Browsing by Author "Retief, Johan V."

Now showing 1 - 3 of 3
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    Resistance model uncertainty factors for ultimate limit state design of pile foundations
    (South African Institution of Civil Engineering, 2014-08) Dithinde, Mahongo; Retief, Johan V.
    ENGLISH ABSTRACT: The current limit state design procedure for pile foundations presented in geotechnical codes (e.g. SANS 10160-5, EN 1997-1) stipulates that, when the pile capacity is determined using an analytical approach, such as the static analysis using engineering properties of the soil as determined from laboratory or in-situ field testing, the prescribed partial resistance factors (γr) need to be corrected by a partial factor for the uncertainty in the resistance model (γR, d) or the resistance model uncertainty factor. The international position is to derive model uncertainty factors for both actions and resistances from available experimental data. Accordingly this paper makes use of a local pile load test database to derive the appropriate γR, d values for ultimate limit state design of pile foundations. The analysis indicates that γR, d values of 1.3 and 1.5 for piles in cohesive and non-cohesive materials respectively are appropriate. Alternatively, a single value of γR, d = 1.4 for all piles in all soils can be adopted with different γr values for the two distinctive pile classes of piles in cohesive and non-cohesive soils.
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    Review of climatic input data for wind load design in accordance with SANS 10160-3
    (South African Institution of Civil Engineering, 2017-12) Goliger, Adam M.; Retief, Johan V.; Kruger, Andries C.
    ENGLISH ABSTRACT: With the publication of Part 3 Wind Actions of the South African Loading Code SANS 10160:2010, several issues concerning adjustments from the reference standard Eurocode EN 1991-1-4:2004 could not be resolved due to lack of sufficient updated background information on South African conditions. The need for updating the map for the free field wind speed is related also to the improved representation of the mixed and complex strong wind climate of the country. Furthermore, strong wind probability models are used for the reliability assessment and calibration of wind design procedures. Updating of the reliability provisions for the revised wind loading process was a further need identified at the time. This paper provides a review of the historical development of the representation of the free field wind, used as input to design wind loading procedures for South Africa. The review considers: (i) the historical representations of the geographic distribution of free field wind, (ii) the climatic influences considered, and (iii) the probabilistic bases for the stipulated wind speed for the reliability provisions for design wind loads. On this basis, the background and motivation are provided for updating SANS 10160-3:2010.
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    Uncertainties in the South African wind load design formulation
    (South African Institution of Civil Engineering, 2018) Botha, Jacques; Retief, Johan V.; Viljoen, Celeste
    This paper presents an investigation of the uncertainties inherent in the South African formulation of design wind loads on structures, as stipulated by SANS 10160-3:2011. The investigation follows from the identification of anomalous values in the existing South African probabilistic wind load models during a reliability assessment of SANS 10160. The primary wind load components which have the greatest effect on the total wind load uncertainty are identified as the time variant free-field wind pressure, followed by the time invariant pressure coefficients and terrain roughness factors. A rational and transparent reliability framework for the quantification of the uncertainties inherent in the formulation of these components is then presented. Probabilistic models of these components were developed following independent investigations of each component. The results from these investigations show that the existing probabilistic wind load models underestimate the uncertainty of the wind load components, particularly when considering the time invariant components.