Narrow Results

In this paper, an optimization method is used to determine the values of partial factors in structural reliability analysis. Once the proper objective function is defined, a group of optimum partial factors, which enable the objective function to take its minimum value, will need to be determined. In the present study, two kinds of objective function are considered. The conditions that have to be satisfied for optimum partial factors of these two kinds of objective function are then derived. In both cases, the result shows that the partial factors of both dead and live loads should satisfy the same proportional expression and should be inversely proportional to the partial factor of resistance force. A simple beam is used as an example to illustrate the computations involved. It is found that the design concept proposed in this paper leads to a design criterion similar to that which applies to the conventional deterministic method. Thus, this concept can be easily used in practice. The illustrative example shows that the values of the dead load and live load have a significant effect on the reliability design criteria.

The arch dam design specification (SL282-2003) provides an allowable safety factor of 3.5 in abutment stability analysis, whether at the same level with value of 3.0 specified for gravity dams, or greater than it, which is preferred. Using the approach of ‘Ratio of Safety Margin’ proposed by the authors, this method can compare the safety factor with reliability index. Through computing the ratio safety margin can compare safety factor and reliability index whether at the same risk level, the researches confirm that allowable reliability index of 4.45 and the allowable safety factor of 3.5 at the same level of risk control.