Doctoral Degrees (Civil Engineering)

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Browsing Doctoral Degrees (Civil Engineering) by Author "Bakker, Frederik Pierre"

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    Characterisation of the South African extreme wind environment relevant to standardisation
    (Stellenbosch : Stellenbosch University, 2021-03) Bakker, Frederik Pierre; Viljoen, Celeste; De Koker, Nico; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: To ensure adequate structural resistance, engineers estimate the largest loads that windcan reasonably be expected to induce in a structure. In South Africa, operational designpractices are described in a set of standards, which include a wind loading standard (SANS10160-3) that provides guidance to engineers in estimating wind loads. The estimationprocedure described in the standard uses a basic wind speed, provided in a characteristicmap, that accounts for what the climate could produce at a particular location. This mapis based on inference from available wind speed observations using stochastic models.In an effort to improve the background information on which the standard is basedand in response to greater volumes of wind speed data, this dissertation presents a setof investigations which incorporate a greater quantity of relevant data, strive to improvethe stochastic model, and make specific recommendations that could be included in thenext revision of the South African wind load standard.A background study that summarises some of the most salient theory is also presented.This includes an overview of the South African extreme wind climate, extreme valuetheory, wind load standardisation, and reliability-based design.The quantity of available data collected by the South African Weather Service hasincreased substantially since the current standard was derived. This data had to bechecked for errors and classified by climatic mechanism. Following an attempt to correctfor the dynamic response of outdated instruments, the inclusion of historical data datingas far back as 1948 was also investigated. To be relevant for use in the standard, allthe data had to be measured according to World Meteorological Organisation standards.This was typically not the case, and so surface roughness correction was applied using aGeographical Information System technique. The expanded dataset includes data from an extensive network of 132 stations through-out South Africa, but the use of only annual maxima resulted in insufficient samplesizes at individual sites, potentially introducing substantial model-variance. In response,improved estimates by incorporating data from multiple sites within the region of studywere determined in this thesis. This included regional estimation of the shape of theprobability distribution, based on preconditioning the data by an exponent; and a separateinvestigation on optimal estimation of variability. For estimation of the variability, it wasshown that there was a balance between site and regional estimation, which was used todevelop an optimal estimator based on the bias variance trade-off.The expanded dataset and the insights into regional estimation were then applied toestimate design wind speeds that should satisfy the target reliability specified in the SouthAfrican standard. These estimates were incorporated into a new characteristic wind speedmap using a Monte Carlo simulation-based hypothesis test.