Assessing Fragility and Gradual Collapse of Eccentrically Braced Steel Frame Using Incremental Dynamic Analysis

Today, extensively eccentrically braced structures are used to absorb seismic energy using link beam elements on beams. The function of this system is defined as yielding this beam elements during an earthquake and remaining safety and elastic of other structure elements. The length of the link beam is expressed as an effective parameter determining the type of behavior of it as shear or flexure, which determines the seismic performance and the amount of seismic energy absorbed by this element in this type of braced frames. In this research, using incremental dynamic analysis on steel frames under far field records and by performing modeling steps in Python version 3.8 and using of OpenSeesPy documentation, the variables of failure and frame reliability have been investigated. In this research, two samples of 6 and 12-story frames with changes the link beam length from 0.4, 0.6 and 0.8 m have been studied. The results show that the behavior of link beams is affected by the characteristics of the earthquake record and the capacity of the link beams with the same length is various for each record. The results of incremental dynamic analysis on the mentioned frames with different link lengths have shown that the length of short shear link beam in medium height frames has resulted in better seismic behavior and the optimal length of the link beam should be selected after seismic evaluation under different records. The maximum acceleration of the median collapse in this research has been obtained for 6-story frames and the link with 0.6 m length is 5.10, and for 12-story frame with the link of 0.6 m length, 4.20 times the acceleration of the earth's gravity.