This paper briefly discusses various factors that need to be considered in setting maximum allowable risk levels for a project. These include the public's perception of risk, the benefits derfved from the project, the cost of reducing the risk and comparable levels of risk in related industries or similar projects.
When discussing risk in engineering there is, by implication, a chance of failure. If there was no chance of failure, there would be no risk involved. Failure can take place in a physical sense and in a civil engineering context this is normally spectacular or cataclismlc. Alternatively, failure can be the non-achievement of the original objectives or the desired end state. The risk associated with transportation engineering falls into the latter category and failure can result in substantial ongoing, indirect costs to the community, out of all proportion to the original transportation engineering deliberations.
The damaging effects of recent floods on bridges in South Africa has resulted in a reassessment of design procedures. The statistical and deterministic methods of flood peak determination appear to be Inadequate. Recent research by hydrologists indicates that an empirical approach may be more reliable. Furthermore, sensitivity studies of the resistance of bridge structures to peak floods with very low probabilities at exceedance may be preferable to applying a load factor to the effects of maximum floods with a return period equal to the usefull life of the bridge. Reliability theory and risk analysis, although difficult to any in practice, can give useful insights into methods of optimizing the design and reducing the sensitivity of bridge structure to the effects of the exceedance of design floods.
The paper discusses the initial stages and development of a method of riskbased dam safety evaluation for the Department of Water Affairs. Theanalysis methodology used by the Department is discussed briefly. The methods of calculation used to determine probabilities of failure and the way in which dambreak analyses are done are summarized. Guidelines that should be used by the decision-maker as regards factors such as the acceptability or otherwise of levels of threat and risk of dams are examined next, followed by a few conclusions and recommendations.
Recent events have initiated this review of current urban stormwater management practices, with the aim of stimulating debate. Owing to population pressures the urban environment contains special problems for the hydrologist. The administrative authority has to contend with several, often conflicting, demands on land use. Risk evaluation is generally done in a quantitative fashion only. Probability-related hydrological data is used to obtain a flood peak, which in the case of watercourses is used to calculate a flood level. In township areas above this level flood peaks are used to design a reticulation system, while in those below the specific flood level development restrictions are imposed. The paper questions certain aspects of this procedure, emphasizing the need for a qualitative assessment.
The paper draws attention to the fact that apart from the risks on construction contracts that arise from natural causes and changed requirements, both parties are exposed to risks that arise from unclear documentation, poor understanding of the documents and a lack of communication. These risks in relation to documentation arise from differing interpretations and misunderstandings that lead to conflict: once conflict has arisen the parties are exposed to the risk of extra payment or losses. The paper attempts to highlight some of the particular clauses and aspects of the documentation that can give rise to conflict and suggests some measures by which the exposure to such risks may be reduced.
Risk in the context of civil engineering construction is first discussed in broad terms, from an ideal or theoretical point of view, including the risk of loss of me and financial loss. The elements associated with risk are then identified, namely uncertainties in structural loading, member resistance and human error. Quantification of the risk of failure is then addressed. In a discussion of the notional risk implicit in overseas codes of practice as well as that in the proposed formulation for SABS 0160. The influence of load factors, material factors and importance factors on the level of risk is then illustrated.