Assessing characteristic value selection methods for design with load and resistance factor design (LRFD) — design robustness perspective

An important step in load and resistance factor design (LRFD) is the selection of the characteristic values of uncertain soil parameters, which can be quite subjective despite the simplicity of LRFD. This paper assesses five statistical methods for the selection of characteristic values for design with LRFD, focusing on the design robustness. A framework based on the consideration of safety, cost, and design robustness is proposed for assessing these selection methods. This framework is illustrated with an example, the design of a drilled shaft in sand using LRFD, in which the best overall method for selecting the characteristic values is suggested. The implication of the outcome of this study is quite significant in geotechnical engineering practice, as it provides guidance on the selection of the characteristic values for design with LRFD.