Effect of decision parameter efficiency on target reliability

Target reliability forms the basis of most modern design standards and is intended to represent an optimal balance of safety and risk of failure. Previous research noted discrepancies between target reliability obtained using generic and case-specific cost optimization for SLS cases. The source of the discrepancies was identified as the efficiency of the decision parameter at increasing reliability. This research extends the investigation to cases of ULS failures and found similar discrepancies. Generic cost optimization assumes a linear dependence between the decision parameter and the structural resistance. Where the dependence of resistance on the decision parameter is superlinear, the generic was found to under-predict target reliability by up to 15%. A factor is proposed to adjust generically-obtained ULS target reliability to be more appropriate to specific ULS cases. The factor accounts for the efficiency of the decision parameter, the case-specific cost of safety and parameter variation. The adjustment factor represents a first step towards mapping generic to case-specific target reliability in the ideal of promoting safer and more cost-effective structures

Structural reliability of existing rc beams strengthened with UHPFRC tensile layers

A methodology for reliability analysis of reinforced concrete (RC) beams strengthened with ultra high-performance fibre reinforced concrete (UHPFRC) tensile layers is presented. The proposed methodology includes stochastic stress-block analysis of a section, assuming a perfect bond between the RC beam and the UHPFRC layer. Annual reliability analysis of the RC beam before and after the strengthening operation is conducted. Deterioration induced by chloride corrosion is incorporated into the analysis via a chloride induced corrosion model based on Fick’s law of diffusion and described stochastically to account for the epistemic uncertainty in the time to corrosion initiation and rate of corrosion. A plot for determining the required thickness of the UHPFRC tensile layer to upgrade to the required reliability level is also given, considering the time from construction to when the strengthening operation is conducted. The proposed approach is easy to apply for routine practice

Evaluation of decisions to rehabilitate South African dams in terms of the ANCOLD ALARP criterion and SWTP for human safety

Eleven case studies of dam rehabilitation projects in South Africa are evaluated in terms of quantitative risk assessment criteria (ANCOLD, 2003) and Society’s Willingness to Pay (SWTP) (Pandey, et al., 2006). Inspection and design reports on which the decisions to rehabilitate were based were made available by the Department of Water and Sanitation, South Africa, from where estimates of pre- and posterior probabilities of failure, expected loss of human lives as well as cost of rehabilitation were obtained. In all cases, ANCOLD’s ALARP criterion dictated that the (existing) dams be rehabilitated. Only one of the eleven cases requires rehabilitation based on the SWTP criterion. The other cases either had a prohibitively high rehabilitation cost, an already low probability of failure prior to rehabilitation or low expected loss of lives in case of failure.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.FacultyOthe

Economic optimization considerations in South African dam rehabilitations

Economic optimization is applied to eleven case studies of actual dam rehabilitation projects in South Africa. The optimization includes the cost of rehabilitation and damage- and compensation costs for lives lost in case of dam failure. Economic motivation for the existence of the facility is excluded from the optimization. Five of the eleven cases would require rehabilitation based on economic optimization. The other cases either had a prohibitively high rehabilitation cost, an already low probability of failure prior to rehabilitation or low expected loss of lives in case of failure. Costs to improve safety for the different cases was typically between ZAR 0.5 and 5 million per percentage reduction in the probability of failure over a 50 year design life, but could be as high as R50m/%. A high cost per percentage reduction is typically associated with dams that already had a low probability of failure prior to rehabilitation. Interesting to note when the outcome is compared to other rehabilitation decision criteria is that ANCOLD’s ALARP criterion dictated that in all of the eleven cases the dams be rehabilitated, while only one of the eleven cases would require rehabilitation based on the Society’s Willingness to Pay utility function (Reynolds, 2013). Surprisingly, the cost of rehabilitation works is not considered as part of the South African Department of Water and Sanitation’s (DWS's) decision framework. Rational incorporation of this cost needs consideration.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

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

Traffic characteristics and bridge loading in South Africa

CITATION: Lenner, R., De Wet, D. P. G. & Viljoen, C. 2017. Traffic characteristics and bridge loading in South Africa. Journal of the South African Institution of Civil Engineering, 59(3):4–46, doi:10.17159/2309-8775/2017/v59n4a4.The original publication is available at http://www.scielo.org.zaENGLISH ABSTRACT: The loading model of the Technical Manual for Highways (TMH-7) published for bridge design in South Africa is in need of revision and simplification. The frequency of heavy vehicle loads has increased and the current application of the loading model is unnecessarily cumbersome. This paper aims to compare the heavy vehicle traffic loading of South Africa and Europe. A comparison of global internal bridge forces under the NA loading of TMH-7 and LM1 loading of Eurocode provides an indication of how current South African provision relates to the ones adopted in Europe. Above all, the traffic characteristics in South Africa are investigated in comparison to data used in development of LM1. LM1 loading generally results in higher internal forces when compared to TMH-7 loading. A direct adoption would thus imply more expensive bridges across South Africa without substantiation, considering the satisfactory past performance of existing structures. More importantly, the gross vehicle weights observed in South Africa are higher than those used for the development of LM1, indicating that the current TMH-7 distributed loading may be too low. Axle loads and their variability in South Africa are somewhat less than in Europe, so local design effects are less of a concern. It is apparent that further urgent work is required to establish a load model that reflects the current heavy vehicle traffic and predicts appropriate characteristic vertical loads.http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192017000400004Publisher'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