Assessment of existing structures under climate change

Assessment of the influence of human activities on recent, current, and future global and regional climate conditions and extremes has advanced sufficiently to provide a reasonable measure of its impact across the globe. The lack of concurrent adaptation of the design base for load bearing structures results mainly from the absence of a clear signal that climate change will have a significant effect on the climate actions that are accounted for in the structural design basis. The recent IPCC assessment of the physical science basis of climate change reports significant advances in observing and projecting changes in weather and climate extremes due to human influences. This provides an opportunity to reassess projections of future climate action conditions. Whilst the IPCC assessment confirms previous indications that, for example extreme wind will respond moderately globally, improvements in understanding and projecting changes show that trends will be overshadowed by uncertainties. The implication is that the design base will need to account for increasing uncertainties as climate actions are projected into the future, over the service life of existing structures, as well as those designed to current standards. The design base consequently in advance need to reflect continuous changes of existing structures

Resistance model uncertainty factors for ultimate limit state design of pile foundations

CITATION: Dithinde, M. & Retief, J. V. 2014. Resistance model uncertainty factors for ultimate limit state design of pile foundations. Journal of the South African Institution of Civil Engineering, 56(2):37-45.The original publication is available at http://www.scielo.org.zaENGLISH 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.AFRIKAANSE OPSOMMING: Geen opsomming beskikbaarhttp://www.scielo.org.za/scielo.php?script=sci_abstract&pid=S1021-20192014000200005&lng=en&nrm=iso&tlng=enPublisher's versio

Uncertainties in the South African wind load design formulation

CITATION: Botha, J., Retief, J. V. & Viljoen, C. 2018. Uncertainties in the South African wind load design formulation. Journal of the South African Institution of Civil Engineering, 60(3):16-29, doi:10.17159/2309-8775/2018/v60n3a2.The original publication is available at http://www.scielo.org.zaThis 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.http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000300002&lng=en&nrm=iso&tlng=enPublisher's versio

Variability of time independent wind load components

This paper investigates the variability of the primary time independent components of the design wind load formulation. It is shown that the variability of these components has a significant influence on the total reliability of wind loads. The use of comparative studies of international wind load standards as an indicator of the variability of the time independent wind load components is discussed. A two part comparative study is done to determine the variability. It is found that the existing representative probability model of wind load components underestimates even a lower limit estimate of the variability of these components, particularly for pressure coefficients. Furthermore, insight is gained into the effects of various structural and wind load parameters on the total variability of wind loads.Non UBCUnreviewedThis collection contains the proceedings of ICASP12, the 12th International Conference on Applications of Statistics and Probability in Civil Engineering held in Vancouver, Canada on July 12-15, 2015. Abstracts were peer-reviewed and authors of accepted abstracts were invited to submit full papers. Also full papers were peer reviewed. The editor for this collection is Professor Terje Haukaas, Department of Civil Engineering, UBC Vancouver.Facult

Review of climatic input data for wind load design in accordance with SANS 10160-3

CITATION: Goliger, A. M., Retief, J. V. & Kruger, A. C. 2017. Review of climatic input data for wind load design in accordance with SANS 10160-3. Journal of the South African Institution of Civil Engineering, 59(4):2-11, doi:10.17159/2309-8775/2017/v59n4a1.The original publication is available at http://www.scielo.org.zaENGLISH 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.http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192017000400001Publisher's versio

On standardization of the reliability basis of structural design

The principles of structural reliability are sufficiently advanced to be used extensively to develop design standards even at international level. The concept of limit states is generally accepted and implemented. Present standards are however to a large extent based on past experience, rather than on quantitative reliability modeling. It appears that reliability principles and models can bridge the gap between probabilistic assessment and operational design. Representative theoretical models are presented to indicate how judgment based reliability concepts can be complemented or replaced by the use of such models. The importance of reliability levels, reference period, design working life, specified characteristic values of basic variables and methods to derive their design values from reliability procedures are demonstrated. On this basis a standardized basis of structural design can be formulated to convert the reliability principles (such as provided by ISO 2394) into operational design procedures (such as used by EN 1990 and other standards). It is concluded that reliability principles and models could contribute further to international harmonization of structural design.Non UBCUnreviewedThis collection contains the proceedings of ICASP12, the 12th International Conference on Applications of Statistics and Probability in Civil Engineering held in Vancouver, Canada on July 12-15, 2015. Abstracts were peer-reviewed and authors of accepted abstracts were invited to submit full papers. Also full papers were peer reviewed. The editor for this collection is Professor Terje Haukaas, Department of Civil Engineering, UBC Vancouver.Facult