Doctoral Degrees (Civil Engineering)

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Browsing Doctoral Degrees (Civil Engineering) by browse.metadata.advisor "Day, P. W."

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    Reliability-Based Design in Geostructural Engineering
    (Stellenbosch : Stellenbosch University, 2018-12) De Koker, Nico; Viljoen, Celeste; Day, P. W.; Stellenbosch University. Faculty of Engineering. Faculty of Civil Engineering.
    ENGLISH ABSTRACT: Current standards used in South African geotechnical design practice follow the partial factor limit states design approach. Although partial factors used in this approach are calibrated for standardised target reliability levels, the approach does not take direct account of the probability of failure. Probabilistic reliability analysis provides additional insight to practitioners, making for potentially more optimal geotechnical structures. The technical committee responsible for drafting the South African geotechnical design standard has been requested by representatives of the geotechnical community to consider including standardised guidelines to reliability based geostructural design. As background research towards compiling the pre-normative report for such a set of guidelines, the use of reliability analysis in geostructural design needs to be considered in the context of the following problems. Firstly, the reliability analysis techniques appropriate to different geostructural design problems – a design standard can only be successful if the analysis methods are sufficiently accurate, robust, and practical to apply. Secondly, the appropriate statistical descriptions of the various model parameters – reliability analysis of civil structures is extrapolatory by nature, and so is very sensitive to the choice of functional form (distribution) and the values used to constrain its parameters. Thirdly, the minimum requirements on sample quality – sophisticated reliability analysis techniques have little value if parameter values are based on biased samples that are not representative of the material upon which the structure is to be founded. This thesis presents a number of studies associated with the issues listed above, from which it is concluded that geostructural design to a target reliability is possible, provided that the resistance model and the statistics describing its parameters are accurate and unbiased. However, it is shown that for this to be achieved, samples consisting of a greater number of specimens than currently used in routine geotechnical practice would be required, while the distribution types used to represent the various geotechnical material parameters should be standardised. Of the range of reliability analysis techniques available, the variants of the first order reliability method (FORM), in combination with an analytical surrogate performance function (response surface) where required, are shown to provide the best balance of transparency, economy, and accuracy.