Abstract
The structural importance factor is essential in the reliability-based design of structural systems, affecting both dependent and independent failure modes. This factor is crucial for ensuring that the design meets the necessary safety and performance standards by considering uncertainties in material properties, load effects, and other relevant conditions. It adjusts the design parameters to achieve a target reliability level, which is vital for both individual components and the entire system. In this study, a reliability analysis of a frame system unit, represented by its main components, was conducted to determine the effect of the importance factor for each element on the overall survivor function of the frame, considering both dependent and independent failure.
Fault trees and reliability block diagrams represented the structure function, and the importance factor was determined using Birnbaum’s concept, which was employed for evaluating the structure-function for the two cases. For independent failure, a comparison of the main objective function of the steel frame optimally designed units was performed with and without the importance factor effect, while for dependent failure, the β factor method was used to show the difference in the survivor function of the whole steel frame unit with and without using the importance factors of each component. The designed results show that including the importance factor in the analysis played a significant role in the resulting bolts diameter (10%) and shows a lesser effect in the case of beam and column, given that the type and degree of failure severity of the whole system as a unit are more closely linked to the design of these elements than other structural members. The use of the importance factor in this study revealed the significance of each structural member and the most important considerations taken into account when designing it, such as the strength reduction factor and the impact of its failure type on the failure of the entire system.