Doctoral Degrees (Civil Engineering)

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Browsing Doctoral Degrees (Civil Engineering) by Author "Bester, Andre"

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    Risiko-gebaseerde besluitondersteuning in siviele ingenieurswese: 'n metodologiese benadering tot verbeterende inligtingversameling en benutting
    (Stellenbosch : University of Stellenbosch, 2004-12) Bester, Andre; Retief, J. V.; University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT:Decisions affecting construction projects are often characterised by uncertainty. One of the sources of this uncertainty is the unit costs used in detail cost estimates. Analytical techniques are available to model these uncertainties, but information is required to quantify it. Historical data is the preferred source of information, but due to unavailability and unreliability it hampers the application of the analytical techniques. Changes in the construction environment necessitate the improvement of data sources and the utilisation thereof in a structured, comprehensive and integrated manner. The purpose of this study is to determine how decision-making can be improved by enhanced information capturing and usage of relevant data for improved cost calculations. This is achieved by investigating the various components of an information system, viz. dataflow, data source, data application, and shown how an integrated development of each of these components with processmodelling, database development and quantitative risk analysis can lead to improved decision-making. This is achieved by the conceptual redevelopment and development of information systems for decision support in two different construction environments, viz. road and dam construction, respectively. During the research it was found that processmodelling can contribute to the improvement of dataflow in the fragmented construction environment, but that shortcomings exist in the processmodelling tools. A method, based on set and graph theory, was developed to address it. It was also found that database development provides the opportunity to improve the quality of data stored in electronic format. A comprehensive database model to store all information relevant to construction costs, specifications and legal documents with the required error checking mechanisms was developed. The benefit of modelling the global uncertainty of project cost estimates with probabilistic techniques such as Monte Carlo simulation and the Limit State Cost Function, whilst including the effects of correlation, is also shown. The information gained from historical data-analysis, besides the application in the probabilistic techniques, was used to identify properties such as impact, variability and correlation. It was found in the study that a shortage of descriptive information, whether it be at project or item level, is predominately the source of variability in unit cost data after errors have been removed. In order to identify the information that would contribute to the lowering of variability a method was developed by using influence factors and unit cost correlation mechanisms to identify the most influential factors for data capturing. This led to the development of an ideal data-application model in which all the relevant data used in the different cost-estimation phases, viz. long term, conceptual and detail, would be captured and used. Based on what was found, a generic information system development model was proposed that indicated the interaction of all the aspects that were investigated. Two of the model’s foremost properties are its self-triggering process and incremental development (improvement). On top of this development model a development process was designed that can be used for the structured, comprehensive and integrated development/redevelopment of an information system for cost calculation.