http://localhost/xmlui/handle/123456789/1278 Mon, 06 Apr 2026 20:22:34 GMT 2026-04-06T20:22:34Z http://localhost/xmlui/handle/123456789/6917 Contractor-Related Factors on Performance of Bridge Construction Projects in Kenya: Case Study of Kenya National Highways Authority Anyika, Joan Otike Bridge construction projects face more challenges in their implementation compared to road and building projects. This is due to their complexity and iterative nature of implementation. There is global evidence showing that bridge construction projects perform poorly in both developed and developing economies, and this is based on a myriad of factors such as client-related factors, environment-related factors, project design, and contractor-related factors. Out of these, contractor-related factors have been shown to have a great influence on the performance of construction projects, but less empirical evidence exists in terms of bridge construction projects. Therefore, this study examined the influence of contractor related factors (staff, site, financial, and managerial factors) on performance of bridge construction projects. The theory of construction management and the theory of constraints are the theoretical underpinnings for this research. Descriptive research design was implemented targeting 18 bridge construction projects implemented at KeNHA from 2012 to 2023. A total of 18 projects and 144 key informants represented the research population. Out of the 144 participants, 98 respondents were involved in the survey. In the total 18 projects, 144 respondents represented the population. The actual sample size based on the respondents was 98 consisting of clients (19), consultants (14), contractors (8), engineers (39), environment and social guards (2), project managers (4), stakeholders (7), subcontractors (2), technical advisors (3), and 1 inspector. A self-designed structured questionnaire was administered to the respondents. Descriptive, Pearson (r) correlation, and ordinal least squares regression analysis were performed. The findings indicated that contractor-related factors explained 19.7% of variation in performance of bridge construction projects and was statistically significant at the 95% confidence level. It emerged that staff and management factors had a positive effect on bridge construction projects’ performance while a negative effect of financial factors was confirmed. Additionally, site factors did not have any effect on performance of bridge construction projects. The study concluded that staff and management factors had a positive outcome on performance of bridge construction projects while financial factors had a negative outcome on performance of bridge construction projects. Site factors had no relationship with performance of bridge construction projects. It is recommended that bridge construction companies should adopt flexible working hours for contractors to enable them to work with minimal interruptions that are associated with bridge construction projects. Second, policymakers should create policies that guide contractors in provision of safe working environments for their staff. Third, it is recommended that contractors should be provided with training to develop their skills in decision-making during the implementation of bridge projects. Lastly, it is recommended that the national construction agencies have a category for bridge contractors. MSc in Construction Engineering Wed, 11 Mar 2026 00:00:00 GMT http://localhost/xmlui/handle/123456789/6917 2026-03-11T00:00:00Z http://localhost/xmlui/handle/123456789/6913 Influence of Processing Parameters and Post Heat Treatment on Mechanical Properties of AISI 1025 Fabricated by Laser Engineered Net Shaping Tum, Elphas Kibet A 3D coupled thermomechanical model was developed to investigate the evolution of residual stress in AISI 1025 fabricated by Laser Engineered Net Shaping (LENS). The model, validated experimentally with an error margin of 4.24%, demonstrated reliable predictive capability. Process parameters strongly influenced mechanical performance, with optimal settings (270 W laser power and 7.1 mm/s scan speed) achieving a hardness of 169.17 HV, a relative density of 99.78%, and minimal porosity (0.91%). Residual tensile stresses was reduced to 131.83 MPa, accompanied by a refined microstructure. Post-processing revealed contrasting effects: quenching improved hardness by 22% due to martensite formation, but induced high tensile stresses (425 ± 14 MPa), whereas annealing at 850°C reduced residual stress by over 90%, improving crack resistance while lowering hardness by 25%. These findings highlight annealing as an effective strategy for stress relief, making AISI 1025 well suited for tool and die applications, particularly in filament production for Fused Deposition Modeling (FDM). MSc in Mechatronic Engineering Mon, 09 Mar 2026 00:00:00 GMT http://localhost/xmlui/handle/123456789/6913 2026-03-09T00:00:00Z http://localhost/xmlui/handle/123456789/6863 Evaluation of Ball Mill Liner Wear Using Discrete Element Method Kimani, Hillary Wainaina Mainstream mining techniques in developing nations are hampered by high investment capital demand. As a result, many low-income nations with abundant mineral deposits are where small-scale mining is most prevalent. The utilization of locally made machinery is necessary due to limited funding sources. These machines, however, are frequently unreliable and ineffective, which has a detrimental effect on size reduction of mineral ores. Science must therefore increase the overall effectiveness and dependability of these machines. A ball mill is a device for grinding rocks and assisting in the liberation of minerals for additional processing in the mining industry. The machine is made up of components such as the power source, the supporting framework, the drum, and the liners. The drum, which has a cylindrical or polygonal profile, is the ball mill’s primary working component. The latter profile is highly favored for artisanal mining due to its ease of fabrication. Due to the high abrasiveness of the majority of ores used in ball mills, liners are employed to lessen drum wear. The replacement of the liners is expensive and time-consuming because of the excessive wear that causes grinding inefficiencies. To increase production and lower costs, it is crucial to determine how different drum profiles affect liner wear. In this study, the discrete element approach was used to compare the severity of liner wear on the two drum profiles. First, particle model calibration was carried out using a hollow cylinder experimental setup. The model was then validated using a rectangular container method. For the liner wear model, calibration involved a drum wear test with a sliced drum geometry. Validation of the wear model was subsequently performed using the same drum wear test method, but with a full-scale drum setup. In both cases, experimental results were compared with simulation outcomes during the calibration and validation of the two DEM models. Although the octagon, decagon, and dodecagon geometries were taken into consideration in this work, the hexagon geometry was used as a depiction of the polygon profile. Further, lifters were incorporated into the two profiles, and their impact on the wear volume was examined. It was established that wear in the cylindrical profile was primarily due to material slip over the liner surfaces. However, the polygon profile wear was caused by both material slip over the liners and concentrated compressive force at the vertices. The influence of material slip on wear was thought to be greater on all of the profiles than the effect of compressive force. Thus, the cylindrical profile’s roundness made it easier for material to slide across the liner surface, which increased the wear on its liners. Instead, the polygon profile sides prevented material slippage, which reduced wear on its liner surfaces. The result was a wear difference of 17.9% on average between the two profiles at all speeds, with the polygon profile wearing out the least. Fitting of lifters in the two profiles prevented particles from sliding, causing a reduction of wear in all the profiles. Nonetheless, the wear caused by compressive force in the polygon profile was left unresolved. Therefore, the cylindrical profile fitted with lifters experienced 32.2% less wear compared to the polygon profile fitted with lifters, at all rotation speeds. Results obtained from this work are able to scientifically inform on the drum profile with least amount of wear. Additionally, results obtained will guide the artisanal miners on the design features to consider when fabricating a ball mill. This will lead to reduction in maintenance cost and enhanced efficiency of the equipment Master of Science in Mechanical Engineering Wed, 03 Dec 2025 00:00:00 GMT http://localhost/xmlui/handle/123456789/6863 2025-12-03T00:00:00Z http://localhost/xmlui/handle/123456789/6829 The Influence of Road Dimensional Structures on User Attitudes: A Case of Urban Roads in Nairobi, Kenya Ondieki, Janet Kemuma The dimensional structure of urban roads, which encompasses both geometric and aesthetic dimensions, holds significance in determining road efficiency, safety, and user experience. However, despite the existence of frameworks acknowledging the importance of road aesthetics in road planning, there is no clear criterion for assessing road aesthetics. This study aimed to analyse user evaluative responses by assessing urban roads in Nairobi, with a focus on their dimensional structure and user attitudes operationalised as likability. It was hypothesised that there are underlying latent structures linked to aesthetics within Nairobi's urban roads that influence road likability. A mixed-methods strategy was adopted for collecting, analysing, and interpreting quantitative and qualitative data. A systematic review of the literature was conducted to reveal empirical evidence of dimensions used as indicators of road aesthetics, which were further evaluated against Nairobi urban road scenes. Correlations among variables were established through content analysis, text mining and statistical procedures, namely factor analyses and linear regressions. The exploratory factor analysis conducted on the likability scores identified coherence, naturalness, and imageability as the intrinsic aesthetic characteristics of Nairobi roads. A comparison of the geometric design elements with the results of the cognitive assessment of the aesthetic dimensions revealed a correlation between variables, and maintenance as the paramount factor. The results also showed that road user type, gender, age, and frequency of road use affected the perception of the visual dimensions. These results suggest that the cognitive load differences among road users have an impact on the self-explanatory nature of roads, highlighting the need for careful participant selection during stakeholder engagement in road planning. The findings offer valuable insights into the dynamics of road planning. Objective measures for quantifying and evaluating road aesthetics were identified. However, this study does not establish a definitive threshold for achieving optimal road aesthetics or directly measure its impact on user behaviours. Consequently, it suggests the need for the simulation of road environments to capture real-time user reactions, to develop a model that accurately depicts the direct impact of aesthetic dimensions on road user behaviour. PhD in Urban Planning and Development Thu, 27 Nov 2025 00:00:00 GMT http://localhost/xmlui/handle/123456789/6829 2025-11-27T00:00:00Z