https://ir.unisa.ac.za/handle/10500/2924 2026-05-11T20:31:31Z 2026-05-11T20:31:31Z Morudu, Kagiso Ntate https://ir.unisa.ac.za/handle/10500/32261 2026-03-10T10:27:18Z 2025-09-01T00:00:00Z

Reliability analysis of studded shear connectors in composite slabs subjected to shear loading Morudu, Kagiso Ntate This study investigated the reliability of stud connectors in composite slabs subjected to shear loading, focusing on the adequacy and efficiency of design provisions outlined in four major international codes: SANS 10162-4, EN 1994, AISC 360, and AS/NZS 2327:2017. The analysis evaluated the safety margins and conservatism inherent in these codes, using both the First Order Reliability Method (FORM) and Monte Carlo Simulation (MCS) to assess the probability of failure of stud connectors under various loading and material conditions. The study began by analysing model uncertainty, revealing significant differences in bias and variability among the design codes. The SANS 10162-4 model showed no bias and minimal variability, while AISC 360 demonstrated the largest bias and variability. EN 1994 and AS/NZS 2327:2017 displayed moderate levels of conservatism. Reliability indices were computed for each design code, with results indicating that all models provided sufficient safety margins, though EN 1994 and AISC 360 exhibited excessive conservatism that may lead to overdesign. A sensitivity analysis based on FORM identified variable actions as the most critical factor affecting reliability, followed by stud diameter. The implications of these findings were used to propose adjustments to partial safety and reduction factors to optimize design efficiency without compromising safety. For instance, a reduction in the partial safety factor from 1.25 to 1.1 for EN 1994:2005, and an increase in the partial reduction factor for AISC 360 from 0.65 to 0.80, were recommended. The study concludes that while the current design standards provide adequate safety, there is significant potential for optimization, particularly in reducing conservatism in certain models. Future research is recommended to refine design models, account for more complex loading conditions, and explore probabilistic methods to further enhance the reliability and efficiency of stud connector designs. Limitations of the study include the use of simplified load conditions and assumptions about material properties, as well as the exclusion of long-term effects such as creep and shrinkage. In summary, this study evaluates the reliability performance of existing stud-connector design models and develops calibrated resistance factors that enhance their consistency with target reliability levels, providing evidence that can inform future improvements to design provisions while maintaining adequate safety margins.

2025-09-01T00:00:00Z Kgabile, Mpho Gift https://ir.unisa.ac.za/handle/10500/32122 2025-02-19T12:38:18Z 2022-12-21T00:00:00Z

Biodegradation of environmental significant inorganics using aerobic bacteria found in Blesbokspruit Wetland, South Africa Kgabile, Mpho Gift The Blesbokspruit wetland is known to be one of the imperative wetlands in Republic of South Africa (RSA), located in region of Ekurhuleni, Gauteng Province. A continuous discharge towards the Blesbokspruit wetland from effluents coming from the nearby Grootvlei mine, paper production company (South African Pulp and Paper Industries) and other anthropogenic activities accompanied with environmental impurities which include cyanide-residues has been witnessed within the wetland. Cyanide compounds depict distinct characteristics depending on chemical bindings with other elements which determines their severity and stability of the compound. Cyanides are either classified as either organic or inorganic cyanides and they are regarded as environmental significant contaminants. Biodegradation processes have proved to be an ideal tool to degrade environmental significant contaminants due to its cost effectiveness, eco-friendly and durability. The environmental significant inorganic placed under study is thiocyanate and its biodegradability using microorganisms isolated from soil, water and sludge within Blesbokspruit wetland. Among the most problematic inorganics found in wetlands are cyanides, particularly thiocyanate, which are toxicophores due to their cyanide content. Studies have shown that cyanides are present in effluents channelled by mining industries, which results in the deterioration of the Blesbokspruit wetland. Microorganisms were isolated and identified using universal primers 16S-27F and 16S-1492R, targeting 16S rDNA sequence. Indicator plate technique was applied in order to detect microorganisms with thiocyanate biodegradation capabilities, where phenol red aided as an indicator to distinguish microorganisms that can degrade thiocyanate by observing a colour change from red to pink. Later, thiocyanate degrading isolates and mixed culture were inoculated in minimal media without addition of a carbon or nitrogen source and 1/10th minimal medium containing a 24-hour starved culture was further inoculated in batch conical flasks containing minimal media with thiocyanate (SCN) either 150 mg SCN-/L or 250 mg SCN-/L. The sampling intervals were done every 24 hour-interval for a duration of 5 days, whereby the absorbance of microbial growth was measured at 600 nm and ammonium-nitrogen was measured with use of Merck Spectroquant Pharo 300. The results have shown that only few bacterial isolates were more effective compared to the bacterial consortium with regards to biodegrading thiocyanate, whereas the highest biological thiocyanate removal efficiency achieved in this study was 97.44 % and 95.71 % under 150 mg SCN-/L and 250 mg SCN-/L by Exiguobacterium sp., respectively. Most of bacterial isolates gave less biological thiocyanate removal efficiency as compared to bacterial consortium which was dominantly comprised by Pseudomonas sp. It was concluded that aerobic bacteria obtained at the Blesbokspruit wetland were capable of biodegrading thiocyanate which is deemed as an environmental significant inorganic. The greater concentration amounts of thiocyanate, most bacteria seemed to be susceptible to exposure, although few bacteria exhibited some form of resistance to some extent. Most of these bacteria were able nitrify the available ammonium-nitrogen.

2022-12-21T00:00:00Z Zong, Shuang https://ir.unisa.ac.za/handle/10500/31600 2024-10-15T12:51:28Z 2024-01-01T00:00:00Z

Controllable preparation and application of porous carbon-based electrode materials Zong, Shuang With the growing demand for energy storage and conversion technologies, porous carbon-based materials (PCMs) have garnered widespread attention due to their excellent electrical conductivity, high surface area (SSA), and good chemical and thermal stability. This study aims to develop PCMs and explore their applications in the field of energy storage and conversion. By carefully selecting carbon precursor and preparation process, I precisely controlled the pore characteristics and composition of PCMs, resulting in the fabrication of PCMs with different morphologies, including heteroatom-doped and porous carbon/transition metal composites. The morphology, structure, composition, and electrocatalytic performance of these PCMs were systematically analyzed. The specific research content and results are as follows: 1). This study focuses on the controlled preparation and electrochemical properties of one-dimensional porous carbon nanofibers (PCFs). Using a silica-assisted method, PCFs were synthesized and their electrocatalytic performance for supercapacitors (SC) were systematically evaluated. Optimal PCFs exhibits a hierarchical porous structure with high SSA (1407 m2 g-1) and suitable nitrogen doping. When used as electrode material for SC, it shows a specific capacitance of 314 F g-1 at 1 A g-1, excellent cycling stability (after 10,000 cycles at 5 A g-1), and 92.5 % capacity retention. In an assembled SC device, the energy density reached 31.9 W h kg-1 in 1M Na2SO4 electrolyte, and two PCF devices in series powered 2.2 V LEDs, demonstrating their practical potential. 2). The study also explores N/Co co-doped hollow porous carbon nanospheres (Co/N@PCS) as electrocatalysts for the alkaline oxygen reduction reaction (ORR), showing a half-wave potential of 0.81 V vs RHE and an onset potential of 0.91 V vs RHE, along with long-term durability in alkaline electrolytes. This work shows that the Co/N@PCS electrocatalyst has great potential in the field of alkaline ORR. 3). Wrinkled surface nitrogen-doped carbon nanotubes (NCTs) were prepared by a green, controllable template method. The optimal NCTs exhibits a high specific capacitance (336 F g-1) and excellent cycling stability (96.1 % capacitance retention after 10,000 cycles) in SC. 4). Additionally, nitrogen-doped porous carbon spheres (NPCS) synthesized by a simple self-template strategy with phenol formaldehyde resin oligomers (resol) serving as the carbon precursor and g-C3N4 as a self-template. The final NPCS possesses a high SSA of 880 m2 g-1, abundant pore structure and suitable nitrogen doping (2.35 %), exhibiting excellent performance as SC electrode material. 5). Porous Carbon nanosheets (PCNs) with adjustable thickness were synthesized by a template method and the electrocatalytic performance differences of PCNs with varying wall thickness were studied. The optimized PCNs, with a rich pore structure, large SSA, and moderate wall thickness, demonstrated a high specific capacitance of 278 F g-1,excellent rate capability (81.2 %), and good cycle stability (91.3 % capacitance retention after 10,000 cycles) as electrode material for SC.

2024-01-01T00:00:00Z Kassa, Ermias Abebe https://ir.unisa.ac.za/handle/10500/31484 2024-08-14T10:19:32Z 2023-01-01T00:00:00Z

Towards a human capabilities ontology in enterprise Architecture Kassa, Ermias Abebe This thesis aims at understanding and formalising human capabilities in enterprise architecture (EA). It begins by justifying why it is important for EA research and practice to consider human capabilities, and then proceeds to construct a computational ontology that defines human capability concepts and relationships in the EA domain. The research is motivated by the need to mainstream humans and their capability concerns into EA research and practice by creating mechanisms that would allow EA to function in an environment where the demand for equity, justice, sustainability, and progressive ideals is high. This research is in response to a call for more research from a holistic perspective of EA that takes into account shifting economic, environmental, and human conditions. Based on Amartya Sen’s human capabilities approach (HCA), which asserts that the true value of any developmental initiative lies in its potential and outcome to promote human capabilities, this research seeks to answer questions like what roles do or could human capabilities play in EA, what human capabilities should EA practices account for, and whether or not a human capabilities ontology can support EA practice. Within a design science research (DSR) approach, literature review, thematic analysis, framework synthesis, and ontology modelling are deployed to create the ontology artefact. A panel of experts from banking and finance, as well as higher education, were engaged to validate the ontology. The surveyed experts agreed that the ontology adequately reflects key human capability concepts and relationships pertinent to EA. They also acknowledged that the concepts are valid for a diverse user group. In addition to contributing to the paucity of literature at the interface of EA and human capabilities, this research promotes human capabilities-conscious EA practices. Both theoretical and practical applications of EA and the HCA stand to benefit from the ontology. By supporting a shared understanding of human capabilities in the EA domain, the ontology might enable enterprises and their stakeholders to develop a common vision for a sustainable future.

2023-01-01T00:00:00Z