عنوان مقاله [English]
For many years, providing sufficient strength for buildings, whilst trying to prevent collapse, was the most important purpose behind seismic codes. Afterthe Northridge earthquake (1994) and the amount of damage due to brittle behavior in steel structure connections, many studies about degrading effects have been undertaken. One of the most important degrading behaviors was in-cycle strength degradation. In recent years, many researchers have focused on in-cycle strength degradation in hysteresis cycles. In this phenomenon,
degradation occurs in the same cycle of loading. Recent investigations done by FEMA-P440A, have shown that the effects of in-cycle strength degradation can be critical in determining the possibility of lateral dynamic instability in Single Degree Of Freedom (SDOF) systems. Multi degree of freedom (MDOF) systems have more complicated behavior than SDOF systems. In this research, in order to study the effects of such kinds of degradation, 3, 5 and 7 story steel moment frame buildings with three types of connection (Pre-Northridge,
Post-Northridge and Elastic-Perfectly-Plastic), have been modeled. In order to have a more precise study, a probabilistic seismic design approach has been used and, then, the reliability of structures at pre-defined confidence levels have been calculated, By performing Incremental Dynamic Analysis (IDA), the required parameters in the probabilistic approach, such as demand and capacity, have been calculated. Results of this study have shown that in-cycle strength degradation can greatly increase the likelihood of global dynamic instability and decrease the reliability of mid-rise steel moment frame structures.