A straightforward moment method to estimate the load and resistance factors

Abstract

The load and resistance factor design is widely applied in engineering, where the load and resistance factors are introduced to account for the uncertainties in practice. Accurate estimation of the load and resistance factors is important for an appropriate design, which is generally conducted by the First Order Reliability Method (FORM). However, since the design point must be determined and derivative-based iterations have to be used, FORM is not practical for engineers. Furthermore, distributions of the load and resistance are required in FORM, which are usually unknown in practice. To overcome these deficiencies, moment methods are proposed, which estimate the load and resistance factors based on their moments. Although, the existing moment methods significantly reduce the iteration numbers, iterations are still necessary when higher accuracy is required. Therefore, a straightforward moment method is proposed in the present paper to estimate the load and resistance factors without iteration. The procedure of the proposed method is summarized in a flowchart with explicit expressions given. The accuracy of the proposed method is examined by comparison study among existing methods. It is shown that the proposed method is both accurate and efficient in estimating the load and resistance factors with no iteration required.