Reliability analysis for load factors in steel bulk material handling structures with respect to AS4324.1

AS 4324.1 Mobile equipment for continuous handling of bulk materials Part 1: General requirements for the design of steel structures allows the adoption of both permissible stress design (PSD) and limit state design (LSD) philosophies for the design of structural steel members. To assess the cost-safety balance of the load and capacity factors provided in AS 4324.1 for steel column sections subjected to concentrated axial compression and bi-axial bending, this study estimates the reliability of steel columns based on AS 4324.1, considering both PSD and LSD methods based on a statistical rationale. In addition, this study estimates the reliability of steel columns when using the newly proposed load factors for LSD design to ensure that they improve the performance of the current code in terms of the optimal cost-safety balance. This study incorporates the Monte Carlo simulations to consider the uncertainties in design parameters, loads and resistance and load prediction models. As representative examples, five load combinations (I, II/1, III/6, III/8 and III/10) for two design scenarios are considered for an 1850t reclaimer and a 400t stacker. For load combinations I and II/1, the reliability indices that are achieved by the current safety margins of AS 4324.1 for LSD and PSD methods are relatively high compared with the target reliability index, β = 3.8. For load combinations III/6, III/8 and III/10, reliability indices are close to the target reliability if the existing capacity factors and the factors of safety are used. The proposed capacity factors enable one to achieve a consistent safety level for all load combinations. Based on these results, it is recommended to update the current safety margins with the proposed values to ensure consistent safety levels especially, for load cases III/6, III/8 and III/10.