Browsing by Author "Basson, Suzanne Esther"
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- ItemA conceptual index for benchmarking intermittent water supply in a water distribution system zone(Water Research Commission, 2020-01) Loubser, Carlo; Basson, Suzanne Esther; Jacobs, Heinz ErasmusVarious challenges, such as limited freshwater resources, climate change impacts, rapid population growth, urbanisation and underinvestment in water supply infrastructure, have led to intermittent water supply (IWS) in potable water distribution systems. Earlier research has confirmed that IWS negatively impacts the consumers, the infrastructure and the water supply authorities. Water supply authorities need tools to help understand IWS and the associated implications. A new indexing framework involving the causes and impacts associated with IWS is presented in this paper. In addition, a novel approach allows for quantification of the severity of IWS based on knowledge of a few readily available inputs. The severity quantification is based on two ratios: the intermittency ratio is a temporal measurement, accounting for supply duration; the connection ratio describes spatial aspects, using the number of service connections affected. The indexing framework and quantification tool could lead to improved understanding of IWS and could assist water supply authorities faced with IWS to make informed decisions. Improved planning of remedial actions to mitigate or avoid risks associated with IWS is aided. The tools presented in this paper could be used as basis for future development of a key performance indicator.
- ItemAn investigation into the reliability performance of bridges designed according to TMH-7(Stellenbosch : Stellenbosch University, 2020-04) Basson, Suzanne Esther; Lenner, Roman; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: South Africa’s bridge design code, called Technical Methods for Highways 7 (TMH-7), was last revised in 1988 and is partially based on an outdated code. Since then, the road freight industry has expanded significantly, further encouraged by changes to the traffic regulations. The expected reliability performance of TMH-7 in catering for the increased traffic demand is not clear. The purpose of this study is to investigate the structural performance of a new highway bridge designed according to TMH-7 and loaded with actual traffic loads. The study focus on the performance of TMH-7 for normal traffic conditions i.e. NA loading. A reliability analysis can provide a reliability index that measures the safety level of the structure. For the investigation, reliability analyses were performed for two case studies, based on actual traffic load effects derived from site-specific Weigh-in-Motion (WIM) data. The load effect is represented by the bending moment at midspan of a simply supported bridge. For both case studies the extreme traffic load effects were extracted and described in a probabilistic manner. By means of statistical projection the maximum load effect distribution for a 50-year reference period was obtained. The limit state function was then formulated to define the failure mode at the ultimate limit state (ULS). The First Order Reliability Method (FORM) was used to obtain an overall reliability index and the results were interpreted by comparing the reliability index to target values from existing standards. For the reliability analysis in the first case study, failure occurs when the actual traffic load effects exceed the design load effect for NA loading. Spans ranging from 5 to 50 metres were investigated. It was found that NA loading generally performs well for a typical highway bridge, especially for longer spans ranging from 30 to 50 metres. However, a poor reliability performance is seen for short narrow span bridges (especially for 5 m and 10 m spans), which agrees with previous studies. In the second case study, a critical element reliability analysis was conducted on a spine beam of a 20 m reinforced concrete twin spine deck. Failure occurs when the load effects exceed the resistance of the critical spine beam. High reliability indices were obtained, which indicate that NA loading is performing well for the bending moment capacity of a 20 m span bridge. Furthermore, a sensitivity analysis revealed that the traffic load and model uncertainty for resistance, have the most significant effect on the obtained reliability indices. With regard to bending moments at midspan, deficiencies in the traffic load model for NA loading were identified. Spans were also identified where design could be optimised to be more cost-effective. The study contributes to an improved understanding of the performance of TMH-7 for normal traffic conditions and can help direct future revisions of the traffic load model. It is recommended to extend the study to include other load effect types and to provide separate probabilistic descriptions for different loading event types.