe; megan.brink@up.ac.za; Brink, Megan
The expansion of nuclear energy as a future power source in South Africa, and the use of concrete for the containment vessels, has substantially increased the need for research in the concrete field. The production and development of environmentally friendly construction materials raise concerns about structural fire safety and thermal behaviour, as nuclear radiation shields face high levels of external heat and there is limited research on the performance of these materials at high temperatures. Therefore, the effect of elevated temperatures on the properties of concrete containing recycled aggregates, admixtures as well as blended cements is of importance in the design of concrete structures, such as concrete radiation shields. Operating temperatures of nuclear power plants range between 285°C – 650°C, depending on the reactor type. Other application such as outer shells of industrial chimneys or stacks and structures in metallurgy and chemical industry workshops, can also benefit from research on the thermal behaviour of concrete at high temperatures. This study highlights the notable influence of aggregate type on the performance of concrete subjected to elevated temperatures. It is well known that heating concrete to elevated temperatures causes shrinkage of the hardened cement paste as well as thermal expansion of the aggregates. This can cause microcracking within the concrete, leading to degradation of the Interface Transition Zone (ITZ) between the aggregate and hardened cement paste, resulting in a reduction in the concrete strength and stiffness. The study proofed that concrete exposed to elevated temperatures in service should preferably contain aggregate with a low coefficient of thermal expansion. Concrete exposed to 350°C retained more than 64% of its original strength, while concrete exposed to 500°C can retain more than 70% of its original strength after recovery as a result of rehydration when exposed to water. The order of preference of natural aggregate type for concrete exposed to elevated temperatures (up to 500°C) is felspathic (andesite, dolerite), granitic (granite, felsite) and calcareous (dolomite). Furthermore, high paste volumes (> 400 l/m3) show noticeably more deterioration in strength after exposure to elevated temperatures. It is therefore recommended that the use of concrete mixtures with excessive paste volumes or cement contents should be avoided. The use of SCMs, such as fly ash, showed higher strength deterioration compared to pure Portland cement concrete. This was attributed to the disruptive effects of the cement paste shrinkage opposed by aggregate expansion for concrete with a compact microstructure. RAC can compete with concrete made with aggregates from conventional quarries, not only under normal temperature conditions but also after exposure to high temperatures. Structural concrete can easily be manufactured where 100% coarse aggregate and 30% fine aggregate is replaced with RCA. It was hypothesised that aggregate that contain elements and minerals that decompose at relatively low temperatures, would place less stress on the surrounding cement paste, thus reducing the damage caused to the ITZ by the thermal expansion of the aggregate. The study established that the mass loss of aggregate obtained from thermogravimetric analysis (TGA) might give an indication of the performance of concrete exposed to elevated temperatures, especially considering dry compressive strength as well as mass loss of the concrete. The results indicate that it would be possible to limit the extent of thermal damage to concrete by selecting aggregates with limited (at least 1%) but not excessive (less than 2%) mass loss at the exposure temperature. The study demonstrated that degradation of concrete due to temperature exposure is not only caused by the thermal expansion of the aggregates but also by the mass loss of aggregates. To limit the damage caused to concrete by exposure to elevated temperatures, there seems to be a balance required between the thermal expansion of the aggregate and the reduction in stress caused by the aggregate degradation as indicated by mass loss of the aggregate at the specific exposure temperature.
Soil-structure interaction of horizontally loaded piled-raft foundations
(University of Pretoria, 2024-02-12) Kearsley, Elsabe P.; henilouw@gmail.com; Louw, Hendrik
Wind turbine power generation has gained significant popularity over the past few decades as an option for cleaner energy production amidst growing climate change concerns. However, the design of a turbine’s foundation, capable of supporting tall structures subject to large horizontal forces and overturning moments, remains challenging. The current focus with many new wind farm constructions is on taller wind towers, allowing for the same generation capacity from fewer wind turbines. Complex dynamic wind loading, which is amplified for taller wind turbines, and intricate soil-structure interaction between the foundation and the supporting soil require consideration to obtain foundation solutions that are both economical and sustainable. Although raft foundations are preferred for supporting onshore wind turbines due to cost and ease of construction, many researchers have recently favoured the use of piled-raft foundations. Not only do these foundations adequately support wind turbines when these towers are constructed on less favourable soils, susceptible to large settlements or low bearing capacities, but they also provide a substantial and more economical solution for resisting the significant overturning moment acting on the foundation. Yet, the response of these support structures is not well understood, especially considering that vertical loading is no longer the driving force in determining the size of these foundations, with loads dominated by the dominant horizontal load and overturning moment from the wind. Thus, given the increase in the dependency on these renewable energy structures and their size, the need to investigate this is important, given the strict design criteria and allowances. In this thesis, a full-scale onshore wind turbine piled-raft foundation supporting a 117 m high wind turbine located on a newly constructed wind farm near Wesley in South Africa was instrumented and monitored for an extended period of time. The data presented includes those obtained during construction, turbine installation, and during turbine operation. In addition, finite element (FE) modelling was also conducted on piled-raft foundations under these unusual load combinations, considering soil-structure interaction and foundation rigidity. The full-scale testing showed that the foundation response was dominated by the dynamic horizontal load and overturning moment, compared to the vertical self-weight of the turbine, as expected, with the loads shared by both the raft and the piles. As the number of wind cycles increased, the results from the instrumented foundation socketed into bedrock indicated that a greater portion of the applied loads were distributed amongst the piles. Given the significant rigidity of the pile connecting raft, the response of the piles was dominated by the push-pull effect. Seasonal temperature changes also affect foundation response, which is usually neglected due to the foundations being buried. Additionally, from the FE modelling, apart from the soil-structure interaction concepts that were considered, the relative stiffness between the pile and the raft proved valuable towards analysing the rotational stiffness of the foundation for wind turbine application, also allowing for the potential axial forces in the trailing piles to be limited, given the large horizontal loads and the significant overturning moments. Based on the responses observed from the full-scale testing and the results from the relevant FE models, it is clear that the upper limit has been reached regarding our current approaches to designing these foundations. In addition to the regular checks for restricting foundation settlement, differential settlement, horizontal displacement and meeting the minimum rotational stiffness requirements of the foundation, larger wind turbine models have presented additional critical design checks that cannot be ignored. These include the potential cracking of the raft under loading and the development of significant tensile forces in the trailing piles, both of which must be limited. Especially for larger turbine models, considering a balanced soil-structure interaction approach was shown to be beneficial. However, as mentioned previously, consideration should still be given to the constructability of these foundations, as larger foundations might result in more significant thermal gradients within the concrete section.
Design strategies for priority infrastructure for minibus-taxis at signalised intersections
(University of Pretoria, 2023-11-30) Venter, Christoffel Jacobus; u17040249@tuks.co.za; Mwenda, John Paul
The paratransit industry in South Africa which mainly includes the minibus-taxis is growing at a fast pace. Thus, it has become the largest mobility supplier to the urban public. In Gauteng province, the economic hub of South Africa that includes Johannesburg, Tshwane and Ekurhuleni, minibus-taxis account for 46% of all peak-period passenger trips followed by private cars accounting for 44%, while buses and trains account for a combined total of 10% of peak-period. Unlike buses which have seen the provision of priority infrastructure at intersections in the form of bus rapid transit (BRT) with priority transit signals (PTS) to improve their efficiency, minibus-taxis currently do not enjoy the same benefits. However, any efforts of road authorities in South Africa to consider incorporating priority infrastructure for minibus-taxis would be constrained by the absence of literature suggesting the ideal choices and the design analytical procedures. This research study aims to develop and evaluate design strategies for priority infrastructure for minibus-taxis at signalised intersections. Priority infrastructure at intersections can be in form of roadway facility infrastructure such as queue-jumping lanes, shared traffic lane, exclusive lanes or can be implemented via signal control. These infrastructure types are designed to provide efficiency benefits to road users mainly public transport such as buses. The first objective of this study is to develop an approach for identifying the design strategies for priority infrastructure for minibus-taxis at signalised intersections. A qualitative data method utilising document analysis technique is used to develop a framework matrix table to show the relationship between the geometric elements and the design treatments of priority infrastructure. Two categories of minibus-taxis (MBT) design strategies are then formed: 1) design strategies that only require repurposing of the existing intersection, 2) the design strategies that require major geometric improvements. Secondly, an analytical approach is developed to evaluate the performance of two proposed design strategies using real world traffic data. To begin with, four isolated intersections in the city of Tshwane are evaluated for feasibility of the MBT design strategies. The framework matrix analysis developed earlier is utilised to select and evaluate the design strategies associated with the four intersections. In addition, the intersections are further assessed for safety, traffic operations and cost effectiveness. Eventually, the two most effective design strategies are selected for a detailed performance evaluation: 1) a shared MBT lane to be used by through movement minibus-taxis and left-turning vehicles (MBT+LT) and 2) a dedicated MBT lane for through minibus-taxis only. The approach uses modified analytical principles from the Highway Capacity Manual (HCM) to measure the performance of the selected design strategies using peak hour traffic data. The performance measures include volume to capacity ratio (v/c ratio), average vehicle delay, and adequacy of storage length of MBT priority lanes. The performances of existing intersections are compared with the performances of intersections after implementing the MBT design strategies. In general, the results show that the two proposed MBT design strategies significantly improved the performance of minibus-taxis at intersections while slightly reducing the performance of traffic in non-priority lanes. Lastly, using the results from the two evaluated design strategies, a sensitivity analysis is performed on the modified HCM method to determine a range of traffic volumes for which the selected design strategies are feasible. Consequently, two models are set using a modified HCM method to evaluate two typical MBT design strategies involving a shared MBT lane and a dedicated MBT lane. The models are set to measure the v/c ratios of individual lanes on the approach as a measure of performances. The models are set to measure the highest v/c ratios while varying the traffic volumes at constant values of g/C ratios. The model outputs are in the form of graphs showing the relationship between left turning (LT) traffic, straight (MBT+T) traffic and v/c ratios at constant values of g/C ratios. These charts are developed as a planning and design guide when evaluating the feasibility of signalised intersections for the two evaluated MBT priority infrastructure types. Overall, the study provides the first detailed results supporting the viability of priority infrastructure for minibus-taxis at signalised intersections. It also gives a detailed methodology and steps that could be used by traffic engineers and planners to design and evaluate the performance of priority infrastructure for minibus-taxis at signalised intersections. The matrix framework method and graphs for traffic volumes could provide planners with a structured way to identify feasible designs for the priority infrastructure for minibus-taxis at signalised intersections. The methodology used in this study can be adopted to evaluate other types of design strategies not evaluated in this study. The study concludes that with well optimised design solutions, it is possible to use priority infrastructure to improve the performance of minibus-taxis at signalised intersections without adversely affecting the performance of traffic in the non-priority lanes
The development and implementation of an innovative smartphone application to collect route choice preference data
(University of Pretoria, 2023-07) Venter, C.J. (Christoffel Jacobus); u16401868@tuks.co.za; Hayes, Gary Patrick
The research presented in this thesis was motivated by two factors. Firstly, little route choice research has been undertaken in South Africa, especially in urban areas. This has resulted in significant gaps in our understanding of commuter route choice preferences and associated willingness-to-pay measures such as the value of travel time. Secondly, there are recognised limitations in the experimental methodologies used for route preference data collection, i.e., field data collected using revealed preference (RP) methods, and experimental data collected using stated preference (SP) methods. RP methods have high external validity, but the analyst has limited experimental control. SP methods have a high degree of analyst control of the experiment parameters, but the hypothetical nature of the route alternatives provides lower levels of external validity. The research presented in this thesis therefore had four objectives. Firstly, to provide a review of historical research and studies into mode choice and route choice modeling in South Africa and highlight any gaps in our understanding of commuter route choice preferences and the value of travel time. The findings confirmed that no route choice research has been undertaken in South African urban areas for the last two decades, and large gaps exist in our understanding of motorists’ route choice preferences these areas. The findings confirmed the urgent need to undertake route choice research in South African urban settings, especially in the light of the governments user pays policy for urban road and public transport provision. The second objective was to develop and demonstrate the proof-of-concept for an innovative, smartphone-based application with the acronym RAPP-UP (Route Choice Application – University of Pretoria), for collecting motorist route preference data in dense, congested urban road networks based on real-time traffic conditions at the time of the trip. The author of this thesis designed and prepared the specification for RAPP-UP, and an independent contractor was appointed to code the application and make it available on the Google Play Store® for survey participants to download. RAPP-UP was designed to achieve a better balance between external validity and analyst control. The third objective was to use RAPP-UP to collect route preference data from a sample of commuters in Gauteng Province, South Africa. The fourth objective was to estimate various types of discrete choice models to quantify different forms of route preference utility and estimate the associated willingness-to-pay measures such as the commuter value of travel time. RAPP-UP was designed for application in a self-validating survey context that included stated preference (SP) and revealed preference (RP) components. A degree of analyst control was introduced by allowing the analyst to factor the observed attribute levels before presentation to users in a predetermined manner based on an unlabelled fractional factorial design. RAPP-UP’s innovation was its ability to maximise external validity by generating two realistic alternative routes based on real-time road network travel data between a user specified origin and destination, thereby anchoring the experiment in a realistic and familiar setting. This innovation was enhanced by showing the route alternatives on a detailed road map background to provide orientation for the trip origin and destination locations, the routes themselves (highlighted on the road background), as well as the utility attribute levels for each route in a choice set format. After trading-off the attribute levels for each route, users were asked to choose their preferred route (SP component) and were then required to drive their chosen route (self-validating RP component). The GPS function in the smartphone was used to track the user to determine route adherence. An economic experiment was introduced by deducting the toll cost of a chosen tolled route from a user survey account that was allocated to each user at the commencement of the survey. The final survey account balance was paid to each user at the end of the survey. As each trip is one observation, the use of RAPP-UP was required over several days to obtain multiple observations from each user. RAPP-UP was designed to accommodate a detailed form of utility expression that contained a disaggregated form of travel time that specified the proportions of actual travel time (in minutes) in free-flow, slowed-down and stop-start travel conditions. The trip petrol cost (in Rands), toll cost (in Rands) and the probability of on-time arrival at the destination (in percent) were also included in the utility expression. To illustrate proof-of-concept, a small sample of car commuters in the Gauteng Province of South Africa was recruited to participate in a route choice survey using RAPP-UP. The road network in the urban areas of Gauteng Province is dense and congested in the weekday peak periods, and the motorways are tolled. The route preference data of the sample of commuters provided the basis for the estimation of various forms of discrete route choice models. The models confirmed that the attribute coefficients for each category of travel time were significant, thereby corroborating international evidence. The congestion multipliers, i.e., the ratios of the travel time attribute coefficients for each trip time category, were within the ranges determined in international studies. The petrol cost, toll cost and probability of on-time arrival attribute coefficients were also significant. A toll road quality bonus representing the unobserved factors of utility was introduced as a dummy utility attribute for routes with tolled sections. The attribute coefficient had a negative sign, revealing that the survey participants associated a disutility for routes with tolled sections for the unobserved factors of utility. All the objectives of the research were achieved. The research not only added to the body of literature on the topic of route choice behaviour in urban areas, but also provided insights into the practicalities of route choice data collection and model estimation.
The effect of environmental loading on restrained reinforced concrete T-Beams
(University of Pretoria, 2023) Kearsley, Elsabe P.; Skorpen, Sarah; ame.kleynhans@tuks.co.za; Kleynhans, Amé
Environmental conditions have the potential to cause stresses within reinforced concrete structures which equal or exceed the stresses caused by typical design dead or live loading. Concrete bridges are particularly susceptible to these effects as result of exposure to harsh environments throughout construction and service periods. The stresses caused by environmental loading are influenced by the material composition as well as the geometric properties of the structural element. Consequently, the selected type of cross-section used in bridge construction will influence the bridge’s response to environmental conditions. The main objective of this study was to compare the response of two scale model T-beams with different cross-sections to environmental loading, with specific focus on temperature and shrinkage effects independently and in combination. The T-beams were designed to be solid and voided to emulate the configurations of solid spine beam and box girder bridge cross sections, respectively. The scale size of the T-beams had two major advantages. One advantage was the practicality of constructing moulds and casting smaller sections compared to full scale sections. The second advantage was the ability to analyse the response of beams, commonly employed in construction and of similar size, to environmental loading. This expands the scope of considerations beyond bridge design applications. The stress profiles through the T-beams were of particular interest since they provided clear insights into the conditions which caused tensile stresses which exceeded the tensile capacity of the concrete and should therefore be considered within design. In order to calculate the stress profiles in both vertical and transverse directions, the temperatures and strains throughout the T-beams had to be recorded. Thermocouples and Vibrating Wire Strain Gauges were embedded into the concrete and measurements of temperature and strain were logged at 15min intervals, from the time of casting for the duration of the study. To allow accurate strain measurement, the T-beams were designed and cast in a manner which allowed unrestricted free movement as far as possible. This was achieved by minimising the constraints imposed by the supports. Typical daily thermal stresses were considered and factors such as heat of hydration and drying shrinkage over time were analysed to identify conditions which caused tensile stresses greater than the tensile strength of the concrete. This study showed that cross-section type and restraint conditions had significant effects on T beam behaviour in response to environmental conditions. The solid T-beam developed smaller longitudinal stresses caused by shrinkage and temperature but highlighted the need to consider the stress differentials in the transverse direction as well as the web to flange thickness ratio. The voided T-beam was more prone to curvature caused by temperature, shrinkage and swell, but developed more uniform stresses in the transverse direction of the section. Furthermore, the largest stress component was caused by the restraint of average longitudinal elongation and contraction of both T-beams, which emphasized the need to consider the timing at which restraint is applied to concrete elements.
Contribution of matric suctions to the slope stability of tailings dams
(University of Pretoria, 2023-06-01) Jacobsz, S.W.; Torres-Cruz, Luis Alberto; u17029016@tuks.co.za; Basson, Jack Adriaan
The strengthening effect of matric suctions is typically ignored in slope stability analyses. This is due to the uncertainty in the magnitude and reliability of in-situ matric suctions and the effect thereof on the shear strength of the material under consideration. Recent developments in field measurement probes allow for the long-term monitoring of in-situ matric suctions and volumetric water contents. The UP tensiometer was installed alongside volumetric water content sensors at various locations on a platinum and a gold tailings dam and monitored for a number of months. The inclusion of matric suctions in slope stability analyses required the identification of a suitable model from the literature that can realistically predict the relationship between suction and shear strength. Shear strength vs suction data were generated by shearing various platinum tailings samples using a direct simple shear device. Matric suction was varied between tests by varying the sample water content to observe the effect of suction on shear strength. Limit equilibrium slope stability analyses of the monitored tailings dams allowed the effect of matric suctions on slope stability to be considered once a suitable unsaturated shear strength model was identified that best modelled the shear strength test results. The effect of matric suctions on slope stability was illustrated by comparing safety factors determined using the classical approach, which only relies on saturated soil mechanics and the Mohr-Coulomb (MC) strength model, and an approach which replaced the MC strength model with a suitable unsaturated shear strength model. The results of unsaturated direct simple shear testing of platinum tailings showed that the model by Vanapalli et al. (1996) best predicts the relationship between matric suction and shear strength. This model, together with the observed unsaturated pore pressure regime observed in the tailings dams monitored, were used in limit equilibrium analyses to assess the contribution of suctions to the factor of safety against slope failure. It was found that the contribution of matric suction to the factor of safety against slope failure ranged between 1.6% and 3.8% for the platinum tailings dam and between 5.6% and 13% for the finer grained gold tailings dam considered in this study. It was thus concluded that the contribution of matric suction to the stability of the platinum and gold tailings dams investigated was small and that it would be both conservative and realistic to disregard.
Optimisation of microstructural properties and mechanical performance of asphalt mixtures
(University of Pretoria, 2021) Maina, J.W. (James); none; Busang, Selinah
Excellent gradation with good strength aggregate morphology and quality binder significantly affect the microstructural properties, which affects the mechanical performance of asphalt pavements. Selection of aggregate gradation with optimised complex geometric morphologies and contact point of interaction of aggregate particles to provide good interfacial interactions between aggregate and asphalt binder, which complies with specification requirements, is a lengthy trial and error procedure. Most successful mix designs were obtained based on the experience of the designer. This study’s first aim is to understand the influence of the chemical properties, texture, shape, strength, and, consequently, the microstructural properties and its resultant mechanical behaviour. The second aim is to optimise gradation and aggregate packing with idealised air voids without testing the microstructure in the laboratory. The materials selected in this study were three types of aggregate: granite 1(GD 1), granite 2 (GD 2) and limestone (GD 3), TK fibre and bitumen pen grade 40/60 and 70/80. MATLAB and Particle Flow Code (PFC3D) were used in this study to achieve and optimise the parameters that influence the stability of the aggregate skeleton, including highly detailed aggregate clumps, aggregates clump size range (gradation), and the packing density by using optimum air voids as an indicator. The virtual aggregate skeleton microstructure was built, and a triaxial test in the PFC3D was used. The anisotropic mechanical properties of the virtual aggregate skeleton, such as the normal contact force and void fabric, were measured using a scan line void method established along the angle 𝜃�� using fabric vectors and were obtainable using PFC3D. Additionally, the asphalt mixtures were prepared from three different aggregate sources to evaluate the influence of aggregates’ physical and chemical properties on microstructural properties. The microstructural properties were captured using a Charge-Coupled Device (CCD) digital camera and analysed using Image Process Analysis System (iPAS) software. The effect of the daily temperature variation of the environment on the corresponding temperature gradient through the depth of the asphalt mixtures layers was assessed. Tests including Marshall stability, wheel tracking, three-point bending beam and double tension-compression at two periods were conducted to investigate the relationship between the structural performance of the asphalt mixtures and their microstructural properties. Additionally, the normal contact fabric tensor (F) was developed to evaluate the interlocking of aggregate in asphalt mixtures, and a correlation with the mechanical performance was performed. Also, all the bitumen grades were modified with various percentages of Teak (TK) fibre contents to evaluate rheological properties through rutting, penetration, thermal conductivity, and multiple stress creep recovery tests. Base and teak modified binders were soaked in the sodium carbonate (NaCO3) salt solutions for different conditioning times to simulate rheological performance in semi-arid areas. The Kruskal-Wallis test, a non-parametric test, was used to statistically study the effect of stress level, and TK addition and the mean wise comparisons at a 95% confidence level were determined. Grey relational analysis was selected to evaluate the asphalt mixture's performance through chemical characteristics, strength, shape, microstructural properties, and modified binder. Parameters that influence the microstructure stability, such as aggregate size fraction range, shape percentage, Dominant Aggregate Size Range (DASR), aggregate densities, and Destructive Factor (DF), were optimised for all gradations using PFC3D. The results suggest a linear correlation between the evolution of normal contact fabric and void fabric. A scan line approach successfully identified and quantified the wall and loosening effects by quantifying the voids’ shape and orientation. The results showed that aggregate’ chemical oxides such as sodium oxide (Na2O) + potassium oxide (K2O) + calcium oxide (CaO) + silicon (SiO2) have a major effect on the electrical conductivity of granite samples at high temperatures and pressure. The results indicated that the higher amount of sodium oxide (Na2O) + potassium oxide (K2O) + calcium oxide (CaO) + silicon (SiO2) in the aggregate, the better the aggregate texture and the higher the number of contact points. In addition, high numbers of contact points have a notable impact on the Marshall stability, rutting resistance, dynamic stability, stiffness modulus and complex Poisson’s ratio at high and low temperatures. A good linear correlation between F and Marshall stability, dynamic stability and stiffness modulus was demonstrated. TK fibre modified bitumen provided greater rutting resistance, lower penetration, and lower thermal conductivity than the base bitumen binders. Compared to base bitumen, TK modified bitumen demonstrated reduced shear strain, higher recovery, and higher non-recoverable creep compliance. The TK fibre-modified bitumen binders had better resistance to the action of salt than the base bitumen. However, increased shear strain, reduced recovery, and increased non-recoverable creep compliance were observed for samples soaked in increasing salt concentration. The base bitumen and TK modified bitumen showed excessive softening and negative recovery at stress levels from 0.5k Pa due to increased soaking duration and salt content. The fabric tensor presented in this study is another approach that can evaluate the packing of aggregate in asphalt mixtures. The study concluded that aggregate contact properties directly influence the Marshall, rutting, and bending stiffness modulus for both low- and high-temperature performance of asphalt mixtures. The results for F and the number of aggregate contact points were similar. Therefore, F can also be used to evaluate the internal structural index. This investigation established that adding TK fibre to bitumen enhanced its toughness, which could improve asphalt fatigue performance, with the optimum level of TK fibres being 2% by mass of bitumen.
Influence of integral bridge abutment stiffness on backfill pressure build-up caused by seasonal temperature changes
(University of Pretoria, 2023) Kearsley, Elsabe P.; Skorpen, Sarah; u16006209@tuks.co.za; Havemann, Garfield George
Although the construction of integral abutment bridges (IAB) is simplified as the members are all cast monolithically with each other, the soil-structure interaction between the abutments and the retained soil significantly complicates their design. More complex thermal movement must be taken into account as opposed to the simplified methods recommended by existing design codes for jointed structures. The thermal expansion and contraction of the integral bridge’s deck forces the abutment into and away from the retained soil which causes changes to the earth pressure distribution along the height of the abutment over time. For longer integral bridges, these changes are more pronounced and have greater influence on the design of the bridge. The density of the sand increases with time due to the cyclic loading caused by the thermal action of the IAB and therefore results in a stiffer backfill against the abutments. The earth pressure build-up will occur for each thermal cycle and is highly dependent on the nature and properties of the soil and the structural stiffness of the deck and abutments of the integral bridge. This development in earth pressure over time due to cyclic loading is known as the strain hardening/soil ratcheting effect of soils and is more severe for longer bridges and for greater numbers of applied thermal cycles. Based on current literature, it is postulated that the retained soils can reach Rankine passive pressures during the bridge’s design life. Large settlements can also be expected at the face of the abutments due to the corresponding volume reduction caused by the beforementioned densification of the sand that is continuously taking place. It has been identified that sands generate the greatest rate of earth pressure development for the same amount of applied thermal cycles compared to finer soils such as silts and clays which have significantly more resilient behaviour and displayed significantly less increases in pressure over time. There is considerable uncertainty regarding the behaviour of the abutments of integral bridges due to cyclic temperature changes as the entire system (i.e., the bridge structure and retained soil) is highly dependent and influenced by each other. International design codes recommend length restrictions for the different types of integral bridges and are heavily governed by the amount of settlement at the abutment faces. The main objective of the study was to identify the effects of integral bridge abutment stiffness during soil ratcheting caused by temperature change. More specifically, seasonal temperature changes were investigated as the bridge deck is expected to expand the most during these cycles compared to daily cycles. The earth pressure evolution of a coarse silica sand, mechanical behaviour of the sand particles (displacements and particle flow), resiliency of the retained fill, and the overall structural behaviour (deflection, curvature, and bending moments) were evaluated experimentally by varying the stiffness of the substructure of several model integral abutment specimens that were constructed from reinforced concrete. Current literature has only investigated the soil-structure interaction of scaled abutments in the geotechnical centrifuge that were made from steel or aluminium. It should be noted that there does exist few studies that have incorporated larger scale models, and as such this study aimed to demonstrate more realistic IAB behaviour based on the constructed concrete specimens. After testing of multiple specimens (each having different relative stiffness to the bridge deck) it was found that the degree of restraint exerted by the retained sand after 120 seasonal cycles (recommended design life of integral bridges by the British Standards) increased for greater abutment stiffnesses. It was found that the shape and magnitude of the pressure distributions as well as the structural behaviour demonstrated significant dependence on the stiffnesses of the abutment and retained sand. Based on the experimental data, the optimum choice of stiffness for the abutment specimens was evaluated.
Controlling capillary pressure in concrete to prevent plastic shrinkage cracking
(University of Pretoria, 2022) Boshoff, William P; Smit, Martha S; stiaandeysel@gmail.com; Deysel, Renier Christiaan
Plastic shrinkage cracking occurs in concrete members with large exposed surface areas, such as concrete pavements, bridge decks and floor slabs. Current research has shown that a notable increase in plastic shrinkage was observed in the engineering practice, leading to considerably more cracking problems than in the past. Plastic shrinkage cracking occurs when the plastic shrinkage of fresh concrete is restrained, leading to tensile stresses, which result in cracks when the tensile strength is exceeded. Plastic shrinkage is caused by negative capillary pressure build-up in fresh concrete. Controlling the negative capillary pressure build-up makes it possible to reduce the risk of plastic shrinkage cracking. The aim of this study was to develop a model that uses live in-situ capillary pressure measurements in fresh concrete to control the capillary pressure build-up to prevent plastic shrinkage cracking at any evaporation rate. A model was developed that calculates a critical pressure limit for when an action is needed to prevent plastic shrinkage cracking. The model uses the negative capillary pressure build-up area between two crucial time points in plastic shrinkage to determine this limit. The proposed model was tested and verified in two phases. The testing and verification of the model were conducted on a low bleed concrete having a water/cement ratio of 0.5 and a self-compacting concrete with a water/cement ratio of 0.4. Tensiometers were used to measure the capillary pressure build-up in concrete. The first phase consisted of determining the parameters required for the model. The second phase used the determined parameters to test the model with the two concrete mixtures at various evaporation rates. The results showed that the model could determine a critical pressure limit relevant to the concrete and evaporation rate. The proposed model proved to be a valuable tool in controlling the capillary pressure and preventing plastic shrinkage cracking in low bleed and self-compacting concrete.
Development of appropriate synthetic design storms for small catchments in Gauteng, South Africa
(University of Pretoria, 2023) Loots, Ione; Smithers, Jeffrey Colin; jvs.mouton@gmail.com; Mouton, Jacobus van Staden
Urban stormwater drainage networks are frequently analysed in dynamic rainfall-runoff simulation models. These models use hypothetical rainstorm events (synthetic design storms) as input in the case of single event-based modelling. A significant number of methods to generate synthetic design storms are described in the literature. However, due to the abundance of methods some engineers are likely to base their method choice on familiarity with a method and preference. This could lead to the selection of an inappropriate synthetic design storm that will generate unrealistic peak discharge results. Therefore, the need to develop appropriate synthetic design storms applicable to single event-based modelling of small urban catchments in South Africa was identified. The aim of this study was to test the performance of the existing methods, and to identify the method, or methods, best suited for single event-based modelling of small urban catchments in the selected pilot study area. The completeness of the data was assessed, at-site design rainfall was determined, storm events were identified and analysed to obtain the general storm parameters, and synthetic design storms were generated and compared with the observed rainfall mass curves. The performance was evaluated based on the shape of the storm and the intensity, whereas the peak discharge and the runoff volume was evaluated using dynamic rainfall-runoff simulation models. The Mean Absolute Relative Error (MARE) was used as a measure to determine the Goodness-of-Fit (GOF) of the data. It was concluded that the Chicago Design Storm and SCS-SA curves are most suited for single event-based models. Improvements to the Chicago Design Storm and SCS-SA curves are proposed to better simulate design rainfall events and guidance is provided for further refinement.
Exploring the access/egress behaviour of rapid rail passengers through the application of nested logit models
(University of Pretoria, 2020) Venter, C.J. (Christoffel Jacobus); daniewatts@gmail.com; Watts, Daniel
The Gautrain is a rapid rail system in Gauteng, a province of South Africa. Currently, little is known about what causes the behaviour of Gautrain passengers concerning their choice of mode for their first- and last-mile trips. This thesis is a study of the first- and last-mile mode choice behaviour of Gautrain passengers. The study had three main aims. First, it aimed to develop the most accurate and statistically significant models of both first- and last-mile behaviour. Part of this aim was to try to understand the effect of non-traders on the stated preference data. To achieve this end, models were estimated with and without non-traders in the sample. Second, the study attempted to determine if there were any differences between commuters’ first- and last-mile behaviour. For this purpose, a stated preference survey was developed and put online. It was then marketed on the social media platforms of the Gautrain Management Agency, the body that manages the rail system. The results of the survey were analysed and cleaned of errors. Different discrete choice models were derived from the data to find the best fitting model structure. The last aim was to see how the developed models could be used to plan future access and egress services. Significant discrete choice models were developed on a reasonably representative sample of the Gautrain population. The best-fitting model structure was a nested one for both first- and last-mile trips. These models show that while first- and last-mile commuter behaviour was similar, there were some differences. In particular, people are much more sensitive to invehicle time for their last-mile journey in comparison to their first-mile journey. This exercise showed that although non-trader data reduced the effectiveness and significance of the model slightly, the data did not change the overall picture shown by the models without non-traders.
Railway condition monitoring using a hybrid multi-view stereopsis and real-time kinematic geolocation pipeline for dense reconstruction
(University of Pretoria, 2022) Grabe, P.J. (Hannes); u13025059@tuks.co.za; Broekman, André
Continuous, effective condition monitoring and measurement of railway infrastructure remains a cornerstone of effective maintenance practices. Nonetheless, the potential benefits associated with the rapid advancements in technology, and its adoption in the railway sector, are undeniable - and unavoidable. The aim of this research was to develop an autonomous, non-contact, optical measurement technique, termed Spooroog, that rivals the measurement performance of comparative, state of the art instrumentation with the objective of providing quantitative condition assessments of the track superstructure, namely the vertical mid chord offset measurements and classification of the rail profile. Spooroog is derived from the Afrikaans nouns “Spoor“ (rail) and “oog” (eye). The research methodology comprises a thorough review of existing literature and state of the art research developments, numerical estimations of camera geometry for robust structure-from-motion solutions, development of a low cost, cm accurate geolocation service, an end to end, dense point cloud reconstruction pipeline, development of the Spooroog prototype and accompanying post processing software implementation (Spoorpyp; “-pyp” (pipe)) and experimental work, followed by the analysis, interpretation and discussion of the results from which the conclusions and recommendations were composed. A hybrid reconstruction technique was developed, consisting of a traditional structure-from-motion pipeline for the sparse reconstruction of the 3 camera configuration, working in conjunction with a neural network-based, multi-view stereopsis model tasked with the dense reconstruction. MVSNet was trained on custom, domain specific, synthetic datasets embedding characteristic geometric and material features associated with the railway environment. The diffuse and specular material properties do not conform to traditional Lambertian constraints employed by traditional photogrammetric pipelines. A low-cost, cm accurate geolocation service was realised, providing the requisite geolocation priors necessitated by the poorly defined, linear camera sequence, ensuring convergence of the structure-from-motion pipeline. Spoorpyp in turn transforms the acquired datasets into accurate, high-fidelity, rectified, georeferenced dense reconstructions (point clouds) for geometry extractions. The viability and efficacy of exclusively training neural networks on synthetic datasets was successfully demonstrated with the deployment of a trained image classifier on a mobile smartphone, providing real time inference performance. Image segmentation required both sample averaging and genuine data samples to be effective. Combining both synthetic and genuine datasets for depth inference, proved the most effective. The performance evaluation of the real-time kinematic geolocation service illustrated comparative to commercial solutions, achieving a horizontal and vertical precision of 23 mm and 87 mm, respectively. Similarly, a horizontal and vertical accuracy of 4 mm and 15 mm, respectively, was achieved after surveying the antenna. The qualitative and quantitative performance of Spooroog was compared against six other established measurement techniques: aerial photogrammetry, a geometry measurement system (KRAB), light detection and ranging (LiDAR; Hovermap), digital levelling, visual simultaneous localisation and mapping (vSLAM) and real-time kinematic antenna surface mapping (RTK-ASM). An alternative track quality index to the established running roughness - the running range roughness - was developed for comparing the measurement techniques. The running range roughness accuracy of the vertical mid-chord offset measurements attained by Spooroog varied between 2.6 mm and 3.9 mm, outperforming state of the art LiDAR (6.00 mm), aerial photogrammetry (35 mm) and RTK-ASM (40 mm). Dedicated, instrumented track vehicles (TLV, 0.5 mm accuracy) and geometry measurement systems (KRAB, 0.5 mm precision) still outperform Spooroog’s accuracy by a significant margin. However, the georeferenced point cloud density of Spoorpyp’s reconstruction ranked second only to vSLAM - without the requirement of any surface preparations or scanning geometry limitations - with the benefits of cm accurate georeferencing, rectification and superimposed colour information. The results substantiate the versatility and dexterity of the Spooroog prototype as an alternative, supplementary measurement technique for accurately assessing the condition of the railway environment, without relying on mechanical contact with the rail profile.
Towards sustainable pavements : a reference document
(University of Pretoria, 2021) Maina, J.W. (James); shablaauw@gmail.com; Blaauw, Sheldon Alfred
A sustainable pavement has to be economically, socially and environmentally feasible at an acceptable level of risk over its design life. Practically, a sustainable pavement optimises a range of performance indicators including cost, functionality, safety, local economic and human development, emissions, climate change and resource use, amongst others, which is measured by using a suite of assessment methodologies. This thesis focusses on providing practical guidelines to characterise and evaluate the sustainability of a pavement. The objectives focus on a practical systems framework, populated with various methodologies and data sets, for the analysis of holistic pavement sustainability in South Africa. The overall scope of this thesis is the field of pavement sustainability focussing on environmental and social tenets. Sustainability contributes to the state of knowledge by defining pavement sustainability, developing a life cycle inventory, creating a social life cycle inventory, determining climate change assessment, doing a cumulative risk assessment, determining a sustainability index and providing an improved understanding of issues relevant to pavement sustainability. These methodologies include life cycle cost analyses, life cycle assessments, social life cycle assessments, performance evaluations and climate change assessments amongst others. Apart from a life cycle cost analysis few methodologies have sufficient-evidence-bases from which to draw confident results. The methodologies are rarely aligned to evaluate holistic sustainability. The fast pace of methodology development has also arguably left behind gaps in research. Most notably is the consideration of risks that may affect sustainability. Firstly, sustainability is an interrelated concept since the modification of one sustainable indicator affects the others. Secondly, changes to or addition of indicators, if not properly evaluated, may cause unanticipated and significant reduction in sustainability outcomes. It is essential to develop required evidence bases for these methodologies to enable holistic evaluations and provide for optimal pavement infrastructure provision in South Africa. Although this thesis provides an improved comprehension of holistic pavement sustainability, much still needs to be done to improve this understanding and merge the various concepts into a clear and concise framework. The recommendations in this thesis should be elaborated to ultimately aid in the sustainable development and management of South African pavement infrastructure.
The management of track-bridge interaction using monitoring based calibration
(University of Pretoria, 2021) Grabe, P.J. (Hannes); dylanjj1990@gmail.com; Jacobs, Dylan
Continuous welded rail (CWR) has become an attractive solution in modern railway track to improve safety and rider comfort as well as decrease maintenance. CWR on railway bridges also has several advantages, however, additional rail stress can be expected and it is, therefore, important that the track-bridge interaction phenomenon is understood. Considerable longitudinal rail forces and displacements may develop in CWR track on long-span bridges. Any movement of the bridge deck induces a movement of the CWR track and additional rail stress. To reduce longitudinal stress in the rail, the length of the bridge can be reduced to a maximum expansion length that does not result in excessive bridge deck displacements, by altering the static arrangement of the bridge to relocate the “thermal fixed point”. An alternative method to reduce longitudinal rail forces and displacements on long-span bridges is to install a rail expansion joint (REJ). However, this is not an attractive solution as these devices cause local disturbance of the vertical track stiffness and track geometry which requires intensive maintenance. The study first evaluates bridge temperature as an input parameter to the evaluation of the track-bridge interaction phenomenon. The results of the study confirm that the concept of an effective bridge temperature, supported by literature published by Emerson et al. (1976), is an effective means of defining the uniform bridge deck temperature and calculated effective bridge temperature results correlated well with bridge displacement measurements. Thereafter the study evaluates site data obtained to understand the mechanisms contributing to additional compressive stresses in the rail due to track-bridge interaction. This was compared to permissible levels of rail compressive stress which were taken from established codes of practice. The need for a rail expansion joint on the Majuba Rail Bridge was confirmed by numerical modelling and high compressive rail stresses resulting in lateral buckling can be expected in the absence of an REJ. The vast difference in recommended values in various literature, ranging from 30 m to 200 m, supports the need for further evaluation of track-bridge interaction due to total bridge expansion length. The numerical analysis also confirmed that alternatives to an REJ, such as ballasted track or Zero Longitudinal Restraints (ZLR’s) were ineffective on a bridge expansion length of 314 m. Finally, results from the numerical model demonstrate that additional compressive rail stress can be reduced to permissible values, as per UIC Code 774-3R (2001), by reducing the total bridge expansion length, by altering the static arrangement of the bridge, from 314 m to 120 m which compares well with results published by Esveld et al. (1995), Rhodes & Baxter (2016) and McManus et al. (2017). The site investigation was undertaken on the newly constructed 68 km Majuba Rail Corridor to measure various parameters that influence track-bridge interaction. The structure is a continuous concrete bridge girder spanning 314 m over the Vaal River approximately 37 km south of Ermelo. Analysis of the bridge displacement, rail displacement and rail creep data indicate that although the rail is fastened directly to the bridge deck by means of elastic fastenings, a relative displacement of up to 6.5 mm, occurred between the bridge deck and rail. This is understood to be as a result of rail creep and “breathing length” associated with thermal loading. Approximately 78% of the displacement at the REJ is due to the high fixity Slab Track rail being pulled by the bridge and the remaining 22% is due to the ballasted rail track on the embankment “breathing” towards the discontinuity at the REJ. Rail creep for the high fixity switch blade accounted for less than 2% of the total rail creep. Rail creep is, therefore, primarily a function of “breathing length” from the ballasted track on the embankment for this bridge and REJ configuration. Midas Civil 2021 was used for numerical modelling. Displacement and axial stress results from a calibrated model compared well with the site data and published stress profile diagrams.
Condition monitoring of train wheels using a cost-effective smart rail pad
(University of Pretoria, 2022) Grabe, P.J. (Hannes); heinvschalkwyk@gmail.com; Van Schalkwyk, Marco Heinrich
The present study focuses on the condition monitoring of train wheels utilizing an 3D printed rail pad that is embedded with widely available accelerometers and a strain gauge. This smart rail pad was used on a heavy haul railway line to monitor train wheels by identifying any wheel defects and measuring the respective wheel loads. A series of laboratory material tests were conducted on various 3D printing materials to access the right material for the smart rail pad. Dynamic and static loading tests were carried out to determine whether the 3D printed rail pads can withstand the typical forces exerted by a passing train. Field tests were done to determine the performance of the smart rail pads in operational conditions. Results indicated that the smart rail pads were able to identify 60 % of the wheel flats and able to measure the wheel loads by comparing it to the control measurements. Nonetheless, the smart rail pads presented a good correlation between the measured wheel loads and the true values, while the identification of wheel flats was influenced by the low sampling rate of the system.
Terrain profile roughness measurement and characterization
(University of Pretoria, 1988) Zaayman, Oswald Cornelius Dannhauser
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Development of a Pico conduit-hydropower turbin within a city's water distribution system
(University of Pretoria, 2021) Van Dijk, Marco; adriaankurtz@gmail.com; Kurtz, Adriaan August
Energy is the lifeblood of worldwide economic and social development. In recent years, South Africa (SA) has experienced local energy shortages that have resulted in interruptions in the supply of electricity, referred to as “load shedding”. During such times, the monitoring and operation of water infrastructure become problematic. In combination with a culture of vandalism and theft of infrastructure components that have resale value, infrastructure becomes inoperable at an ever-increasing rate. Equipment functionality and levels of bulk water service delivery could be maintained through the development of alternative energy-generation methods in all spheres of the South African national, provincial, and local government. Because of the energy shortages in SA, localised alternative energy-generation methods are being adopted to maintain the management and control of water systems. The solutions involve utilising energy more efficiently, optimising existing systems, and seeking new approaches for supplying electricity to water supply infrastructure. The introduction of small hydroelectric turbines and generators at strategic places where there excess pressure exists in the water supply and distribution system, is a relatively simple energy solution to recapture some of this renewable energy. This could typically be done at existing pressure-reducing stations (PRS) or anywhere along the pipeline, by extracting hydroelectric energy to meet a specific demand, without compromising the main functioning of the supply system. A number of water authorities throughout the world have realised the potential of conduit hydropower and have implemented generating schemes. In SA, there are 257 municipalities and several water supply utilities. All of these municipalities own water supply distribution systems that could be considered for hydropower installations. Fortunately, a number of conduit hydropower opportunities exist within City of Tshwane (CoT), due to its geographic location relative to the country's main water sources. In CoT, water is distributed through a large water system that comprises 165 reservoirs, 39 water towers, 10 863 km of pipes, and more than 280 PRSs – some of which are operating at pressures of up to 250 m. The current reality is that regular load shedding results in a loss of control over parts of the water supply network. Retrofitting a hydroelectric turbine in an existing system, is a solution to address the constant demand for electricity at specific locations. This will ensure that communication with reservoirs – not only in isolated areas – for various operational, maintenance, and infrastructure management reasons, is maintained. This includes telemetry, pressure management, flow control and 24-hour monitoring and security systems. In this study, a pico conduit hydropower turbine was developed and the application and the installation of a retrofit conduit hydropower unit into a city’s water distribution system was explored. The entire retrofitting process is described, with examples of three of the four types of conduit hydropower developments in CoT. A novel conceptual hydroelectric turbine generator was designed to be retrofitted easily in an existing valve chamber. The prototypes tested in this study resulted in the development of a pico hydropower unit (PHU) at a competitive cost. These PHUs could be applied in water lines, installed in series (inline) with the main water lines. An inline pressure wheel (IPW) was developed and tested extensively over a period of four months to a point where the first commercial PHU (IPW2) was ordered for installation in CoT at the Klipgat Hospital Reservoir. This unit generates adequate electricity from the water network before discharging into the reservoir. A simplified control system manages the generated power to store sufficient power to run the equipment on-site and shuts down automatically when not needed, to prolong system life. The operation of this commercial IPW will be monitored and data will be collected during operation to evaluate the unit’s performance and to contribute to future studies. The results could be used to improve the design and effectively of the commercial IPW series.

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