Evaluation of low-rise steel moment-resisting frame reliability index based on performance levels

In designing a structure, due to the uncertainty in some parameters, it is necessary to ensure that the design is responsive to the design requirements. For this purpose, the theory of reliability is used. In this study, the reliability of the low-rise steel moment-resisting frame was evaluated based on performance levels. For this purpose, based on the Monte Carlo simulation method, a step-by-step process was presented to use it to calculate the steel moment-resisting frame reliability index for probabilistic constraints of plastic hinges limitation and inter-story drift ratio limitation at each performance level. Also, cross-sectional area, moment of inertia and plastic section modulus of members, modulus of elasticity and yield stress of steel, and gravity loading are considered as random parameters in this study. Finally, using the presented process method, the reliability of a three-story steel moment-resisting frame, which is optimized based on the performance-based design method, was evaluated. The results show that in some plastic hinges at the performance level of immediate occupancy, the probability of plastic rotation less than the acceptance criteria of this level is not desirable, while in other plastic hinges and performance levels, a suitable reliability index was obtained for the probabilistic constraint of plastic rotation constraint. Also, based on the results, it is very unlikely that the inter-story drift ratio of stories will exceed the limits considered at each level of performance.