A Moment–rotation curve for CFT square columns and steel beams according to reliability analysis

The structural systems are required structural stability under vertical and lateral loads such as wind and earthquake loads. Using the concrete filled square steel tubular (CFT) columns are one of the solutions to make more efficient structures and increase strength and deformation capacity of columns. It is very difficult to understand exact behavior and its characteristics of connections between CFT columns and steel beams because the connections are made different materials and have some rotational rigidities. According to rotational rigidities, it can be classified as semi-rigid or partially restrained connections. The conventional design approaches are using the safety factor based on past experience or using load amplification factors and resistance reduction factors. Safety of structure could not be appraised by the traditional design codes because there are the errors in estimation of loads, material characteristics, the dimensions of members and structural analysis. Therefore, new approach based on the probability concept has been applied to the assessment of structural safety using the reliability concept. In this paper, the reliability index β and the probability of failure P f are attained by Advanced First-Order Second Moment (AFOSM) method. Moment–rotation–reliability index (M– θ–β ) Curves are developed to present the relationship between level of safety and Moment–rotation curves for connections. The developed method can be used to estimate amount of reinforcement to satisfy the target reliability index β T of the structures.