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Reliability in Hydraulic Design
Abstract In hydraulic design, project reliability RE is defined as the probability that a project does not fail its purpose during its design life. It depends on the probability of failure PF, which is the probability of the project to fail in any one year. In cases of high resilience (such as a reservoir not meeting its target release), PF rather than RE is needed for design. In cases of low resilience (such as the dam of a reservoir failing through overtopping), the reliability is a more useful quantity because it incorporates the change of PF (or of the hazard function, which is a related quantity) with time. The present paper is concerned with the reliability-based design of hydraulic structures. In the first part of the paper, a general discussion of the concept of reliability-based design is given. It is shown that the probability of failure for a structure is not defined only through the hydrological input, but also depends on the parameters of the structure. The dependency can be expressed by means of generalized loads, and generalized resistances. In many cases of practical importance, loads and resistances are related by a joint probability distribution function (jpdf) and the failure probability can be obtained by elementary integrations. A discussion of PF and of the factors contributing to it illustrates that PF is an exact quantity for the ensemble of loads and resistances. For a sample of loads and/or resistances, or for other uncertainties, PF follows a probability distribution. The second part of the paper is concerned with the actual calculation of PF. This calculation involves an extrapolation of probability distribution functions (pdfs) of loads and/or resistances to extreme values, accomplished by means of extreme value analysis. A short survey is given of the most important pdfs suitable for empirical extreme value analysis. The results are illustrated by using an example of transformation of hydrologic data into hydraulic loads and calculating the reliability of the flood levee on a river which has been designed according to usual standards. It is shown that the actual reliability has very little to do with the exceedance probability of the design flood. A second example applies to the water quality of a river.
Reliability in Hydraulic Design
Abstract In hydraulic design, project reliability RE is defined as the probability that a project does not fail its purpose during its design life. It depends on the probability of failure PF, which is the probability of the project to fail in any one year. In cases of high resilience (such as a reservoir not meeting its target release), PF rather than RE is needed for design. In cases of low resilience (such as the dam of a reservoir failing through overtopping), the reliability is a more useful quantity because it incorporates the change of PF (or of the hazard function, which is a related quantity) with time. The present paper is concerned with the reliability-based design of hydraulic structures. In the first part of the paper, a general discussion of the concept of reliability-based design is given. It is shown that the probability of failure for a structure is not defined only through the hydrological input, but also depends on the parameters of the structure. The dependency can be expressed by means of generalized loads, and generalized resistances. In many cases of practical importance, loads and resistances are related by a joint probability distribution function (jpdf) and the failure probability can be obtained by elementary integrations. A discussion of PF and of the factors contributing to it illustrates that PF is an exact quantity for the ensemble of loads and resistances. For a sample of loads and/or resistances, or for other uncertainties, PF follows a probability distribution. The second part of the paper is concerned with the actual calculation of PF. This calculation involves an extrapolation of probability distribution functions (pdfs) of loads and/or resistances to extreme values, accomplished by means of extreme value analysis. A short survey is given of the most important pdfs suitable for empirical extreme value analysis. The results are illustrated by using an example of transformation of hydrologic data into hydraulic loads and calculating the reliability of the flood levee on a river which has been designed according to usual standards. It is shown that the actual reliability has very little to do with the exceedance probability of the design flood. A second example applies to the water quality of a river.
Reliability in Hydraulic Design
Plate, E. J. (author) / Duckstein, L. (author)
1987-01-01
34 pages
Article/Chapter (Book)
Electronic Resource
English
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