Discussion of sensitivity factors and dominating variable for design value method

Abstract

The partial factor method is considered to be one of the most reliable design methods. However, engineers have examined the shortcomings of the partial factor method, primarily its flexibility and generality in searching for the values of partial factors. In order to improve upon the partial factor method, the design value method has been established on the basis of probability. The design value method is more flexible, general, and represents the developing direction of the reliability design method. However, based on experience, a set of sensitivity factors αi values has been developed. The sum of squares may be greater than 1.0 as a result of conservatism. Although some researchers have revised the values of αi by using the enumeration optimization method, the results are not ideal. This paper focuses on the recommended values of sensitivity factors that are applicable to the safety design as well as the serviceability design. It will be shown that these recommended values can improve the accuracy of the reliability index and present specific ranges of relative errors. This makes it possible to establish a practical design value method based on probability. In addition, a method to determine the dominating parameter is illustrated.