Windhoek, Namibia
Windhoek, Namibia

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Cloete G.C.,Knight Piesold Consulting | Retief J.V.,Stellenbosch University | Viljoen C.,Stellenbosch University
Civil Engineering and Environmental Systems | Year: 2016

The rational quantitative optimal (RQO) approach presents a robust risk evaluation model which produces a definitive result for the reduction of risk from overtopping of earth-fill dams. The model is based on principles of risk, but an analysis of a portfolio of dams provides discrete optimal results, not expressed in terms of probability. All the steps that the methodology comprises have been developed exhaustively and propose to address concerns raised by dam owners and decision-makers regarding risk-based dam safety: a transparent framework for decision-making related to public safety, which will also appeal to the technically minded portfolio manager looking for a purely quantitative procedure to assist in the decision-making process. The RQO process is applied mechanistically, not requiring judgement from the decision-maker. In so doing it addresses the concern raised by dam owners regarding the judgmental probability of risk assessment. Risk in this paper is associated with embankment dams and external erosion, which is the single largest cause of failure of these dams. Also, in the context of this article, ‘optimal' refers to maximising lives saved over a portfolio of dams under the constraint of limited resources. © 2016 Taylor & Francis

Waye S.K.,Knight Piesold Consulting | Anderson A.,University of Texas at Austin | Corsi R.L.,University of Texas at Austin | Ezekoye O.A.,University of Texas at Austin
International Journal of Heat and Mass Transfer | Year: 2013

The increase in temperature of some consumer products, especially electronic devices, results in an increase of semivolatile organic compound (SVOC) emissions. Brominated Flame Retardants (BFRs), such as polybrominated diphenyl ethers (PBDEs), are used in many electronic casings and circuit boards to protect consumers from fires. However, the heat from the internal circuitry increases the SVOC vapor pressure and the material-air partition coefficient decreases, driving SVOC transport out of the substrate and into the indoor environment. In the case of a computer tower, the cooling fan also increases the mass transfer coefficient, further increasing emissions. Such enhanced emissions are a concern since recent studies claim adverse health effects of PBDEs on human health. In this study, a simplified heat and mass transfer model is developed to characterize the combined heat and mass transfer problem for a computer tower in an indoor space to determine the levels of PBDE that would be outgassed. As expected, higher temperatures increase the emission rate of the SVOC and explain one of the transport mechanisms for BFRs into the environment. The emission rate of PBDEs was on the order of tens of nanograms per hour. The concentration of PBDEs in the air increases 40-80% for every 5 C increase inside the computer case, depending on the congener. If these emission rates prove to be toxicologically significant, then models such as the one proposed can be used in risk analysis modeling and to develop mitigation strategies. © 2013 Elsevier Ltd. All rights reserved.

Tiznado A J.C.,Andrés Bello University | Paillao D.,Knight Piesold Consulting
Revista de la Construccion | Year: 2014

In the context of engineering practice, the problem of the seismic bearing capacity of shallow foundations has been solved indirectly, either due an increase of the static allowable soil pressures related to the probability of occurrence of the design earthquake or by adopting an equivalent pseudo-static approach. However, during last decades, a series of analytical methods that directly address the problem from the seismic point of view has been developed. This paper presents a parametric comparative analysis of different methods for estimating seismic bearing capacity of shallow strip foundations. Analytical methods, developed in the framework of both limit equilibrium and limit analysis theories, and also simplified design procedures typically used in practice were considered. The results obtained show an important decrease of the bearing foundation capacity with increasing of the maximum earthquake acceleration, which highlights the need to obtain a measure of the reliability associated with both calculation methods and safety factors commonly used for seismic design.

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