Faculty of Engineering and the Built Environment (Research Outputs)
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Item Modelling spontaneous combustion liability of carbonaceous materials(Springer Open, 2018-06) Onifade, M.; Genc, B.This paper presents predictive models to determine spontaneous combustion liability of carbonaceous materials (coals and coal-shales) using statistical analysis. The intrinsic properties and spontaneous combustion liability index were determined by testing 14 coals and 14 coal-shales from Witbank coalfields, South Africa. The relationship between these intrinsic properties (obtained from proximate, ultimate and petrographic analysis) and spontaneous combustion liability indices (the Wits-Ehac Index and Wits-CT Index) were established. The influence of the intrinsic properties of coal-shales in relation to coal properties affecting spontaneous combustion has been established using a statistical method. The linear regression analysis indicates better linear relationships between some of the selected intrinsic properties and spontaneous combustion liability index and thus, identifies the major intrinsic factors affecting their liability toward spontaneous combustion. It was found that a definite positive or negative correlation coefficient exists between the intrinsic factors and spontaneous combustion liability. A set of models to predict the spontaneous combustion liability was derived. The best significant correlation along with the most appropriate model as indicated by R-squared values, the coefficient of correlations and standard error was used to predict the incident of spontaneous combustion.Item Optimizing Structures with Semi‑Rigid Connections Using the Principle of Virtual Work(Springer, 2018-04) Elvin, Alex; Strydom, JohnnieIn this paper, the virtual work optimization method (VWOM) has been generalised to consider structures with semi-rigid connections. The VWOM is an automated method that minimizes the mass of a structure with a given geometry, multiple deflection criteria, and load cases while adhering to design code requirements. In the optimization process, members are selected from a discrete database to meet all strength and stiffness criteria. Connections are modelled using rotational springs, allowing some moment transfer. The rotational stiffness of each connection can be varied from rigid to pinned. The example of a pitched roof frame is used to explain the method. Two case studies are considered: (i) (i) a three-storey two-bay and (ii) a four-storey three-bay office building. The VWOM produced results up to 26.7% lighter than results in the literature. Furthermore, the structures were optimized for a range of rotational stifness, where all connections in the structure were assumed to have the same rotational stiffness. Characteristic jumps in the optimized mass versus rotational stiffness were observed.Item Minimising the risk of thermally induced cracking in mass concrete structures through suitable materials selection and processing(Springer, 2018) Ballim, YunusThe hydration of cement is an exothermic reaction which generates around 300 kJ/kg of cement hydrated. In mass concrete structures such as dams and large foundations, this heat of hydration causes a significant rise in temperature in the internal sections of the concrete. If thermal gradients between the internal sections and the near-surface zone of the concrete element are sufficiently large, the thermal stress can cause cracking of the concrete. This cracking may cause functional or structural problems in the operation of the structure. In order to minimise the potential for such cracking, it is necessary to minimise the rate and amount of heat that is evolved, particularly during the early period of the hydration process. This can be achieved by design engineers and concrete technologists through judicious selection and processing of concrete-making materials. This paper presents the observations and results obtained over a number of years from adiabatic testing of concretes, computational modelling of temperature development in large concrete structures and direct temperature measurements in actual structures, with a view to understanding the effects of concrete-making materials on temperature development in concrete. The paper considers the effects of different types of rock aggregates, different types of Portland cement, fineness of grinding of the cement, the addition of supplementary cementitious materials and variations in the concrete starting temperature on temperature development in a large concrete element over time. The results indicate that using a coarser ground cement, adding significant amounts of supplementary cementitious materials and cooling the concrete mixture before placing has a more significant effect in reducing the risk of cracking than varying the aggregate type of the Portland cement type.Item Making A Mark: Wits School of Construction Economics and Management and Its Contribution to the Construction and Property Fields(University of the Witwatersrand, Johannesburg, 2025) Laryea, SamuelThis book is a historical account on the Wits School of Construction Economics and Management, its contributions and impact in society, which is very significant and leaves a positive impression of academic and industry development, despite historical hurdles. It looks at the past, present, and future of the School in the broader context of South African history and the overall development of the university. The process of writing this book has been both challenging and exciting with interesting discoveries about the academic disciplines and the growth trajectory of the School. It was challenging uncovering information from various sources within the university and external sources. It has also been an interesting process learning about the rich history and contributions of a key School within the university to the South African and global society. This book chronicles the careers of some graduates of the School who served in the highest leadership and management roles, and made an indelible mark in the construction industry locally and internationally. The School’s graduates have made substantial contributions to the growth and advancement of the South African construction and property sectors and their respective statutory councils including the South African Council for Quantity Surveying Profession (SACQSP), South African Council for Project and Construction Management Professions (SACPCMP) and the South African Council for the Property Valuers Profession (SACPVP). The School’s graduates have also played leading roles in major construction firms that have built some of the iconic buildings in South Africa and other parts of the world. In recent years, many of the School’s graduates are increasingly being recruited by firms in Europe, Middle East, Australia, and the US, indicating the quality of their education and their value to employers and the global construction industry.Item Making a Mark: Wits School of Construction Economics and Management and Its Contribution to the Construction and Property Fields(University of the Witwatersrand, Johannesburg, 2024) Laryea, Samuel; Smit-Stachowski, Alexandra; Mphuti, BongiThis book is a historical account on the Wits School of Construction Economics and Management, its contributions and impact in society, which is very significant and leaves a positive impression of academic and industry development, despite historical hurdles. It looks at the past, present, and future of the School in the broader context of South African history and the overall development of the university. The process of writing this book has been both challenging and exciting with interesting discoveries about the academic disciplines and the growth trajectory of the School. It was challenging uncovering information from various sources within the university and external sources. It has also been an interesting process learning about the rich history and contributions of a key School within the university to the South African and global society. This book chronicles the careers of some graduates of the School who served in the highest leadership and management roles, and made an indelible mark in the construction industry locally and internationally. The School’s graduates have made substantial contributions to the growth and advancement of the South African construction and property sectors and their respective statutory councils including the South African Council for Quantity Surveying Profession (SACQSP), South African Council for Project and Construction Management Professions (SACPCMP) and the South African Council for the Property Valuers Profession (SACPVP). The School’s graduates have also played leading roles in major construction firms that have built some of the iconic buildings in South Africa and other parts of the world. In recent years, many of the School’s graduates are increasingly being recruited by firms in Europe, Middle East, Australia, and the US, indicating the quality of their education and their value to employers and the global construction industry.Item Time and frequency nexus among public debt, exchange rate, inflation, monetary policy rate and economic growth in Ghana(Elsevier, 2025-01) Owusu Junior, Peterson; Odoom, Absalom; Adu-Asare Idun, Anthony; Akorsu, Patrick KwashieThe debate about the influence of public debt on an economy has gained long-standing attention among policy-makers, regulators and academic scholars. The excessive expansion of Ghana’s public debt to GDP demands a fresh insight into the macroeconomic variables that are connected to economic growth. This study utilised wavelet techniques to investigate the nexus and effect of public debt, exchange rate, inflation rate, and monetary policy rate on economic growth in Ghana using monthly data from 2000 to 2022. Diks and Panchenko (2006) was used as a battery test for the wavelet results. We found a significant negative correlation between public debt and GDP at both short- and long-term frequencies, though there was no notable connection in the medium term. The causality analysis suggests a possibility of bidirectional causality between GDP and public debt in both the short and medium term. Interestingly, the COVID-19 pandemic had minimal impact on this relationship when comparing the pre-pandemic and during-pandemic periods. The only observed coherence (negative) between monetary policy and GDP occurred between 2000 and 2003, at low and medium frequencies. The WMCC results depicted that no variable was seen to lead or lag during the pandemic period however, GDP (exchange rate) reacted to shocks first (last) in the short run (long run) prior to the pandemic. The result of this research is crucial for policy implementation. The GDP-public debt negative nexus offers strong evidence for the government to make determined efforts to reduce external borrowing. The positive coherence of exchange rates and the public debt offers a strong incentive to the monetary authorities to make determined efforts to stop the rapid rise of exchange rates.Item Balancing urban regeneration to prevent displacement: a conceptual strategy for inclusivity in South Africa(Proceedings of the AfRES 2024 Conference, 2024-09) Gethe, Faranani; Simbanegavi, PriscaThe regeneration of urban areas and neighbourhoods plays a crucial role in mitigating urban decay and enhancing socio-economic conditions. However, conventional urban renewal initiatives often inadvertently perpetuate geographies of exclusion, chiefly through gentrification and displacement. This paper is aimed at devising effective urban regeneration strategies that prioritise social inclusivity while mitigating the negative impacts of gentrification and displacement of poor people. The study employed a literature and theoretical review approach, utilising published articles and documents to assess the impact of urban regeneration programs on poor communities. The outcomes include the identification of shortcomings in current urban regeneration strategies and the need to formulate more equitable approaches. This study's significance lies in its contribution to expanding knowledge on urban redevelopment, particularly in the developing world of the global south. Furthermore, it will inform policy development aligned with Sustainable Development Goal 11 (Sustainable Cities and Communities) of the United Nations, thus facilitating much-needed advancements in urban development policies.Item Comparing occupant satisfaction in Green versus Conventional Residential Real Estate in South Africa(Proceedings of the AfRES 2024 Conference, 2024-09) Masotya, Adam; Simbanegavi, Prisca; Weaich, Malcolm; Adewunmi, Yewande; Ndlovu, Pride; Gethe, FarananiThis study compares occupant satisfaction in green versus conventional residential real estate in South Africa. It investigates the benefits and satisfaction levels related to green developments, particularly in terms of energy savings and socio-economic Impacts. The research aimed to determine if there is a significant difference in occupant satisfaction between green and conventional residential developments. A quantitative approach was employed, utilizing stratified random sampling to survey 160 occupants from two developments: Crossberry Central (green) and Little Manhattan (conventional). Data was analysed using the Mann-Whitney U and Wilcoxon W tests due to non- normal data distribution. The findings indicate that occupants of green developments report significantly higher satisfaction levels. Key areas of satisfaction include air quality, utility savings, and environmental benefits. Green developments demonstrate higher levels of satisfaction regarding reduced utility bills, improved indoor air quality, and contributions to environmental conservation. The study concludes that green residential developments significantly enhance occupant satisfaction compared to conventional housing. This suggests a socio-cultural shift towards valuing sustainable living environments, emphasising the importance of promoting green building practices to improve both environmental and occupant well-being.Item Phase proportions, carbon equivalent, mechanical properties and their effect on material cost of railway axle steels(Springer, 2018-04) Klenam, D.E.P.; Chown, L.H.; Papo, M.J.; Cornish, L.A.Commuter trains with solid axle configuration are produced from medium carbon steel due to cost restrictions. High-speed trains have hollow axle configuration for reduced weight and are made from high strength low-alloy (HSLA) steels. The HSLA steels have higher amounts of C, Cr, Ni, Mo, V and Nb, and are more expensive than medium carbon steels. The effects of phase proportions, carbon equivalent (CE), yield strength and ultimate tensile strength (UTS) on material costs of existing railway axle steels were studied using Thermo-Calc. Medium carbon rail axle steels had higher Fe3C phase proportions than the HSLA steel rail axle grades. Higher affinity of Cr, Mo and V for C than Fe resulted in decreased cementite proportions. The HSLA steels had yield strengths above 370 MPa, and UTS above 750 MPa, with increased material cost above $3300 per ton. A scattered distribution was observed for the pearlite weight fraction and material costs, with most between $3200 and $3400. The yield and tensile strengths increased with increasing carbon equivalent and pearlite weight fraction. The data aided the selection and design of alloys with better mechanical and corrosion properties at reduced material cost.Item In vitro Evaluation of Porous borosilicate, borophosphate and phosphate Bioactive Glasses Scaffolds fabricated using Foaming Agent for Bone Regeneration(Nature Research, 2018) Erasmus, E. P.; Sule, R.; Johnson, O. T.; Massera, J.; Sigalas, I.In this work, glasses within the borosilicate borophosphate and phosphate family were sintered into 3D porous scaffolds using 60 and 70 vol. % NH4(HCO3) as a foaming agent. All scaffolds produced remained amorphous; apart from one third of the glasses which crystallized. All produced scaffolds had porosity >50% and interconnected pores in the range of 250–570 μm; as evidenced by μCT. The in-vitro dissolution of the scaffolds in SBF and changes in compression were assessed as a function of immersion time. The pH of the solution containing the borosilicate scaffolds increased due to the typical noncongruent dissolution of this glass family. Borophosphate and phosphate scaffolds induced a decrease in pH upon dissolution attributed to the congruent dissolution of those materials and the large release of phosphate within the media. As prepared, scaffolds showed compressive strength of 1.29 ± 0.21, 1.56 ± 0.63, 3.63 ± 0.69 MPa for the borosilicate, borophosphate and phosphate samples sintered with 60 vol. % NH4 (HCO3), respectively. Evidence of hydroxyapatite precipitation on the borosilicate glass scaffolds was shown by SEM/EDS, XRD and ICP-OES analysis. The borophosphate scaffolds remained stable upon dissolution. The phosphate scaffolds were fully crystallized, leading to very large release of phosphate in the media.