A new method for load and resistance factor design

Abstract

The reliability-based load and resistance factors design (LRFD) has been widely used in the structural design codes. In almost all of the current reliability methods for the determination of the load and resistance factors, the basic random variables are assumed to have known probability distributions The third-moment method has been proposed to overcome the shortcomings (e.g. requirement of probability density functions (PDF) of random variables, inevitable iterative computation, requirement of design points) of other methods. However, in the existing third-moment method, the iterative computation is required. In this paper, the application of the existing third-moment method is inspected and a simpler method is proposed. In the computation of the target mean resistance, one-time iteration in the existing third-moment method is further simplified to no iteration, by changing the equation of the target reliability to another one. In addition, there is not any mathematical limitation in the new equation of the target reliability. From the proposed method in this paper, it can be concluded that: 1) the present method gives good improvement upon the method based on the third-moment method

2) the computation of the existing third-moment method is further simplified to no iteration

3) the limitations of applicable range in exiting third-moment methods are avoided

4) the accuracy of the proposed method is proved to be higher than the exiting third-moment methods. With several examples, the comparison of the existing third-moment method, the ASCE method and the proposed method is given .The results show that the proposed method is accurate, simple and safe.