Application of the Endurance Time Method in the Seismic Assessment of Moment-Resisting Reinforced Concrete Frames with Setbacks

Nowadays, many buildings around the world exhibit height irregularities. Given that higher vibration modes can significantly influence the responses of irregular frames, it is essential to investigate the seismic behavior of these structures. In this research, making use of nonlinear dynamic analysis, the seismic behavior of irregular moment resisting frames is assessed. Nonlinear dynamic analysis, due to considering the dynamic characteristics and nonlinear behavior of the structure, is one of the most accurate methods for seismic evaluation of structures. Despite its advantages, the complexity, high computational demands, and time-consuming nature of nonlinear dynamic analysis have led to limited attention from engineers in the design process of conventional structures. In recent years, several efforts have been made to enhance this method, including the development of the Endurance Time method. In this method, acceleration functions are generated using optimization algorithms, reducing the need for excessive use of accelerograms. For this purpose, 3- and 9-story frames with different types of height irregularities are considered. These frames are analyzed using accelerations derived from the Endurance Time method. A comparison of the results indicates that setbacks in building frames significantly influence the dynamic responses. Notably, the difference in drift values between the story where the setback occurs and the others is relatively large. This highlights the need for special attention to the irregularities during the design process of such frames.