Browsing by Subject "Performance assessment"

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    Finite element model updating of concrete arch dams affected by alkali-silica reaction using ambient vibration monitoring and dam surveillance data
    (2025) Nyoni, Bukhosi; Moyo, Pilate
    Dams are important structures whose safety in operation is critical owing to the socioeconomic impacts associated with their collapse. Alkali-Silica Reaction (ASR) is a deleterious chemical reaction that affects the performance and safety of numerous concrete dam structures around the world. To ensure dam safety, a well-structured dam surveillance program that includes ambient vibration monitoring is essential as it enables an in-depth understanding of the behaviour of a dam in operation. Additionally, structural behaviour analysis through numerical models such as finite element (FE) models, is a crucial aspect of dam safety evaluations that allows dam safety engineers to predict the current and future behaviour of dams under various load combinations. The challenge in finite element analysis (FEA) is generating an FE model that is representative of the observed behaviour and condition of the dam to be trusted and used for further study. This study sort to find the best updating parameters and finite element model updating approach to achieve representative and reliable finite element models for the safety assessment of arch dams affected by ASR. This was achieved through sensitivity analysis of the behaviour (both dynamic behaviour and static behaviour) of concrete arch dams to (i) geometrical properties, (ii) material properties and (iii) load effects on the dam-foundation-reservoir system, to identify the best updating parameters. Following which a model updating procedure was proposed and implemented. It was observed that the behaviour of concrete arch dams is subject to their geometric properties. Their dynamic behaviour was observed to be largely sensitive to the dam- foundation-reservoir system stiffness and water level whereas their thermal behaviour was sensitive to the system thermal properties. Additionally, it was observed that the dynamic response is not as sensitive to ASR loading as initially assumed. Based on these findings, the proposed finite element model updating procedure begins with the updating of the system stiffness using modal parameters, followed by the updating of the thermal properties, and then updating of the parameters critical to ASR modelling. The proposed multi-step model updating procedure was successfully implemented to update a finite element model for a case study double curvature arch dam affected by ASR achieving agreeable results between the measured and predicted behaviour observations.
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    Open Access
    Performance management in times of change: experiences of implementing a performance assessment system in a district in South Africa
    (BioMed Central, 2018-09-14) Nxumalo, Nonhlanhla; Goudge, Jane; Gilson, Lucy; Eyles, John
    Background Health systems globally are under pressure to ensure value for money, and the people working within the system determine the extent and nature of health services provided. A performance assessment (PA); an important component of a performance management system (PMS) is deemed important at improving the performance of human resources for health. An effective PA motivates and improves staff engagement in their work. The aim of this paper is to describe the experiences of implementing a PA practice at a district in South Africa. It highlights factors that undermine the intention of the process and reflects on factors that can enable implementation to improve the staff performance for an effective and efficient district health service. Methods Data was collected through in-depth interviews, observations and reflective engagements with managers at a district in one of the Provinces in South Africa. The study examined the managers’ experiences of implementing the PA at the district level. Results Findings illuminate that a range of factors influence the implementation of the PA system. Most of it is attributed to context and organizational culture including management and leadership capacity. The dominance of autocratic approaches influence management and supervision of front-line managers. Management and leadership capacity is constrained by factors such as insufficient management skills due to lack of training. The established practice of recruiting from local communities facilitates patronage - compromising supervisor-subordinate relationships. In addition, organizational constraints and the constant policy changes and demands have compromised the implementation of the overall Performance Management and Development System (PMDS) – indirectly affecting the assessment component. Conclusion To strengthen district health services, there should be improvement of processes that enhance the performance of the health system. Implementation of the PA system relies on the extent of management skills at the local level. There is a need to develop managers who have the ability to manage in a transforming and complex environment. This means developing both hard skills such as planning, co-ordination and monitoring and soft skills where one is able to focus on relationships and communication, therefore allowing collaborative and shared management as opposed to authoritarian approaches.